KSH man page

Conditional expressions
ksh(1)                                                                  ksh(1)



NAME
     ksh, rksh - KornShell, a standard/restricted command and programming
     language

SYNOPSIS
     ksh  [ -abCefhikmnprstuvx ] [ -o option ] ... [ -
-c      string ]
          [ arg . . . ]
     rksh [ -abCefhikmnprstuvx ] [ -o option ] ... 
 -c     string ]
          [ arg . . . ]

DESCRIPTION
     ksh is a command and programming language that executes commands read
     from a terminal or a file.  rksh is a restricted version of the command
     interpreter ksh; it is used to set up login names and execution
     environments whose capabilities are more controlled than those of the
     standard shell.  See Invocation below for the meaning of arguments to the
     shell.

   Definitions.
     A metacharacter is one of the following characters:

          ;   &   (   )   |   <   >   new-line   space   tab

     A blank is a tab or a space.  An identifier is a sequence of letters,
     digits, or underscores starting with a letter or underscore.  Identifiers
     are used as names for functions and variables.  A word is a sequence of
     characters separated by one or more non-quoted metacharacters.

     A command is a sequence of characters in the syntax of the shell
     language.  The shell reads each command and carries out the desired
     action either directly or by invoking separate utilities.  A special
     command is a command that is carried out by the shell without creating a
     separate process.  Except for documented side effects, most special
     commands can be implemented as separate utilities.

   Commands.
     A simple-command is a sequence of blank separated words which may be
     preceded by a variable assignment list (see Environment below).  The
     first word specifies the name of the command to be executed.  Except as
     specified below, the remaining words are passed as arguments to the
     invoked command.  The command name is passed as argument 0 [see exec(2)].
     The value of a simple-command is its exit status if it terminates
     normally, or (octal) 200+status if it terminates abnormally [see
     signal(2) for a list of status values].

     A pipeline is a sequence of one or more commands separated by |.  The
     standard output of each command but the last is connected by a pipe(2) to
     the standard input of the next command.  Each command is run as a
     separate process; the shell waits for the last command to terminate.  The
     exit status of a pipeline is the exit status of the last command.

     A list is a sequence of one or more pipelines separated by ;, &, &&, or
     ||, and optionally terminated by ;, &, or |&.  Of these five symbols, ;,
     &, and |& have equal precedence, which is lower than that of && and ||.
     The symbols && and || also have equal precedence.  A semicolon (;) causes
     sequential execution of the preceding pipeline; an ampersand (&) causes
     asynchronous execution of the preceding pipeline (that is, the shell does
     not wait for that pipeline to finish).  The symbol |& causes asynchronous
     execution of the preceding command or pipeline with a two-way pipe
     established to the parent shell.  The standard input and output of the
     spawned command can be written to and read from by the parent shell using
     the -p option of the special commands read and print described later.
     The symbol && (||) causes the list following it to be executed only if
     the preceding pipeline returns a zero (non-zero) value.  An arbitrary
     number of new-lines may appear in a list, instead of a semicolon, to
     delimit a command.

     A command is either a simple-command or one of the following.  Unless
     otherwise stated, the value returned by a command is that of the last
     simple-command executed in the command.

     for identifier [ in word ... ] ;do list ;done
          Each time a for command is executed, identifier is set to the next
          word taken from the in word list.  If in word ...  is omitted, then
          the for command executes the do list once for each positional
          parameter that is set (see Parameter Substitution below).  Execution
          ends when there are no more words in the list.

     select identifier [ in word ... ] ;do list ;done
          A select command prints on standard error (file descriptor 2), the
          set of words, each preceded by a number.  If in word ...  is
          omitted, then the positional parameters are used instead (see
          Parameter Substitution below).  The PS3 prompt is printed and a line
          is read from the standard input.  If this line consists of the
          number of one of the listed words, then the value of the parameter
          identifier is set to the word corresponding to this number.  If this
          line is empty the selection list is printed again.  Otherwise the
          value of the parameter identifier is set to null.  The contents of
          the line read from standard input is saved in the variable REPLY.
          The list is executed for each selection until a break or end-of-file
          is encountered.

     case word in [ [(]pattern [ | pattern ] ... ) list ;; ] ... esac
          A case command executes the list associated with the first pattern
          that matches word.  The form of the patterns is the same as that
          used for file-name generation (see File Name Generation below).

     if list ;then list [ elif list ;then list ] ... [ ;else
e list ] ;fi
          The list following if is executed and, if it returns a zero exit
          status, the list following the first then is executed.  Otherwise, the
          list following elif is executed and, if its value is zero, the list
          following the next then is executed.  Failing that, the else list is
          executed.  If no else list or then list is executed, then the if
          command returns a zero exit status.

     while list ;do list ;done
          A while command repeatedly executes the while list and, if the exit
          status of the last command in the list is zero, executes the do
          list; otherwise the loop terminates.  If no commands in the do list
          are executed, then the while command returns a zero exit status;
          until may be used in place of while to negate the loop termination
          test.

     (list)
          Execute list in a separate environment.  Note, that if two adjacent
          open parentheses are needed for nesting, a space must be inserted to
          avoid arithmetic evaluation as described below.

     { list;}
          list is simply executed.  The { must be followed by a space.  Note
          that unlike the metacharacters ( and ), { and } are reserved words
          and must be typed at the beginning of a line or after a ; in order
          to be recognized.

     [[expression]]
          Evaluates expression and returns a zero exit status when expression
          is true.  See Conditional Expressions below, for a description of
          expression.

     function identifier { list ;}
     identifier () { list ;}
          Define a function which is referenced by identifier.  The body of
          the function is the list of commands between { and }.  (see
          Functions below).  The { must be followed by a space.

     time pipeline
          The pipeline is executed and the elapsed time as well as the user
          and system time are printed on standard error.  Note that the
          reported times reflect the elapsed time for both the parent and the
          child processes in order to give a more accurate view of the total
          time the pipeline took to execute.

     The following reserved words are only recognized as the first word of a
     command and when not quoted:

     if then else elif fi case esac for
while until do done { } function
     select time [[ ]]

   Comments.
     A word beginning with # causes that word and all the following characters
     up to a new-line to be ignored.

   Aliasing.
     The first word of each command is replaced by the text of an alias if an
     alias for this word has been defined.  An alias name consists of any
     number of characters excluding meta-characters, quoting characters, file
     expansion characters, parameter and command substitution characters and
     =.  The replacement string can contain any valid shell script including
     the metacharacters listed above.  The first word of each command in the
     replaced text, other than any that are in the process of being replaced,
     will be tested for aliases.  If the last character of the alias value is
     a blank then the word following the alias will also be checked for alias
     substitution.  Aliases can be used to redefine special builtin commands
     but cannot be used to redefine the reserved words listed above.  Aliases
     can be created, listed, and exported with the alias command and can be
     removed with the unalias command.  Exported aliases remain in effect for
     scripts invoked by name, but must be reinitialized for separate
     invocations of the shell (see Invocation below).

     Aliasing is performed when scripts are read, not while they are executed.
     Therefore, for an alias to take effect the alias definition command has
     to be executed before the command which references the alias is read.

     Aliases are frequently used as a short hand for full path names.  An
     option to the aliasing facility allows the value of the alias to be
     automatically set to the full pathname of the corresponding command.
     These aliases are called tracked aliases.  The value of a tracked alias
     is defined the first time the corresponding command is looked up and
     becomes undefined each time the PATH variable is reset.  These aliases
     remain tracked so that the next subsequent reference will redefine the
     value.  Several tracked aliases are compiled into the shell.  The -h
     option of the set command makes each referenced command name into a
     tracked alias.

     The following exported aliases are compiled into the shell but can be
     unset or redefined:

          autoload='typeset -fu'
          false='let 0'
          functions='typeset -f'
          hash='alias -t'
          history='fc -l'
          integer='typeset -i'
          nohup='nohup '
          r='fc -e -'
          true=':'
          type='whence -v'

   Tilde Substitution.
     After alias substitution is performed, each word is checked to see if it
     begins with an unquoted _.  If it does, then the word up to a / is
     checked to see if it matches a user name in the /etc/passwd file.  If a
     match is found, the _ and the matched login name is replaced by the login
     directory of the matched user.  This is called a tilde substitution.  If
     no match is found, the original text is left unchanged.  A _ by itself,
     or in front of a /, is replaced by $HOME.  A _ followed by a + or - is
     replaced by $PWD and $OLDPWD respectively.   ~

     In addition, tilde substitution is attempted when the value of a variable
     assignment begins with a _.
                              ~
   Command Substitution.
     The standard output from a command enclosed in parentheses preceded by a
     dollar sign ( $() ) or a pair of grave accents (``) may be used as part
     or all of a word; trailing new-lines are removed.  In the second
     (archaic) form, the string between the quotes is processed for special
     quoting characters before the command is executed (see Quoting below).
     The command substitution $(cat file) can be replaced by the equivalent
     but faster $( ''.
          PS3  Selection prompt string used within a select loop, by default
               ``#? ''.
          PS4  The value of this variable is expanded for parameter
               substitution and precedes each line of an execution trace.  If
               omitted, the execution trace prompt is ``+ ''.
          SHELL
               The pathname of the shell is kept in the environment.  At
               invocation, if the basename of this variable matches the
               pattern *r*sh, then the shell becomes restricted.
          TMOUT
               If set to a value greater than zero, the shell will terminate
               if a command is not entered within the prescribed number of
               seconds after issuing the PS1 prompt.  (Note that the shell can
               be compiled with a maximum bound for this value which cannot be
               exceeded.)
          VISUAL
               If the value of this variable ends in vi then the corresponding
               option (see Special Command set below) will be turned on.
     The shell gives default values to PATH, PS1, PS2, MAILCHECK, TMOU_
T       and
     IFS.  HOME, MAIL and SHELL are set by login(1).

   Blank Interpretation.
     After parameter and command substitution, the results of substitutions
     are scanned for the field separator characters ( those found in IFS ) and
     split into distinct arguments where such characters are found.  Explicit
     null arguments ("" or '') are retained.  Implicit null arguments (those
     resulting from parameters that have no values) are removed.

   File Name Generation.
     Following substitution, each command word is scanned for the characters
     *, ?, and [ unless the -f option has been set.  If one of these
     characters appears then the word is regarded as a pattern.  The word is
     replaced with lexicographically sorted file names that match the pattern.
     If no file name is found that matches the pattern, then the word is left
     unchanged.  When a pattern is used for file name generation, the
     character .  at the start of a file name or immediately following a /, as
     well as the character / itself, must be matched explicitly.  In other
     instances of pattern matching the / and .  are not treated specially.

          *    Matches any string, including the null string.
          ?    Matches any single character.
          [...]
               Matches any one of the enclosed characters.  A pair of
               characters separated by - matches any character lexically
               between the pair, inclusive.  If the first character following
               the opening "[ " is a "!" then any character not enclosed is
               matched.  A - can be included in the character set by putting
               it as the first or last character.

     A pattern-list is a list of one or more patterns separated from each
     other with a |.  Composite patterns can be formed with one or more of the
     following:

          ?(pattern-list)
               Optionally matches any one of the given patterns.
          *(pattern-list)
               Matches zero or more occurrences of the given patterns.
          +(pattern-list)
               Matches one or more occurrences of the given patterns.
          @(pattern-list)
               Matches exactly one of the given patterns.
          !(pattern-list)
               Matches anything, except one of the given patterns.

   Quoting.
     Each of the metacharacters listed above (see Definitions above) has a
     special meaning to the shell and causes termination of a word unless
     quoted.  A character may be quoted (that is, made to stand for itself) by
     preceding it with a \.  The pair \new-line is removed.  All characters
     enclosed between a pair of single quote marks (''), are quoted.  A single
     quote cannot appear within single quotes.  Inside double quote marks
     (""), parameter and command substitution occurs and \ quotes the
     characters \, `, ", and $.  The meaning of $* and $@ is identical when
     not quoted or when used as a variable assignment value or as a file name.
     However, when used as a command argument, "$*" is equivalent to
     "$1d$2d...", where d is the first character of the IFS variable, whereas
     "$@" is equivalent to "$1"d"$2"d...  Inside grave quote marks (``) \
     quotes the characters \, `, and $.  If the grave quotes occur within
     double quotes then \ also quotes the character ".

     The special meaning of reserved words or aliases can be removed by
     quoting any character of the reserved word.  The recognition of function
     names or special command names listed below cannot be altered by quoting
     them.

   Arithmetic Evaluation.
     An ability to perform integer arithmetic is provided with the special
     command let.  Evaluations are performed using long arithmetic.  Constants
     are of the form [base#]n where base is a decimal number between two and
     thirty-six representing the arithmetic base and n is a number in that
     base.  If base# is omitted then base 10 is used.

     An arithmetic expression uses the same syntax, precedence, and
     associativity of expression of the C language.  All the integral
     operators, other than ++, --, ?:, and , are supported.  Variables can be
     referenced by name within an arithmetic expression without using the
     parameter substitution syntax.  When a variable is referenced, its value
     is evaluated as an arithmetic expression.

     An internal integer representation of a variable can be specified with
     the -i option of the typeset special command.  Arithmetic evaluation is
     performed on the value of each assignment to a variable with the -i
     attribute.  If you do not specify an arithmetic base, the first
     assignment to the variable determines the arithmetic base.  This base is
     used when parameter substitution occurs.

     Since many of the arithmetic operators require quoting, an alternative
     form of the let command is provided.  For any command which begins with a
     ((, all the characters until a matching )) are treated as a quoted
     expression.  More precisely, ((...))  is equivalent to let "...".

   Prompting.
     When used interactively, the shell prompts with the parameter expanded
     value of PS1 before reading a command.  If at any time a new-line is
     typed and further input is needed to complete a command, then the
     secondary prompt (that is, the value of PS2) is issued.

   Conditional Expressions.
     A conditional expression is used with the [[ compound command to test
     attributes of files and to compare strings.  Word splitting and file name
     generation are not performed on the words between [[ and ]].  Each
     expression can be constructed from one or more of the following unary or
     binary expressions:
     -a file   True, if file exists.
     -b file   True, if file exists and is a block special file.
     -c file   True, if file exists and is a character special file.
     -d file   True, if file exists and is a directory.
     -e file   Same as -a file.
     -f file   True, if file exists and is an ordinary file.
     -g file   True, if file exists and is has its setgid bit set.
     -k file   True, if file exists and is has its sticky bit set.
     -n string True, if length of string is non-zero.
     -o option True, if option named option is on.
     -p file   True, if file exists and is a fifo special file or a pipe.
     -r file   True, if file exists and is readable by current process.
     -s file   True, if file exists and has size greater than zero.
     -t fildes True, if file descriptor number fildes is open and associated
               with a terminal device.
     -u file   True, if file exists and is has its setuid bit set.
     -w file   True, if file exists and is writable by current process.
     -x file   True, if file exists and is executable by current process.  If
               file exists and is a directory, then the current process has
               permission to search in the directory.
     -z string True, if length of string is zero.
     -L file   True, if file exists and is a symbolic link.
     -O file   True, if file exists and is owned by the effective user id of
               this process.
     -G file   True, if file exists and its group matches the effective group
               id of this process.
     -S file   True, if file exists and is a socket.
     file1 -nt file2
               True, if file1 exists and is newer than file2.
     file1 -ot file2
               True, if file1 exists and is older than file2.
     file1 -ef file2
               True, if file1 and file2 exist and refer to the same file.
     string = pattern
               True, if string matches pattern.
     string != pattern
               True, if string does not match pattern.
     string1 < string2
               True, if string1 comes before string2 based on ASCII value of
               their characters.
     string1 > string2
               True, if string1 comes after string2 based on ASCII value of
               their characters.
     exp1 -eq exp2
               True, if exp1 is equal to exp2.
     exp1 -ne exp2
               True, if exp1 is not equal to exp2.
     exp1 -lt exp2
               True, if exp1 is less than exp2.
     exp1 -gt exp2
               True, if exp1 is greater than exp2.
     exp1 -le exp2
               True, if exp1 is less than or equal to exp2.
     exp1 -ge exp2
               True, if exp1 is greater than or equal to exp2.

     In each of the above expressions, if file is of the form /dev/fd/n, where
     n is an integer, then the test applied to the open file whose descriptor
     number is n.

     A compound expression can be constructed from these primitives by using
     any of the following, listed in decreasing order of precedence.
     (expression)    True, if expression is true.  Used to group expressions.
     ! expression    True if expression is false.
     expression1 && expression2
                     True, if expression1 and expression2 are both true.
     expression1 || expression2
                     True, if either expression1 or expression2 is true.

   Input/Output.
     Before a command is executed, its input and output may be redirected
     using a special notation interpreted by the shell.  The following may
     appear anywhere in a simple-command or may precede or follow a command
     and are not passed on to the invoked command.  Command and parameter
     substitution occurs before word
     or digit is used except as noted below.  File name generation occurs only
     if the pattern matches a single file and blank interpretation is not
     performed.

     word         Use file word as standard output (file descriptor 1).  If
                   the file does not exist then it is created.  If the file
                   exists, is a regular file, and the noclobber option is on,
                   this causes an error; otherwise, it is truncated to zero
                   length.

     >|word        Sames as >, except that it overrides the noclobber option.

     >>word        Use file word as standard output.  If the file exists then
                   output is appended to it (by first seeking to the end-of-
                   file); otherwise, the file is created.

     <>word        Open file word for reading and writing as standard input.

     <<[-]word     The shell input is read up to a line that is the same as
                   word, or to an end-of-file.  No parameter substitution,
                   command substitution or file name generation is performed
                   on word.  The resulting document, called a here-document,
                   becomes the standard input.  If any character of word is
                   quoted, then no interpretation is placed upon the
                   characters of the document; otherwise, parameter and
                   command substitution occurs, \new-line is ignored, and \
                   must be used to quote the characters \, $, `, and the first
                   character of word.  If - is appended to <<, then all
                   leading tabs are stripped from word and from the document.

     <&digit       The standard input is duplicated from file descriptor digit
                   [see dup(2)].  Similarly for the standard output using >&
                   digit.

     <&-           The standard input is closed.  Similarly for the standard
                   output using >&-.

     <&p           The input from the co-process is moved to standard input.

     >&p           The output to the co-process is moved to standard output.

     If one of the above is preceded by a digit, then the file descriptor
     number referred to is that specified by the digit (instead of the default
     0 or 1).  For example:

          ... 2>&1

     means file descriptor 2 is to be opened for writing as a duplicate of
     file descriptor 1.

     The order in which redirections are specified is significant.  The shell
     evaluates each redirection in terms of the (file descriptor, file)
     association at the time of evaluation.  For example:

          ... 1>fname 2>&1

     first associates file descriptor 1 with file fname.  It then associates
     file descriptor 2 with the file associated with file descriptor 1 (that
     is, fname).  If the order of redirections were reversed, file descriptor
     2 would be associated with the terminal (assuming file descriptor 1 had
     been) and then file descriptor 1 would be associated with file fname.

     If a command is followed by & and job control is not active, then the
     default standard input for the command is the empty file /dev/null.
     Otherwise, the environment for the execution of a command contains the
     file descriptors of the invoking shell as modified by input/output
     specifications.

   Environment.
     The environment [see environ(5)] is a list of name-value pairs that is
     passed to an executed program in the same way as a normal argument list.
     The names must be identifiers and the values are character strings.  The
     shell interacts with the environment in several ways.  On invocation, the
     shell scans the environment and creates a variable for each name found,
     giving it the corresponding value and marking it export . Executed
     commands inherit the environment.  If the user modifies the values of
     these variables or creates new ones, using the export or typeset -x
     commands they become part of the environment.  The environment seen by
     any executed command is thus composed of any name-value pairs originally
     inherited by the shell, whose values may be modified by the current
     shell, plus any additions which must be noted in export or typeset -x
     commands.

     The environment for any simple-command or function may be augmented by
     prefixing it with one or more variable assignments.  A variable
     assignment argument is a word of the form identifier=value.  Thus:

          TERM=450 cmd args                  and
          (export TERM; TERM=450; cmd args)

     are equivalent (as far as the above execution of cmd is concerned except
     for commands listed with one or two daggers, -, in the Special Commands
     section).

     If the -k flag is set, all variable assignment arguments are placed in
     the environment, even if they occur after the command name.  The
     following first prints a=b c and then c:

          echo a=b c
          set -k
          echo a=b c
     This feature is intended for use with scripts written for early versions
     of the shell and its use in new scripts is strongly discouraged.  It is
     likely to disappear someday.

   Functions.
     The function reserved word, described in the Commands section above, is
     used to define shell functions.  Shell functions are read in and stored
     internally.  Alias names are resolved when the function is read.
     Functions are executed like commands with the arguments passed as
     positional parameters (see Execution below). The special positional
     parameter $0 is the name of invoking program, not the name of the
     function.

     Functions execute in the same process as the caller and share all files
     and present working directory with the caller.  Traps caught by the
     caller are reset to their default action inside the function.  A trap
     condition that is not caught or ignored by the function causes the
     function to terminate and the condition to be passed on to the caller.  A
     trap on EXIT set inside a function is executed after the function
     completes in the environment of the caller.  Ordinarily, variables are
     shared between the calling program and the function.  However, the
     typeset special command used within a function defines local variables
     whose scope includes the current function and all functions it calls.

     The special command return is used to return from function calls.  Errors
     within functions return control to the caller.
     Function identifiers can be listed with the -f or +f option of the
     typeset special command.  The text of functions may also be listed with
     -f.  Function can be undefined with the -f option of the unset special
     command.

     Ordinarily, functions are unset when the shell executes a shell script.
     The -xf option of the typeset command allows a function to be exported to
     scripts that are executed without a separate invocation of the shell.
     Functions that need to be defined across separate invocations of the
     shell should be specified in the ENV file with the -xf option of typeset.

   Jobs.
     If the monitor option of the set command is turned on, an interactive
     shell associates a job with each pipeline.  It keeps a table of current
     jobs, printed by the jobs command, and assigns them small integer
     numbers.  When a job is started asynchronously with &, the shell prints a
     line which looks like:

          [1] 1234

     indicating that the job which was started asynchronously was job number 1
     and had one (top-level) process, whose process id was 1234.

     If you are running a job and wish to do something else you may hit the
     key ^Z (CTRL-z) which sends a STOP signal to the current job.  The shell
     will then normally indicate that the job has been `Stopped', and print
     another prompt.  You can then manipulate the state of this job, putting
     it in the background with the bg command, or run some other commands and
     then eventually bring the job back into the foreground with the
     foreground command fg.  A ^Z takes effect immediately and is like an
     interrupt in that pending output and unread input are discarded when it
     is typed.

     A job being run in the background will stop if it tries to read from the
     terminal.  Background jobs are normally allowed to produce output, but
     this can be disabled by giving the command ``stty tostop''.  If you set
     this tty option, then background jobs will stop when they try to produce
     output like they do when they try to read input.

     There are several ways to refer to jobs in the shell.  A job can be
     referred to by the process id of any process of the job or by one of the
     following:
        %number
               The job with the given number.
        %string
               Any job whose command line begins with string.
        %?string
               Any job whose command line contains string.
        %%     Current job.
        %+     Equivalent to %%.
     This shell learns immediately whenever a process changes state.  It
     normally informs you whenever a job becomes blocked so that no further
     progress is possible, but only just before it prints a prompt.  This is
     done so that it does not otherwise disturb your work.

     When the monitor mode is on, each background job that completes triggers
     any trap set for CHLD.

     When you try to leave the shell while jobs are running or stopped, you
     will be warned that `You have stopped(running) jobs.'  You may use the
     jobs command to see what they are.  If you do this or immediately try to
     exit again, the shell will not warn you a second time, and the stopped
     jobs will be terminated.

   Signals.
     When a command is run in the background (that it, when it is followed by
     &) and the job monitor option is active, the command does not receive
     INTERRUPT or QUIT signals.  When a command is run in the background (that
     it, when it is followed by &) and the job monitor option is not active,
     the command receives INTERRUPT or QUIT signals but ignores them.
     Otherwise, signals have the values inherited by the shell from its parent
     (but see also the trap command below).

   Execution.
     Each time a command is executed, the above substitutions are carried out.
     If the command name matches one of the Special Commands listed below, it
     is executed within the current shell process.  Next, the command name is
     checked to see if it matches one of the user defined functions.  If it
     does, the positional parameters are saved and then reset to the arguments
     of the function call.  When the function completes or issues a return,
     the positional parameter list is restored and any trap set on EXIT within
     the function is executed.  The value of a function is the value of the
     last command executed.  A function is also executed in the current shell
     process.  If a command name is not a special command or a user defined
     function, a process is created and an attempt is made to execute the
     command via exec(2).

     The shell variable PATH defines the search path for the directory
     containing the command.  Alternative directory names are separated by a
     colon (:).  The default path is /usr/bin:  (specifying /usr/bin and the
     current directory in that order).  The current directory can be specified
     by two or more adjacent colons, or by a colon at the beginning or end of
     the path list.  If the command name contains a / then the search path is
     not used.  Otherwise, each directory in the path is searched for an
     executable file.  If the file has execute permission but is not a
     directory or an a.out file, it is assumed to be a file containing shell
     commands.  A sub-shell is spawned to read it.  All non-exported aliases,
     functions, and variables, are removed in this case.  A parenthesized
     command is executed in a sub-shell without removing non-exported
     quantities.

   Command Re-entry.
     The text of the last HISTSIZE (default 128) commands entered from a
     terminal device is saved in a history file.  The file $HOME/.sh_history
     is used if the file denoted by the HISTFILE variable is not set or is not
     writable.  A shell can access the commands of all interactive shells
     which use the same named HISTFILE.  The special command fc is used to
     list or edit a portion of this file.  The portion of the file to be
     edited or listed can be selected by number or by giving the first
     character or characters of the command.  A single command or range of
     commands can be specified.  If you do not specify an editor program as an
     argument to fc then the value of the variable FCEDIT is used.  If FCEDIT
     is not defined then /usr/bin/ed is used.  The edited command(s) is
     printed and re-executed upon leaving the editor.  The editor name - is
     used to skip the editing phase and to re-execute the command.  In this
     case a substitution variable of the form old=new can be used to modify
     the command before execution.  For example, if r is aliased to 'fc -e -'
     then typing `r bad=good c' will re-execute the most recent command which
     starts with the letter c, replacing the first occurrence of the string
     bad with the string good.

   In-line Editing Options
     Normally, each command line entered from a terminal device is simply
     typed followed by a new-line (`RETURN' or `LINE FEED').  If the vi option
     is active, the user can edit the command line.  To be in this edit mode
     set the vi option.  An editing option is automatically selected each time
     the VISUAL or EDITOR variable is assigned a value ending in either of
     these option names.

     The editing features require that the user's terminal accept `RETURN' as
     carriage return without line feed and that a space (` ') must overwrite
     the current character on the screen.

     The editing mode implements a concept where the user is looking through a
     window at the current line.  The window width is the value of COLUMNS if
     it is defined, otherwise 80.  If the line is longer than the window width
     minus two, a mark is displayed at the end of the window to notify the
     user.  As the cursor moves and reaches the window boundaries the window
     will be centered about the cursor.  The mark is a > (<, *) if the line
     extends on the right (left, both) side(s) of the window.

     The search commands in each edit mode provide access to the history file.
     Only strings are matched, not patterns, although a leading ^ in the
     string restricts the match to begin at the first character in the line.

   vi Editing Mode
     There are two typing modes.  Initially, when you enter a command you are
     in the input mode.  To edit, the user enters control mode by typing ESC
     (\033) and moves the cursor to the point needing correction and then
     inserts or deletes characters or words as needed.  Most control commands
     accept an optional repeat count prior to the command.

     When in vi mode on most systems, canonical processing is initially
     enabled and the command will be echoed again if the speed is 1200 baud or
     greater and it contains any control characters or less than one second
     has elapsed since the prompt was printed.  The ESC character terminates
     canonical processing for the remainder of the command and the user can
     then modify the command line.  This scheme has the advantages of
     canonical processing with the type-ahead echoing of raw mode.

     If the option viraw is also set, the terminal will always have canonical
     processing disabled.

        Input Edit Commands
          By default the editor is in input mode.
          erase     (User defined erase character as defined by the stty
                    command, usually ^H or #.)  Delete previous character.
          ^W        Delete the previous blank separated word.
          ^D        Terminate the shell.
          ^V        Escape next character.  Editing characters, the user's
                    erase or kill characters may be entered in a command line
                    or in a search
                    string if preceded by a ^V.  The ^V removes the next
                    character's editing features (if any).
          \         Escape the next erase or kill character.
        Motion Edit Commands
          These commands will move the cursor.
          [count]l  Cursor forward (right) one character.
          [count]w  Cursor forward one alpha-numeric word.
          [count]W  Cursor to the beginning of the next word that follows a
                    blank.
          [count]e  Cursor to end of word.
          [count]E  Cursor to end of the current blank delimited word.
          [count]h  Cursor backward (left) one character.
          [count]b  Cursor backward one word.
          [count]B  Cursor to preceding blank separated word.
          [count]|  Cursor to column count.
          [count]fc Find the next character c in the current line.
          [count]Fc Find the previous character c in the current line.
          [count]tc Equivalent to f followed by h.
          [count]Tc Equivalent to F followed by l.
          [count];  Repeats count times, the last single character find
                    command, f, F, t, or T.
          [count],  Reverses the last single character find command count
                    times.
          0         Cursor to start of line.
          ^         Cursor to first non-blank character in line.
          $         Cursor to end of line.
        Search Edit Commands
          These commands access your command history.
          [count]k  Fetch previous command.  Each time k is entered the
                    previous command back in time is accessed.
          [count]-  Equivalent to k.
          [count]j  Fetch next command.  Each time j is entered the next
                    command forward in time is accessed.
          [count]+  Equivalent to j.
          [count]G  The command number count is fetched.  The default is the
                    least recent history command.
          /string   Search backward through history for a previous command
                    containing string.  String is terminated by a "RETURN" or
                    "NEW LINE".  If string is preceded by a ^, the matched
                    line must begin with string.  If string is null the
                    previous string will be used.
          ?string   Same as / except that search will be in the forward
                    direction.
          n         Search for next match of the last pattern to / or ?
                    commands.
          N         Search for next match of the last pattern to / or ?, but
                    in reverse direction.  Search history for the string
                    entered by the previous / command.
        Text Modification Edit Commands
          These commands will modify the line.
          a         Enter input mode and enter text after the current
                    character.
          A         Append text to the end of the line.  Equivalent to $a.
          [count]cmotion
          c[count]motion
                    Delete current character through the character that motion
                    would move the cursor to and enter input mode.  If motion
                    is c, the entire line will be deleted and input mode
                    entered.
          C         Delete the current character through the end of line and
                    enter input mode.  Equivalent to c$.
          S         Equivalent to cc.
          D         Delete the current character through the end of line.
                    Equivalent to d$.
          [count]dmotion
          d[count]motion
                    Delete current character through the character that motion
                    would move to.  If motion is d, the entire line will be
                    deleted.
          i         Enter input mode and insert text before the current
                    character.
          I         Insert text before the beginning of the line.  Equivalent
                    to 0i.
          [count]P  Place the previous text modification before the cursor.
          [count]p  Place the previous text modification after the cursor.
          R         Enter input mode and replace characters on the screen with
                    characters you type overlay fashion.
          [count]rc Replace the count character(s) starting at the current
                    cursor position with c, and advance the cursor.
          [count]x  Delete current character.
          [count]X  Delete preceding character.
          [count].  Repeat the previous text modification command.
          [count]_  Invert the case of the count character(s) starting at the
                 ~  current cursor position and advance the cursor.
          [count]_  Causes the count word of the previous command to be
                    appended and input mode entered.  The last word is used if
                    count is omitted.
          *         Causes an * to be appended to the current word and file
                    name generation attempted.  If no match is found, it rings
                    the bell.  Otherwise, the word is replaced by the matching
                    pattern and input mode is entered.
          \         Filename completion.  Replaces the current word with the
                    longest common prefix of all filenames matching the
                    current word with an asterisk appended.  If the match is
                    unique, a / is appended if the file is a directory and a
                    space is appended if the file is not a directory.
        Other Edit Commands
          Miscellaneous commands.
          [count]ymotion
          y[count]motion
                    Yank current character through character that motion would
                    move the cursor to and puts them into the delete buffer.
                    The text and cursor are unchanged.
          Y         Yanks from current position to end of line.  Equivalent to
                    y$.
          u         Undo the last text modifying command.
          U         Undo all the text modifying commands performed on the
                    line.
          [count]v  Returns the command fc -e ${VISUAL:-${EDITOR
R:-vi}} count
                    in the input buffer.  If count is omitted, then the
                    current line is used.
          ^L        Line feed and print current line.  Has effect only in
                    control mode.
          ^J        (New line) Execute the current line, regardless of mode.
          ^M        (Return) Execute the current line, regardless of mode.
          #         Sends the line after inserting a # in front of the line.
                    Useful for causing the current line to be inserted in the
                    history without being executed.
          =         List the file names that match the current word if an
                    asterisk were appended it.
          @letter   Your alias list is searched for an alias by the name
                    _letter and if an alias of this name is defined, its value
                    will be inserted on the input queue for processing.

   Special Commands.
     The following simple-commands are executed in the shell process.
     The following simple-commands are executed in the shell process.
     Input/Output redirection is permitted.  Unless otherwise indicated, the
     output is written on file descriptor 1 and the exit status, when there is
     no syntax error, is zero.  Commands that are preceded by one or two - are
     treated specially in the following ways:
     1.   Variable assignment lists preceding the command remain in effect
          when the command completes.
     2.   I/O redirections are processed after variable assignments.
     3.   Errors cause a script that contains them to abort.
     4.   Words, following a command preceded by -- that are in the format of
          a variable assignment, are expanded with the same rules as a
          variable assignment.  This means that tilde substitution is
          performed after the = sign and word splitting and file name
          generation are not performed.

     - : [ arg ... ]
          The command only expands parameters.

     - . file [ arg ... ]
          Read the complete file then execute the commands.  The commands are
          executed in the current shell environment.  The search path
          specified by PATH is used to find the directory containing file.  If
          any arguments arg are given, they become the positional parameters.
          Otherwise the positional parameters are unchanged.  The exit status
          is the exit status of the last command executed.

     -- alias [ -tx ]  [ name[ =value  ] ] ...
          Alias with no arguments prints the list of aliases in the form
          name=value on standard output.  An alias is defined for each name
          whose value is given.  A trailing space in value causes the next
          word to be checked for alias substitution.  The -t flag is used to
          set and list tracked aliases.  The value of a tracked alias is the
          full pathname corresponding to the given name.  The value becomes
          undefined when the value of PATH is reset but the aliases remain
          tracked.  Without the -t flag, for each name in the argument list
          for which no value is given, the name and value of the alias is
          printed.  The -x flag is used to set or print exported aliases.  An
          exported alias is defined for scripts invoked by name.  The exit
          status is non-zero if a name is given, but no value, for which no
          alias has been defined.

     bg [ job... ]
          This command is only on systems that support job control.  Puts each
          specified job into the background.  The current job is put in the
          background if job is not specified.  See Jobs for a description of
          the format of job.

     - break [ n ]
          Exit from the enclosing for, while, until or select loop, if any.
          If n is specified then break n levels.

     command [ -p ] command_name [ argument ... ]
     command [ -v | -V ]  command_name

          The command utility causes the shell to treat the arguments as a
          simple command, suppressing the shell function lookup. If the
          command_name is the same as the name of one of the special builtin
          utilities, the special properties in the enumerated list at the
          beginning of "Special Commands" section will not occur. In every
          other respect, if command_name is not the name of a function, the
          effect of command will be the same as omitting command.

          The -p option performs the search using a defualt value for PATH
          that is guaranteed to find all of the standard utilities.

          The -v option will write a string to standard output that indicates
          the pathname or command that will be used by the shell, in the
          current execution environment, to invoke command_name.

          The -V option will write a string to standard output that indicates
          how the name given in the command_name operand will be interpreted
          by the shell in the current shell execution environment. It will
          indicate in which of the following categories command_name falls and
          include the information stated:

          Utilities, regular built-in utilities, and any implementation-
          provided functions that are found using the PATH variable will be
          identified as such and include the absolute pathname in the string.

          Other shell functions will be identified as functions.

          Aliases will be identified as aliases and their definitions will be
          included in the string.

          Special built-in utilities will be identified as special built-in
          utilities.

          Regular built-in utilities not associated with a PATH search will be
          identified as regular built-in utilities.

          Shell reserved words will be identified as reserved words.

     - continue [ n ]
          Resume the next iteration of the enclosing for, while, until or
          select loop.  If n is specified then resume at the n-th enclosing
          loop.

     cd [ arg ]
     cd old new
          This command can be in either of two forms.  In the first form it
          changes the current directory to arg.  If arg is - the directory is
          changed to the previous directory.  The shell variable HOME is the
          default arg.  The variable PWD is set to the current directory.  The
          shell variable CDPATH defines the search path for the directory
          containing arg.  Alternative directory names are separated by a
          colon (:).  The default path is  (specifying the current
          directory).  Note that the current directory is specified by a null
          path name, which can appear immediately after the equal sign or
          between the colon delimiters anywhere else in the path list.  If arg
          begins with a / then the search path is not used.  Otherwise, each
          directory in the path is searched for arg.

          The second form of cd substitutes the string new for the string old
          in the current directory name, PWD and tries to change to this new
          directory.


          The cd command may not be executed by rksh.

     echo [ arg ... ]
          See echo(1) for usage and description.

     - eval [ arg ... ]
          The arguments are read as input to the shell and the resulting
          command(s) executed.

     - exec [ arg ... ]
          If arg is given, the command specified by the arguments is executed
          in place of this shell without creating a new process.  Input/output
          arguments may appear and affect the current process.  If no
          arguments are given the effect of this command is to modify file
          descriptors as prescribed by the input/output redirection list.  In
          this case, any file descriptor numbers greater than 2 that are
          opened with this mechanism are closed when invoking another program.

     - exit [ n ]
          Causes the shell to exit with the exit status specified by n.  If n
          is omitted then the exit status is that of the last command
          executed.  An end-of-file will also cause the shell to exit except
          for a shell which has the ignoreeof option (see set below) turned
          on.

     -- export [ name[=value] ] ...
          The given names are marked for automatic export to the environment
          of subsequently-executed commands.

     -- export -p
          When -p is specified, export will write to the standard the output
          names and values of all exported variables, in the following format:

             "export %s=%s\n",< name >, < value >

          The -p option allows portable access to the values that can be saved
          and then later restored using, for instance, a dot script.  The
          shell will format the output, including the proper use of quoting,
          so that it is suitable for reinput to the shell as commands that
          achieve the same exporting results.

     fc [ -e ename  ] [ -nlr ] [ first [ last ] ]
     fc -e - [ old=new ] [ command ]
     fc -s [ old=new ] [ first ]
          In the first form, a range of commands from first to last is
          selected from the last HISTSIZE commands that were typed at the
          terminal.  The arguments first and last may be specified as a
          [+]number or as a string.  A string is used to locate the most
          recent command starting with the given string.  A negative number is
          used as an offset to the current command number.  If the flag -l, is
          selected, the commands are listed on standard output.  Otherwise,
          the editor program ename is invoked on a file containing these
          keyboard commands.  If ename is not supplied, then the value of the
          variable FCEDIT (default /usr/bin/ed) is used as the editor.  When
          editing is complete, the edited command(s) is executed.  If last is
          not specified then it will be set to first.  If first is not
          specified the default is the previous command for editing and -16
          for listing.  The flag -r reverses the order of the commands and the
          flag -n suppresses command numbers when listing.  In the second form
          the command is re-executed after the substitution old=new is
          performed.  In the third form the command is re-executed after the
          substitution old=new is performed without invoking an editor.

     fg [ job... ]
          This command is only on systems that support job control.  Each job
          specified is brought to the foreground.  Otherwise, the current job
          is brought into the foreground.  See Jobs for a description of the
          format of job.

     getopts optstring name [ arg ... ]
          Checks arg for legal options.  If arg is omitted, the positional
          parameters are used.  An option argument begins with a + or a -.  An
          option not beginning with + or - or the argument -- ends the
          options.  optstring contains the letters that getopts recognizes.
          If a letter is followed by a :, that option is expected to have an
          argument.  The options can be separated from the argument by blanks.

          getopts places the next option letter it finds inside variable name
          each time it is invoked with a + prepended when arg begins with a +.
          The index of the next arg is stored in OPTIND.  The option argument,
          if any, gets stored in OPTARG.  Whenever the shell is invoked,
          OPTIND will be initialized to 1.

          A leading :  in optstring causes getopts to store the letter of an
          invalid option in OPTARG, and to set name to ?  for an unknown
          option and to :  when a required option is missing.  Otherwise,
          getopts prints an error message.  The exit status is non-zero when
          there are no more options.

     jobs [ -lnp ] [ job ... ]
          Lists information about each given job; or all active jobs if job is
          omitted.  The -l flag lists process ids in addition to the normal
          information.  The -n flag only displays jobs that have stopped or
          exited since last notified.  The -p flag causes only the process
          group to be listed.  See Jobs for a description of the format of
          job.

     kill [ -sig ] job ...
     kill -s signal_name  job ...
     kill -l [ exit_status ]
          Sends either the TERM (terminate) signal or the specified signal to
          the specified jobs or processes.  Signals are either given by number
          or by names (as given in /usr/include/signal.h, stripped of the
          prefix ``SIG'').  If the signal being sent is TERM (terminate) or
          HUP (hangup), then the job or process will be sent a CONT (continue)
          signal if it is stopped.  The argument job can the process id of a
          process that is not a member of one of the active jobs.  See Jobs
          for a description of the format of job.  In the third form, kill -l,
          the signal numbers and names are listed.  If an exit_status operand
          is given and it is the unsigned decimal integer value of a signal
          number, the signal_name (the specification-defined symbolic constant
          name without the ``SIG'' prefix) corresponding to that signal will
          be written.

     let arg ...
          Each arg is a separate arithmetic expression to be evaluated.  See
          Arithmetic Evaluation above, for a description of arithmetic
          expression evaluation.

          The exit status is 0 if the value of the last expression is non-
          zero, and 1 otherwise.

     - newgrp [-l] [ arg ]
     - newgrp [-] [ arg ]
          Equivalent to exec /usr/bin/newgrp arg.  The -l (ell) or the -
          option change the environment to what would be expected if the user
          actually logged in again.

     print [ -Rnprsu[n ] ] [ arg ... ]
          The shell output mechanism.  With no flags or with flag - or -- the
          arguments are printed on standard output as described by echo(1).
          In raw mode, -R or -r, the escape conventions of echo are ignored.
          The -R option will print all subsequent arguments and options other
          than -n.  The -p option causes the arguments to be written onto the
          pipe of the process spawned with |& instead of standard output.  The
          -s option causes the arguments to be written onto the history file
          instead of standard output.  The -u flag can be used to specify a
          one digit file descriptor unit number n on which the output will be
          placed.  The default is 1.  If the flag -n is used, no new-line is
          added to the output.

     pwd  Equivalent to print -r - $PWD

     read [ -prsu[ n ] ] [ name?prompt ] [ name ... ]
          The shell input mechanism.  One line is read and is broken up into
          fields using the characters in IFS as separators.  In raw mode, -r,
          a \ at the end of a line does not signify line continuation.  The
          first field is assigned to the first name, the second field to the
          second name, and so on, with leftover fields assigned to the last
          name.  The -p option causes the input line to be taken from the
          input pipe of a process spawned by the shell using |&.  If the -s
          flag is present, the input will be saved as a command in the history
          file.  The flag -u can be used to specify a one digit file
          descriptor unit to read from.  The file descriptor can be opened
          with the exec special command.  The default value of n is 0.  If
          name is omitted then REPLY is used as the default name.  The exit
          status is 0 unless an end-of-file is encountered.  An end-of-file
          with the -p option causes cleanup for this process so that another
          can be spawned.  If the first argument contains a ?, the remainder
          of this word is used as a prompt on standard error when the shell is
          interactive.  The exit status is 0 unless an end-of-file is
          encountered.

     -- readonly [ name[=value] ] ...
          The given names are marked readonly and these names cannot be
          changed by subsequent assignment.

     -- readonly -p
          When -p is specified, readonly will write to the standard the output
          names and values of all read-only variables, in the following
          format:

             "readonly %s=%s\n",< name >, < value >

          The -p option allows portable access to the values that can be saved
          and then later restored using, for instance, a dot script.  The
          shell will format the output, including the proper use of quoting,
          so that it is suitable for reinput to the shell as commands that
          achieve the same attribute-setting results.

     - return [ n ]
          Causes a shell function to return to the invoking script with the
          return status specified by n.  If n is omitted then the return
          status is that of the last command executed.  If return is invoked
          while not in a function or a script, then it is the same
e as an exit.

     - set [-abCefhkmnpstuvx] [-o option] [-A nam_
] [arg ... ]
          The flags for this command have meaning as follows:
          -A   Array assignment.  Unset the variable name and assign values
               sequentially from the list arg.  If +A is used, the variable
               name is not unset first.
          -a   All subsequent variables that are defined are automatically
               exported.
          -b   Cause the shell to notify the user asynchronously of background
               job completions. When the shell notifies the user a job has
               been completed, it may remove the job's process ID from the
               list of those known in the current shell execution environment.
               Asynchronous notification will not be enabled by default.
          -C   (Upper-case C) Prevent existing files from being overwritten by
               the shell's > redirection operator. The >| redirection operator
               will override this noclobber option for an individual file.
          -e   If a command has a non-zero exit status, execute the ERR trap,
               if set, and exit.  This mode is disabled while reading
               profiles.
          -f   Disables file name generation.
          -h   Each command becomes a tracked alias when first encountered.
          -k   All variable assignment arguments are placed in the environment
               for a command, not just those that precede the command name.
          -m   Background jobs will run in a separate process group and a line
               will print upon completion.  The exit status of background jobs
               is reported in a completion message.  On systems with job
               control, this flag is turned on automatically for interactive
               shells.
          -n   Read commands and check them for syntax errors, but do not
               execute them.  Ignored for interactive shells.
          -o   The following argument can be one of the following option
               names:
               allexport    Same as -a.
               errexit      Same as -e.
               bgnice       All background jobs are run at a lower priority.
                            This is the default mode.
               ignoreeof    The shell will not exit on end-of-file.  The
                            command exit must be used.
               keyword      Same as -k.
               markdirs     All directory names resulting from file name
                            generation have a trailing / appended.
               monitor      Same as -m.
               noclobber    Same as -C.
               noexec       Same as -n.
               noglob       Same as -f.
               nolog        Do not save function definitions in history file.
               notify       Same as -b.
               nounset      Same as -u.
               privileged   Same as -p.
               verbose      Same as -v.
               trackall     Same as -h.
               vi           Puts you in insert mode of a vi style in-line
                            editor until you hit escape character 033.  This
                            puts you in move mode.  A return sends the line.
               viraw        Each character is processed as it is typed in vi
                            mode.
               xtrace       Same as -x.
               If no option name is supplied then the current option settings
               are printed.
          -p   Disables processing of the $HOME/.profile file and uses the
               file /etc/suid_profile instead of the ENV file.  This mode is
               on whenever the effective uid (gid) is not equal to the real
               uid (gid).  Turning this off causes the effective uid and gid
               to be set to the real uid and gid.
          -s   Sort the positional parameters lexicographically.
          -t   Exit after reading and executing one command.
          -u   Treat unset parameters as an error when substituting.
          -v   Print shell input lines as they are read.
          -x   Print commands and their arguments as they are executed.
          -    Turns off -x and -v flags and stops examining arguments for
               flags.
          --   Do not change any of the flags; useful in setting $1 to a value
               beginning with -.  If no arguments follow this flag then the
               positional parameters are unset.

          Using + rather than - causes these flags to be turned off.  These
          flags can also be used upon invocation of the shell.  The current
          set of flags may be found in $-.  Unless -A is specified, the
          remaining arguments are positional parameters and are assigned, in
          order, to $1 $2 ....  If no arguments are given then the names and
          values of all variables are printed on the standard output.

     - shift [ n ]
           The positional parameters from $n+1 ...  are renamed $1 ...  ,
           default n is 1.  The parameter n can be any arithmetic expression
           that evaluates to a non-negative number less than or equal to $#.

     - times
           Print the accumulated user and system times for the shell and for
           processes run from the shell.

     - trap [ arg ] [ sig ] ...
           arg is a command to be read and executed when the shell receives
           signal(s) sig.  (Note that arg is scanned once when the trap is set
           and once when the trap is taken.)  Each sig can be given as a
           number or as the name of the signal.  Trap commands are executed in
           order of signal number.  Any attempt to set a trap on a signal that
           was ignored on entry to the current shell is ineffective.  If arg
           is omitted or is -, then all trap(s) sig are reset to their
           original values.  If arg is the null string then this signal is
           ignored by the shell and by the commands it invokes.  If sig is ERR
           then arg will be executed whenever a command has a non-zero exit
           status.  sig is DEBUG then arg will be executed after each command.
           If sig is 0 or EXIT and the trap statement is executed inside the
           body of a function, then the command arg is executed after the
           function completes.  If sig is 0 or EXIT for a trap set outside any
           function then the command arg is executed on exit from the shell.
           The trap command with no arguments prints a list of commands
           associated with each signal number.

     -- typeset [ _HLRZfilrtux[n] ]  [ name[ =value ]  ] ...
           Sets attributes and values for shell variables.  When invoked
           inside a function, a new instance of the variable name is created.
           The parameter value and type are restored when the function
           completes.  The following list of attributes may be specified:
           -H   This flag provides UNIX to host-name file mapping on non-UNIX
                machines.
           -L   Left justify and remove leading blanks from value.  If n is
                non-zero it defines the width of the field, otherwise it is
                determined by the width of the value of first assignment.
                When the variable is assigned to, it is filled on the right
                with blanks or truncated, if necessary, to fit into the field.
                Leading zeros are removed if the -Z flag is also set.  The -R
                flag is turned off.
           -R   Right justify and fill with leading blanks.  If n is non-zero
                it defines the width of the field, otherwise it is determined
                by the width of the value of first assignment.  The field is
                left filled with blanks or truncated from the end if the
                variable is reassigned.  The L flag is turned off.
           -Z   Right justify and fill with leading zeros if the first non-
                blank character is a digit and the -L flag has not been set.
                If n is non-zero it defines the width of the field, otherwise
                it is determined by the width of the value of first
                assignment.
           -f   The names refer to function names rather than variable names.
                No assignments can be made and the only other valid flags are
                -t, -u and -x.  The flag -t turns on execution tracing for
                this function.  The flag -u causes this function to be marked
                undefined.  The FPATH variable will be searched to find the
                function definition when the function is referenced.  The flag
                -x allows the function definition to remain in effect across
                shell procedures invoked by name.
           -i   Variable is an integer.  This makes arithmetic faster.  If n
                is non-zero it defines the output arithmetic base, otherwise
                the first assignment determines the output base.
           -l   All upper-case characters converted to lower-case.  The
                upper-case flag, -u is turned off.
           -r   The given names are marked readonly and these names cannot 
           -r   The given names are marked readonly and these names cannot be
                changed by subsequent assignment.
           -t   Tags the variables.  Tags are user definable and have no
                special meaning to the shell.
           -u   All lower-case characters are converted to upper-case
                characters.  The lower-case flag, -l is turned off.
           -x   The given names are marked for automatic export to the
                environment of subsequently-executed commands.

           Using + rather than - causes these flags to be turned off.  If no
           name arguments are given but flags are specified, a list of names
           (and optionally the values) of the variables which have these flags
           set is printed.  (Using + rather than - keeps the values from being
           printed.)  If no names and flags are given, the names and
           attributes of all variables are printed.

     ulimit [ -[HS][a | cdfnstvm] ]

     ulimit [ -[HS][c | d | f | n | s | t | v | m] ] limit
           ulimit prints or sets hard or soft resource limits.  These limits
           are described in getrlimit(2).

           If limit is not present, ulimit prints the specified limits.  Any
           number of limits may be printed at one time.  The -a option prints
           all limits.

           If limit is present, ulimit sets the specified limit to limit.  The
           string unlimited requests the largest valid limit.  Limits may be
           set for only one resource at a time.  Any user may set a soft limit
           to any value below the hard limit.  Any user may lower a hard
           limit.  Only a privileged user may raise a hard limit; see su(1).

           The -H option specifies a hard limit.  The -S option specifies a
           soft limit.  If neither option is specified, ulimit will set both
           limits and print the soft limit.

           The following options specify the resource whose limits are to be
           printed or set.  If no option is specified, the file size limit is
           printed or set.

           -c   maximum core file size (in 512-byte blocks)

           -d   maximum size of data segment or heap (in kbytes)

           -f   maximum file size (in 512-byte blocks)

           -n   maximum file descriptor plus 1

           -s   maximum size of stack segment (in kbytes).  Note that if this
                is set too high, sproc(2) may fail.

           -t   maximum CPU time (in seconds)

           -v   maximum size of virtual memory (in kbytes)

           -m   maximum size of resident memory (in kbytes)

           If no option is given, -f is assumed.

     umask [ -S ][ mask ]
           The user file-creation mask is set to mask [see umask(2)].  mask
           can either be an octal number or a symbolic value as described in
           chmod(1). If a symbolic value is given, the new umask value is the
           complement of the result of applying mask to the complement of the
           previous umask value.  If mask is omitted, the current value of the
           mask is printed.  If -S is specified, the symbolic output will be
           in the following format:

           "u=%s,g=%s,o=%s\n", owner, group, other

           where the three values will be permissions combinations of the
           letters from the set {r,w,x}.

     unalias name ...
     unalias -a
           The  variables given by the list of names are removed from the
           alias list. In the second form, all alias definitions are removed
           from the current shell execution environment.

     - unset [ -fv ] name ...
           The variables given by the list of names are unassigned, i. e.,
           their values and attributes are erased.  Read-only variables cannot
           be unset.  If the flag, -v, is set, then the names refer to
           variable names. This is the default when no options are specified.
           If the flag, -f, is set, then the names refer to function names.
           Unsetting ERRNO, LINENO, MAILCHECK, OPTARG
G, OPTIND, RANDOM,
           SECONDS, TMOUT, and _ causes removes their special meaning even if
           they are subsequently assigned to.  Unsetting variables not
           previously set or null returns a value of 0.

     - wait [ job ]
           Wait for the specified job and report its termination status.  If
           job is not given then all currently active child processes are
           waited for.  The exit status from this command is that of the
           process waited for.  See Jobs for a description of the format of
           job.

     whence [ -pv ] name ...
           For each name, indicate how it would be interpreted if used as a
           command name.

           -v   produces a more verbose report.

           -p   does a path search for name even if name is an alias, a
                function, or a reserved word.

   Invocation.
     If the shell is invoked by exec(2), and the first character of argument
     zero ($0) is -, then the shell is assumed to be a login shell and
     commands are read from /etc/profile and then from either .profile in the
     current directory or $HOME/.profile, if either file exists.  Next,
     commands are read from the file named by performing parameter
     substitution on the value of the environment variable ENV if the file
     exists.  If the -s flag is not present and arg is, then a path search is
     performed on the first arg to determine the name of the script to
     execute.  The script arg must have read permission and any setuid and
     setgid settings will be ignored.  Commands are then read as described
     below; the following flags are interpreted by the shell when it is
     invoked:
     -c string If the -c flag is present then commands are read from string.
     -s        If the -s flag is present or if no arguments remain then
               commands are read from the standard input.  Shell output,
               except for the output of the Special commands listed above, is
               written to file descriptor 2.
     -i        If the -i flag is present or if the shell input and output are
               attached to a terminal (as told by ioctl(2)) then this shell is
               interactive.  In this case TERM is ignored (so that kill 0 does
               not kill an interactive shell) and INTR is caught and ignored
               (so that wait is interruptible).  In all cases, QUIT is ignored
               by the shell.
     -r        If the -r flag is present the shell is a restricted shell.

     The remaining flags and arguments are described under the set command
     above.

   rksh Only.
     rksh is used to set up login names and execution environments whose
     capabilities are more controlled than those of the standard shell.  The
     actions of rksh are identical to those of sh, except that the following
     are disallowed:
          changing directory [see cd(1)],
          setting the value of SHELL, ENV, or PATH,
          specifying path or command names containing /,
          redirecting output (>, >| , <> , and >>).

     The restrictions above are enforced after .profile and the ENV files are
     interpreted.

     When a command to be executed is found to be a shell procedure, rksh
     invokes ksh to execute it.  Thus, it is possible to provide to the end-
     user shell procedures that have access to the full power of the standard
     shell, while imposing a limited menu of commands; this scheme assumes
     that the end-user does not have write and execute permissions in the same
     directory.

     The net effect of these rules is that the writer of the .profile has
     complete control over user actions, by performing guaranteed setup
     actions and leaving the user in an appropriate directory (probably not
     the login directory).

     The system administrator often sets up a directory of commands (that is,
     /usr/rbin) that can be safely invoked by rksh.

EXIT STATUS
     Errors detected by the shell, such as syntax errors, cause the shell to
     return a non-zero exit status.  Otherwise, the shell returns the exit
     status of the last command executed (see also the exit command above).
     If the shell is being used non-interactively then execution of the shell
     file is abandoned.  Run time errors detected by the shell are reported by
     printing the command or function name and the error condition.  If the
     line number that the error occurred on is greater than one, then the line
     number is also printed in square brackets ([]) after the command or
     function name.

     If a command is not found, the exit status will be 127.  If the command
     name is found, but it is not an executable utility, the exit status will
     be 126.  Applications that invoke utilities without using the shell
     should use these exit status values to report similar errors.

     If a command fails during word expansion or redirection, its exit status
     will be greater than zero.

     Internally, for purposes of deciding if a command exits with a non-zero
     exit status, the shell will recognise the entire status value retrieved
     for the command by the equivalent of the wait() function WEXITSTATUS
     macro. When reporting the exit status with the special parameter ?, the
     shell will report the full eight bits of exit status available. The exit
     status of a command that terminated because it received a signal will be
     reported as greater than 128.

FILES
     /etc/passwd
     /etc/profile
     /etc/suid_profile
     $HOME/.profile
     /tmp/sh*
     /dev/null

SEE ALSO
     cat(1), cd(1), chmod(1), cut(1), echo(1), env(1), paste
e(1), stty(1),
     test(1), umask(1), and vi(1)
     dup(2), exec(2), fork(2), ioctl(2), lseek(2), pipe
2), signal(2),
     umask(2), ulimit(2), wait(2), rand(3C), newgrp(1M)
 a.out(4), profile(4),
     environ(4)

     Morris I. Bolsky and David G. Korn, The KornShell Command and Programming
     Language, Prentice Hall, 1989

NOTES
     If a command which is a tracked alias is executed, and then a command
     with the same name is installed in a directory in the search path before
     the directory where the original command was found, the shell will
     continue to exec the original command.  Use the -t option of the alias
     command to correct this situation.

     Some very old shell scripts contain a ^ as a synonym for the pipe
     character.  |.

     Using the fc built-in command within a compound command will cause the
     whole command to disappear from the history file.
     The built-in command . file reads the whole file before any commands are
     executed.  Therefore, alias and unalias commands in the file will not
     apply to any functions defined in the file.

     Traps are not processed while a job is waiting for a foreground process.
     Thus, a trap on CHLD won't be executed until the foreground job
     terminates.










John Broxholme
Last modified: Tue Nov 24 13:12:17 GMT 1998