NAME
ksh, rksh − shell, the standard/restricted command programming language

SYNOPSIS
ksh [ −acefhikmnorstuvx ] [ −o option ] ... [ arg  ... ]
rksh [ −acefhikmnorstuvx ] [ −o option ] ... [ arg  ... ]

DESCRIPTION
Ksh is a command programming language that executes commands read from a terminal or a file.  Rksh is a restricted version of the command interpreter ksh, 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 aliases, functions, and named parameters. A word is a sequence of characters separated by one or more non-quoted metacharacters.

Commands
A simple-command is a sequence of blank-separated words that may be preceded by a parameter 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 (see 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 to terminate.

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.  Only one such command can be active at any given time.  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 can appear in a list, instead of semicolons, to delimit commands. 

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 for is executed, identifier is set to the next word taken from the in word list.  If in word ... is omitted, for executes the do list once for each positional parameter 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, 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, 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 parameter 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 identical to that used for file name generation (see File Name Generation below). 

if list then list [ elif list then list ] ... [ else 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, if returns a zero exit status. 

while list do list done

until 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, while 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.  If two adjacent open parentheses are needed for nesting, a space must be inserted to avoid arithmetic evaluation as described below.  A parenthesized list (for systems that support /dev/fd), used as a command argument, denotes process substitution as described below. 

{ list;} Execute list, but not in a separate environment. Note that { is a keyword and requires a trailing blank to be recognized. 

function identifier  { list ;}

identifier  () { list ;}
Define a function referred to by identifier. The body of the function is the list of commands between { and } (see Functions below). 

time pipeline The pipeline is executed and the elapsed time, the user time, and the system time are printed on standard error. 

The following keywords are recognized only 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.  The first character of an alias name can be any printable character, but the remaining characters must be identical to a valid identifier. The replacement string can contain any valid shell script, including the metacharacters listed above. The first word of each command of the replaced text is not tested for additional aliases. If the last character of the alias value is a blank, the word following the alias is also checked for alias substitution. Aliases can be used to redefine special built-in commands, but cannot be used to redefine the keywords 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 subshells 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 it to take effect, alias must be executed before the command referring to the alias is read. 

Aliases are frequently used as a shorthand for full path names.  An option to the aliasing facility allows the value of the alias to be automatically set to the full path name of the corresponding command.  These aliases are called tracked aliases.  The value of a tracked alias is defined the first time the identifier is read and becomes undefined each time the PATH variable is reset.  These aliases remain tracked so that the next reference will redefine the value.  Several tracked aliases are compiled into the shell.  The −h option of the set command converts each command name that is an identifier into a tracked alias. 

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

echo=′print −′

false=′let 0′

functions=′typeset −f′

history=′fc −l′

integer=′typeset −i′

nohup=′nohup ′

pwd=′print − $PWD′

r=′fc −e −′

true=′:′

type=′whence −v′

hash=′alias −t′

Tilde Substitution
After alias substitution is performed, each word is checked to see if it begins with an unquoted ~.  If it does, 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 are 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 ~, alone or before a /, is replaced by the value of the HOME parameter.  A ~ followed by a + or − is replaced by the value of the parameter PWD and OLDPWD, respectively. 

In addition, the value of each keyword parameter is checked to see if it begins with ~ or if ~ appears after :.  In either of these cases a tilde substitution is attempted. 

Command Substitution
The standard output from a command enclosed in parenthesis 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 $(<file). Command substitution of most special commands that do not perform input/output redirection are carried out without creating a separate process.

Process Substitution
This feature is available only on systems that support the /dev/fd directory for naming open files.  Each command argument of the form (list), <(list), or >(list) will run process list asynchronously connected to some file in /dev/fd.  The name of this file will become the argument to the command.  If the form with > is selected, writing on this file provides input for list. If < is used or omitted, the file passed as an argument will contain the output of the list process.  For example,

paste  (cut −f1 file1)  (cut −f3 file2) | tee >(process1)  >(process2)

cuts fields 1 and 3 from the files file1 and file2 respectively, pastes the results together, and sends it to the processes process1 and process2, as well as putting it onto the standard output. Because the file that is passed as an argument to the command is a pipe (see pipe(2)), programs that expect to use lseek(2) on the file will not work.

Parameter Substitution
A parameter is an identifier, one or more digits, or any of the characters ∗, @, #, ?, −, $, and !. A named parameter (a parameter denoted by an identifier) has a value and zero or more attributes.  Named parameters can be assigned values and attributes by using the typeset special command.  Attributes supported by ksh are described later with the typeset special command.  Exported parameters pass values and attributes to subshells but only values to the environment. 

The shell supports a limited one-dimensional array facility.  An element of an array parameter is referenced by a subscript.  A subscript is denoted by a [, followed by an arithmetic expression (see Arithmetic Evaluation below) followed by a ].  The value of all subscripts must be in the range of 0 through 511.  Arrays need not be declared.  Any reference to a named parameter with a valid subscript is legal and an array is created if necessary.  Referencing an array without a subscript is equivalent to referencing the first element. 

The value of a named parameter may also be assigned by writing:

name=value [ name=value ] ...

If the −i integer attribute is set for name, the value is subject to arithmetic evaluation as described below. 

Positional parameters, parameters denoted by a number, may be assigned values with the set special command.  Parameter $0 is set from argument zero when the shell is invoked. 

The character $ is used to introduce substitutable parameters.

${parameter} Substitute the value of the parameter, if any.  Braces are required when parameter is followed by a letter, digit, or underscore that should not be interpreted as part of its name or when a named parameter is subscripted.  If parameter is one or more digits, it is a positional parameter.  A positional parameter of more than one digit must be enclosed in braces.  If parameter is ∗ or @, all the positional parameters, starting with $1, are substituted (separated by a field separator character).  If an array identifier with subscript ∗ or @ is used, the value for each element is substituted (separated by a field separator character). 

${#parameter} If parameter is ∗ or @, the number of positional parameters is substituted.  Otherwise, the length of the value of the parameter is substituted. 

${#identifier[*]}
Substitute the number of elements in the array identifier.

${parameter:−word}
If parameter is set and is non-null, substitute its value; otherwise substitute word.

${parameter:=word}
If parameter is not set or is null, set it to word; then substitute the value of the parameter. Positional parameters may not be assigned in this way.

${parameter:?word}
If parameter is set and is non-null, substitute its value; otherwise, print word and exit from the shell.  If word is omitted, a standard message is printed. 

${parameter:+word}
If parameter is set and is non-null, substitute word; otherwise substitute nothing.

${parameter#pattern}

${parameter##pattern}
If the shell pattern matches the beginning of the value of parameter, the value of this substitution is the value of the parameter with the matched portion deleted; otherwise the value of this parameter is substituted.  In the former case, the smallest matching pattern is deleted; in the latter case, the largest matching pattern is deleted. 

${parameter%pattern}

${parameter%%pattern}
If the shell pattern matches the end of the value of parameter, the value of parameter with the matched part is deleted; otherwise substitute the value of parameter. In the former, the smallest matching pattern is deleted; in the latter, the largest matching pattern is deleted.

In the above, word is not evaluated unless it is used as the substituted string.  Thus, in the following example, pwd is executed only if d is not set or is null:

echo ${d:−`pwd`}

If the colon (:) is omitted from the above expressions, the shell only checks to determine whether or not parameter is set. 

The following parameters are set automatically by the shell:

# The number of positional parameters in decimal. 

− Flags supplied to the shell on invocation or by the set command. 

?  The decimal value returned by the last executed command. 

$ The process number of this shell. 

_ The last argument of the previous command.  This parameter is not set for commands which are asynchronous.  This parameter is also used to hold the name of the matching MAIL file when checking for mail.  Finally, the value of this parameter is set to the full path name of each program the shell invokes and is passed in the environment.

!  The process number of the last background command invoked. 

PPID The process number of the parent of the shell. 

PWD The present working directory set by the cd command. 

OLDPWD The previous working directory set by the cd command. 

RANDOM Each time this parameter is evaluated, a random integer is generated.  The sequence of random numbers can be initialized by assigning a numeric value to RANDOM. 

REPLY This parameter is set by the select statement and by the read special command when no arguments are supplied. 

SECONDS Each time this parameter is referenced, the number of seconds since shell invocation is returned.  If this parameter is assigned a value, the value returned upon reference will be the value that was assigned plus the number of seconds since the assignment. 

The following parameters are used by the shell:

CDPATH The search path for the cd command. 

COLUMNS If this variable is set, its value is used to define the width of the edit window for the shell edit modes and for printing select lists. 

EDITOR If the value of this variable ends in emacs, gmacs, or vi and the VISUAL variable is not set, the corresponding option is turned on.  (See set in Special Commands below.) 

ENV If this parameter is set, parameter substitution is performed on the value to generate the path name of the script to be executed when the shell is invoked.  (See Invocation below.)  This file is typically used for alias and function definitions. 

FCEDIT The default editor name for the fc command. 

IFS Internal field separators, normally space, tab, and new-line that are used to separate command words that result from command or parameter substitution and for separating words with the special command read.  The first character of the IFS parameter is used to separate arguments for the "$∗" substitution (see Quoting below). 

HISTFILE If this parameter is set when the shell is invoked, its value is the path name of the file that is used to store the command history.  (See Command Re-entry below.) 

HISTSIZE If this parameter is set when the shell is invoked, the number of previously entered commands accessible to this shell will be greater than or equal to this number.  The default is 128. 

HOME The default argument (home directory) for the cd command. 

LINES If this variable is set, the value is used to determine the column length for printing select lists.  Select lists print vertically until about two-thirds of LINES lines are filled. 

MAIL If this parameter is set to the name of a mail file and the MAILPATH parameter is not set, the shell informs the user of arrival of mail in the specified file. 

MAILCHECK This variable specifies how often (in seconds) the shell checks for changes in the modification time of any of the files specified by the MAILPATH or MAIL parameters.  The default value is 600 seconds.  When the time has elapsed the shell checks before issuing the next prompt. 

MAILPATH A list of file names separated by colons (:).  If this parameter is set, the shell informs the user of any modifications to the specified files that have occurred within the last MAILCHECK seconds.  Each file name can be followed by a ?  and a message to be printed, in which case the message will undergo parameter and command substitution with the parameter $_ defined as the name of the changed file.  The default message is you have mail in $_.

PATH The search path for commands (see Execution below).  The user may not change PATH if executing rksh (except in the .profile file). 

PS1 The value of this parameter is expanded for parameter substitution, to define the primary prompt string which, by default, is “$ ”. Replace the character !  in the primary prompt string is by the command number (see Command Re-entry below). 

PS2 Secondary prompt string, by default “> ”.

PS3 Selection prompt string used within a select loop, by default “#? ”.

SHELL The path name of the shell is kept in the environment.  When invoked, the shell is restricted if the value of this variable contains an r in the basename. 

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 Invokes the corresponding option when the value of this variable ends in emacs, gmacs, or vi. (See set in Special Commands below.) 

The shell gives default values to PATH, PS1, PS2, MAILCHECK, TMOUT  and IFS.  HOME, SHELL, ENV, and MAIL are never set automatically by the shell (although HOME is set by login(1)). On some systems, MAIL and SHELL are also set by login(1)).

Blank Interpretation
After parameter and command substitution, the results of substitution are scanned for field separator characters (found in IFS), and split into distinct arguments where such characters are found.  Ksh retains explicit null arguments ("" or ´´) but removes implicit null arguments (those resulting from parameters that have no values). 

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, the word is regarded as a pattern. The word is replaced with alphabetically sorted file names matching the pattern. If no file name is found that matches the pattern, the word is left unchanged. When a pattern is used for file name generation, the character .  at the beginning 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 !, any character not enclosed is matched.  A − can be included in the character set by using it as the first or last character. 

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 (i.e., made to stand for itself) by preceding it with a \.  The pair \new-line is ignored.  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 $@ is identical when not quoted or when used as a parameter assignment value or as a file name.  However, when used as a command argument, "$∗" is equivalent to "$1d$2d...", where d is the first character of the IFS parameter, whereas $@ is equivalent to "$1" "$2" .... Inside grave quote marks (``) \ quotes the characters \, `, and $.  If the grave quotes occur within double quotes, \ also quotes the character ". 

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

Arithmetic Evaluation
The ability to perform integer arithmetic is provided with the special command let.  Evaluations are performed using long arithmetic.  Constants take 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, base 10 is used. 

An internal integer representation of a named parameter can be specified with the −i option of the typeset special command.  When this attribute is selected the first parameter assignment parameter determines the arithmetic base 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 beginning with ((, all characters until the matching )) are treated as a quoted expression.  More precisely, (( ... )) is equivalent to let " ...". 

Prompting
When used interactively, the shell prompts with the 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, the secondary prompt (the value of PS2) is issued. 

Input/Output
Before a command is executed, its input and output can be redirected using a special notation interpreted by the shell. The following can 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 input (file descriptor 0). 

>word Use file word as standard output (file descriptor 1).  If the file does not exist, it is created; otherwise, it is truncated to zero length. 

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

<<[−]word The shell input is read up to a line that matches 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, 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 <<, all leading tabs are stripped from word and from the document. 

<&digit The standard input is duplicated from file descriptor digit (see dup(2)).

>&digit The standard output is duplicated to file descriptor digit (see dup(2)).

<&− The standard input is closed. 

>&− The standard output is closed. 

If one of the above is preceded by a digit, the file descriptor number cited 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. 

Redirection order is significant.  The shell evaluates each redirection in terms of the (file descriptor, file) assignment at the time of evaluation. For example:

... 1>fname 2>&1

first assigns file descriptor 1 to file fname. It then assigns file descriptor 2 to the file assigned to file descriptor 1 (that is, fname). If the order of redirection were reversed, file descriptor 2 would be assigned to the terminal (assuming file descriptor 1 had been) and then file descriptor 1 would be assigned to file fname.

If a command is followed by & and job control is inactive, 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 passed to an executed program much like a normal argument list. The names must be identifiers and the values are character strings.  The shell interacts with the environment in several ways.  When invoked, the shell scans the environment and creates a parameter for each name found, gives it the corresponding value and marks it export. Executed commands inherit the environment. If the user modifies the values of these parameters or creates new ones by using the export or typeset −x commands, the values 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 parameter assignments.  A parameter assignment argument takes the form identifier=value. For example,

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

are equivalent (as far as the above execution of cmd is concerned). 

If the −k flag is set, all parameter assignment arguments are placed in the environment, even if they occur after the command name.  The following echo statement prints a=b c.  After −k flag is set, the second echo statement prints only c:

echo a=b c
set −k
echo a=b c

Functions

The function keyword (described in the Commands section above) is used to define shell functions.  Shell functions are read 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.) 

Functions execute in the same process as the caller and share all files, traps (other than EXIT and ERR) and present working directory with the caller.  A trap set on EXIT inside a function is executed after the function completes.  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 option of the typeset special command.  The text of functions will also be listed.  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 reinvoking the shell.  Functions that must be defined across separate invocations of the shell should be placed in the ENV file. 

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 that looks like:

[1] 1234

indicating job number 1 was started asynchronously and had one (top-level) process whose process ID was 1234. 

(Note: this paragraph and the next describe job control features not available in all versions of HP-UX.)  On systems supporting job control, if you are running a job and wish to do something else, you can type ^Z (control-Z) to send a STOP signal to the current job.  The shell then indicates that the job has been ‘Stopped’, and print another prompt.  The user can then manipulate the state of this job by putting it in the background with the bg command, running other commands and eventually returning the job to the foreground with the fg command.  A ^Z takes effect immediately and resembles an interrupt, since pending output and unread input are discarded when ^Z is typed. 

A job run in the background stops if it tries to read from the terminal.  Background jobs normally are allowed to produce output, but can be disabled by giving the stty tostop command.  If the user sets this tty option, background jobs stop when trying to produce output. 

There are several ways to refer to jobs in the shell.  The character % introduces a job name.  If you wish to refer to job number 1, type %1.  Jobs are also named by prefixes of the string typed in to kill or restart them.  Thus, on systems that support job control, fg %ed normally restarts a suspended ed(1) job, if the name of the suspended job begins with the string ed. 

The shell maintains a notion of the current and previous jobs.  In output pertaining to jobs, the current job is marked with a + and the previous job with a −.  The abbreviation %+ refers to the current job and %− refers to the previous job.  %% is also a synonym for the current job. 

This shell learns immediately when a process changes state.  It informs the user when a job is blocked and prevented from further progress, but only just before it prints a prompt. 

If you try to leave the shell while jobs are running or stopped, you are warned, "You have stopped (running) jobs." You may use the jobs command to identify them.  If you immediately try to exit again, the shell will not warn you a second time, and the stopped jobs will be terminated. 

Signals
The INT and QUIT signals for an invoked command are ignored if the command is followed by & and job monitor option is not active.  Otherwise, signals have the values inherited by the shell from its parent, with the exception of signal 11 (but see also the trap command below). 

Execution
Substitutions are made each time a command is executed. If the command name matches one of the Special Commands listed below, it is executed within the current shell process.  Next, ksh checks the command name to determine whether it matches one of the user-defined functions.  If it does, ksh saves the positional parameters and resets to the arguments of the function call.  When the function completes or issues a return, ksh restores the positional parameter list and executes any trap set on EXIT within the function.  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, ksh creates a process and attempts to execute the command using exec(2).

The shell parameter PATH defines the search path for the directory containing the command.  Alternative directory names are separated by a colon (:).  The default path is /bin:/usr/bin: (specifying /bin, /usr/bin, and the current directory in that order).  Note that the current directory is specified by a null path name, which can appear immediately after the equal sign, between colon delimiters, or at the end of the path list.  The search path is not used if the command name contains a /.  Otherwise, each directory in the path is searched for an executable file.  If the file has execute permissions but is not a directory or an executable object code file, it is assumed to be a script file, which is a file of data for an interpreter.  If the first two characters of the script file are "#!", exec(2) expects an interpreter path name to follow. Exec(2) then attempts to execute the specified interpreter as a separate process to read the entire script file. If a call to exec(2) fails, /bin/ksh is spawned to interpret the script file.  All non-exported aliases, functions, and named parameters are removed in this case.  A parenthesized command is also executed in a subshell.  If the shell command file does not have read permission, or if the setuid and/or setgid bits are set on the file, the shell executes an agent to set up the permissions and execute the shell with the shell command file passed down as an open file.  A parenthesized command is also 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 HISTFILE variable is not set or writable.  A shell can access the commands of all interactive shells that use the same named HISTFILE.  The special command fc is used to list or edit a portion 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, the value of the parameter FCEDIT is used.  If FCEDIT is not defined, /bin/ed is used.  The edited command 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 parameter of the form old=new can be used to modify the command before execution.  For example, if r is aliased to ′fc −e −′ , typing ‘r bad=good c’ will re-execute the most recent command that starts with the letter c and replace the first occurrence of the string bad with the string good. 

In-line Editing Options
Normally, each command line typed at a terminal device is followed by a new-line (‘RETURN’ or ‘LINE FEED’). If either the emacs, gmacs, or vi option is set, the user can edit the command line.  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.  ADM terminal users should set the "space - advance" switch to ‘space’.  Hewlett-Packard terminal users should set the straps to ‘bcGHxZ etX’. 

The editing modes enable the user to look through a window at the current line.  The default window width is 80, unless the value of COLUMNS is defined.  If the line is longer than the window width minus two, a mark displayed at the end of the window notifies the user.  The mark is a > (<, *) if the line extends on the right (left, both) side(s) of the window.  As the cursor moves and reaches the window boundaries, the window is centered about the cursor. 

Emacs Editing Mode
This mode is invoked by either the emacs or gmacs option.  Their sole difference is their handling of ^T.  To edit, the user moves the cursor to the point needing correction and inserts or deletes characters or words.  All editing commands are control characters or escape sequences.  The notation for control characters is caret (^) followed by the character.  For example, ^F is the notation for control-F.  This is entered by depressing ‘f’ while holding down the ‘CTRL’ (control) key.  The ‘SHIFT’ key is not depressed.  (The notation ^?  indicates the DEL (delete) key.) 

The notation for escape sequences is M- followed by a character.  For example, M-f (pronounced Meta f) is entered by depressing ESC (ASCII 033) followed by ‘f’.  (M-F would be the notation for ESC followed by ‘SHIFT’ (capital) ‘F’.) 

All edit commands operate from any place on the line (not only at the beginning).  Neither the "RETURN" nor the "LINE FEED" key is entered after edit commands, except when noted. 

^F Move cursor forward (right) one character. 

M-f Move cursor forward one word.  (The editor’s idea of a word is a string of characters consisting of only letters, digits and underscores.) 

^B Move cursor backward (left) one character. 

M-b Move cursor backward one word. 

^A Move cursor to start of line. 

^E Move cursor to end of line. 

^]char Move cursor to character char on current line. 

^X^X Interchange the cursor and mark. 

erase (User defined erase character as defined by the stty(1) command, usually ^H or #.)  Delete previous character. 

^D Delete current character. 

eof End-of-file character, normally ^D, will terminate the shell if the current line is null. 

M-d Delete current word. 

M-^H (Meta-backspace) Delete previous word. 

M-h Delete previous word. 

M-^?  (Meta-DEL) Delete previous word (if your interrupt character is ^?  (DEL, the default) this command will not work). 

^T Transpose current character with next character in emacs mode.  Transpose two previous characters in gmacs mode. 

^C Capitalize current character. 

M-C Capitalize current word. 

M-l Change the current word to lowercase. 

^K Kill from the cursor to the end of the line.  If given a parameter of zero, kill from the start of line to the cursor. 

^W Kill from the cursor to the mark. 

M-p Push the region from the cursor to the mark on the stack. 

kill (User-defined kill character, as defined by the stty(1) command, usually ^G or @.)  Kill the entire current line.  If two kill characters are entered in succession, all subsequent consecutive kill characters cause a line feed (useful when using paper terminals). 

^Y Restore last item removed from line. (Yank item back to the line.) 

^L Line feed and print current line. 

^@ (Null character) Set mark. 

M- (Meta space) Set mark. 

^J (New line)  Execute the current line. 

^M (Return)  Execute the current line. 

^P Fetch previous command.  Each time ^P is entered, the previous command in the history list is accessed. 

^N Fetch next command.  Each time ^N is entered the next command in the history list is accessed. 

M-< Fetch the least recent (oldest) history line. 

M-> Fetch the most recent (youngest) history line. 

^Rstring Reverse search history for a previous command line containing string. If a parameter of zero is given, the search is forward. String is terminated by a "RETURN" or "NEW LINE".  If string is omitted, the next command line containing the most recent string is accessed.  In this case a parameter of zero reverses the direction of the search. 

^O Operate − Execute the current line and fetch the next line relative to current line from the history file. 

M-digits (Escape) Define numeric parameter, the digits are taken as a parameter to the next command.  The commands that accept a parameter are ., ^F, ^B, erase, ^D, ^K, ^R, ^P, ^N, M-., M-_, M-b, M-c, M-d, M-f, M-h and M-^H. 

M-letter Soft-key − Your alias list is searched for an alias by the name _letter and if an alias of this name is defined, its value is inserted on the input queue.  The letter must not be one of the above meta-functions. 

M-.  The last word of the previous command is inserted on the line.  If preceded by a numeric parameter, the value of this parameter determines which word to insert rather than the last word. 

M-_ Same as M-.. 

M-* Attempt file name generation on the current word. 

M-ESC Attempt file name completion on the current word. 

M-= List files matching current word pattern as if an asterisk were appended. 

^U Multiply parameter of next command by 4. 

\ Escape next character.  Editing characters, the user’s erase, kill and interrupt (normally ^?) characters may be entered in a command line or in a search string if preceded by a \.  The \ removes the next character’s editing features (if any). 

^V Display version of the shell. 

Vi Editing Mode
There are two typing modes. Entering a command puts you into input mode.  To edit, the user enters control mode by typing ESC (033) and moves the cursor to the point needing correction, then inserts or deletes characters or words.  Most control commands accept an optional repeat count prior to the command. 

In vi mode on most systems, canonical processing is initially enabled and the command is echoed again if the speed is 1200 baud or greater and contains any control characters, or if 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. 

Setting the viraw option will always disable canonical processing on the terminal.  This mode is implicit for systems that do not support two alternate end-of-line delimiters, and may be helpful for certain terminals. 

     Input Edit Commands

By default the editor is in input mode. 

erase Delete previous character.  (Erase is a user-defined erase character, as defined by the stty(1) command, usually ^H or #.) 

^W Delete the previous blank separated word. 

^D Terminate the shell. 

^V Escape next character.  Editing characters, erase or kill characters may be entered in a command line or in a search string if preceded by a ^V.  ^V removes the next character’s editing features (if any). 

\ Escape the next erase or kill character. 

     Motion Edit Commands
These commands move the cursor.  The designation [count] causes a repetition of the command the cited number of times.

[count]l Cursor forward (right) one character. 

[count]w Cursor forward one alphanumeric 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]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. 

; Repeats the last single character find command, f, F, t, or T. 

, Reverses the last single character find command. 

0 Cursor to start of line. 

^ Cursor to first nonblank 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 next earlier command in the history list is accessed. 

[count]− Equivalent to k. 

[count]j Fetch next command.  Each time j is entered, the next later command in the history list is accessed. 

[count]+ Equivalent to j. 

[count]G The command number count is fetched.  The default is the first command in the history list. 

/string Search backward through history for a previous command containing string. String is terminated by a "RETURN" or "NEW-LINE".  If string is null, the previous string is used. 

?string Same as / but search 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 Move cursor to the character position specified by motion, deleting all characters between the original cursor position and new position, and enter input mode. If motion is c, the entire line is 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 Move cursor to the character position specified by motion, deleting all characters between the original cursor position and new position.  Equivalent to d$.  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 the two character sequence ^i. 

[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. 

rc Replace the current character with c.

[count]x Delete current character. 

[count]X Delete preceding character. 

[count]. Repeat the previous text modification command. 

~ Invert the case of the current character and advance the cursor. 

[count]_ Causes the count word of the previous command to be appended at the current cursor location and places the editor in input mode at the end of the appended text.  The last word is used if count is omitted. 

* Appends an * to the current word and attempts file name generation.  If no match is found, the bell rings.  If a match is found, the word is replaced by the matching string and the command places the editor in input mode. 

ESC Attempt file name completion on the current word. 

     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:−vi}} count in the input buffer.  If count is omitted, 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. 

# Equivalent to I#<cr>.  Sends the line after inserting a # in front of the line and after each new-line.  Useful for inserting the current command line in the history list without executing it. 

= List the filenames that match the current word if an asterisk were appended to it. 

@letter The user’s alias list is searched for an alias by the name _letter and if an alias of this name is defined, its value is inserted on the input queue for processing. 

Special Commands
The following simple-commands are executed in the shell process. They permit input/output redirection. File descriptor 1 is the default output location. Commands that are preceded by † or †† are treated specially in the following ways:

1.  Parameter assignment lists preceding the command remain in effect when the command completes. 

2.  They are executed in a separate process when used within command substitution. 

3.  Errors in commands preceded by †† cause the script that contains them to abort. 

† : [ arg ... ] The command only expands parameters.  A zero exit code is returned. 

†† . file [ arg ...
Read and execute commands from file and return.  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. 

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 path name corresponding to the given name. The value becomes undefined when the value of PATH is reset but the aliases remained 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 across sub-shell environments.  Alias returns true unless a name is given for which no alias has been defined. 

bg [ %job ] This command is found only on systems that support job control.  Puts the specified job into the background.  The current job is put in the background if job is unspecified. 

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

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

† cd [ arg ]

† cd  old new This command can take 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 parameter HOME is the default arg. The parameter PWD is set to the current directory.  The shell parameter CDPATH defines the search path for the directory containing arg. Alternative directory names are separated by a colon (:).  If CDPATH is null or undefined, the default value is 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 /, 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 will not be executed by rksh.

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

†† eval [ arg ... ]
Reads the arguments as input to the shell and executes the resulting command(s).

†† exec [ arg ... ]
Parameter assignments remain in effect after the command completes. 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 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, the exit status is that of the last command executed.  An end-of-file also causes the shell to exit, except when a shell has the ignoreeof option set. (See set below.) 

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

†† fc [ −e ename  ] [ −nlr ] [ first [ last ] ]

†† fc −e −  [ old=new ] [ command ]
In the first form, a range of commands from first to last is selected from the last HISTSIZE commands typed at the terminal.  The arguments first and last may be specified as a number or string.  A given string is used to locate the most recent command.  A negative number is used to offset the current command number.  The flag −l causes the commands to be listed on standard output.  Otherwise, the editor program ename is invoked on a file containing these keyboard commands.  If ename is not supplied, the value of the parameter FCEDIT (default /bin/ed) is used as the editor.  Once editing has ended, the commands (if any) are executed.  If last is omitted, only the command specified by first will be used.  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 latter, the command is re-executed after the substitution old=new is performed.

fg [ %job ] This command is found only on systems that support job control.  If job is specified it brings it to the foreground.  Otherwise, the current job is brought into the foreground. 

jobs [ −l ] Lists the active jobs; the −l option lists process IDs also. 

kill [ −sig ] process ...
Sends either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are given either by number or name (as given in signal(2), stripped of the prefix “SIG”). The signal names are listed by kill −l.  No default exists; merely typing kill does not affect the current job.  If the signal being sent is TERM (terminate) or HUP (hangup), the job or process will be sent a CONT (continue) signal when stopped.  The process argument can be either a process ID or job. 

let  arg ... Each arg is an arithmetic expression to be evaluated.  All calculations are done as long integers and no check for overflow is performed.  Expressions consist of constants, named parameters, and operators.  The following set of operators, listed in order of decreasing precedence, have been implemented:

− unary minus

!  logical negation

*  /  % multiplication, division, remainder

+  − addition, subtraction

<=  >=  <  >
comparison

==  != equality  inequality

= arithmetic replacement

Sub-expressions in parentheses () are evaluated first and can be used to override the above precedence rules.  The evaluation within a precedence group is from right to left for the = operator and from left to right for the others. 

A parameter name must be a valid identifier. When a parameter is encountered, the value associated with the parameter name is substituted and expression evaluation resumes. Up to nine levels of recursion are permitted.

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

†† newgrp [ arg ... ]
Equivalent to exec newgrp arg ....

print [ −Rnprsu[n ]  ] [ arg ... ]
The shell output mechanism. With no flags or with flag −, the arguments are printed on standard output as described by echo(1). Raw mode, −R or −r, ignores the escape conventions of echo. 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 words using the characters in IFS as separators.  In −r raw mode, \ at the end of a line does not signify line continuation.  The first word is assigned to the first name, the second word to the second name, etc., with remaining words 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, REPLY is used as the default name.  The return code 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 process can be spawned.  If the first argument contains a ?, the remainder of this word is used as a prompt when the shell is interactive.  If the given file descriptor is open for writing and is a terminal device, the prompt is placed on this unit.  Otherwise the prompt is issued on file descriptor 2.  The return code is 0, unless an end-of-file is encountered. 

†† readonly [ name ... ]
The given names are marked read only and these names cannot be changed by subsequent assignment. 

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

set [ −aefhkmnostuvx ] [ −o option ] [ arg ... ]
The flags for this command are used as follows:

−a All subsequent defined parameters are automatically exported. 

−e If the shell is non-interactive and if a command fails, execute the ERR trap, if set, and exit immediately.  This mode is disabled while reading profiles. 

−f Disables file name generation. 

−h Each command whose name is an identifier becomes a tracked alias when first encountered. 

−k All parameter assignment arguments (not just those that precede the command name) are placed in the environment for a command. 

−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 but do not execute them.  The −n option is ignored for interactive shells. 

−o The −o argument takes any of several option names, but only one option can be specified at a time.  If none is supplied, the current option settings are printed.  The −o argument options follow:

allexport Same as −a. 

bgnice All background jobs are run at a lower priority. 

errexit Same as −e. 

emacs Puts you in an emacs style in-line editor for command entry. 

gmacs Puts you in a gmacs style in-line editor for command entry. 

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. 

noexec Same as −n. 

noglob Same as −f. 

nounset Same as −u. 

protected 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. 

−p Resets the PATH variable to the default value, disables processing of the $HOME/.profile file and uses the file /etc/suid_profile instead of the ENV file.  This mode is automatically enabled whenever the effective uid (gid) is not equal to the real uid (gid). 

−s Sort the positional parameters. 

−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, 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 $−.  The remaining arguments are positional parameters and are assigned consecutively to
$1, $2, .... If no arguments are given, the values of all names 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 $#. 

test [ expr ] Evaluate conditional expression expr. See test(1) for usage and description. The arithmetic comparison operators are not restricted to integers. They allow any arithmetic expression. Four additional primitive expressions are allowed:

−L file True if file is a symbolic link. 

file1 −nt file2 True if file1 is newer than file2.

file1 −ot file2 True if file1 is older than file2.

file1 −ef file2 True if file1 has the same device and i-node number as file2.

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 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 name of the signal.  Trap commands are executed signal number order.  Any attempt to set a trap on a signal that was ignored upon entering the current shell is ineffective.  If arg is omitted or is −, all traps for sig are reset to their original values.  If arg is the null string, this signal is ignored by the shell and by the commands it invokes.  If sig is ERR, arg will be executed whenever a command has a non-zero exit code.  This trap is not inherited by functions.  If sig is 0 or EXIT and the trap statement is executed inside the body of a function, the command arg is executed after the function completes.  If sig is 0 or EXIT for a trap set outside any function, 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 [ −HLRZefilprtux[n ] [ name[ =value ] ]  ... ]
Parameter assignments remain in effect after the command completes. When invoked inside a function, a new instance of the parameter name is created.  The parameter value and type are restored when the function completes.  The following list of attributes may be specified:

−H Provide HP-UX to host-name file mapping on non-UNIX machines. 

−F Provide HP-UX 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 name is assigned, the value 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 parameter 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. 

−e Tag the parameter as having an error.  This tag is currently unused by the shell and can be set or cleared by the user. 

−f Cause name to refer to function names rather than parameter names.  No assignments can be made to the name declared with the typeset statement.  The only other valid flags are −t (which turns on execution tracing for this function) and −x (which allows the function to remain in effect across shell procedures executed in the same process environment). 

−i Parameter 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 Convert all uppercase characters to lowercase.  The uppercase −u flag is turned off. 

−p Write the output of this command, if any, onto the two-way pipe. 

−r Any given name is marked "read only" and cannot be changed by subsequent assignment. 

−t Tag the named parameters.  Tags are user definable and have no special meaning to the shell. 

−u Convert all lowercase characters to uppercase characters.  The lowercase −l flag is turned off. 

−x Mark any given name 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 parameters that have these flags set is printed.  (Using + rather than − retains the values to be printed.)  If no names and flags are given, the names and attributes of all parameters are printed. 

ulimit [ −acdfmpst ] [ n ]

−a List all of the current resource limits (BSD only). 

−c Impose a size limit of n 512 byte blocks on the size of core dumps (BSD only). 

−d Impose a size limit of n kbytes on the size of the data area (BSD only). 

−f Impose a size limit of n 512 byte blocks on files written by child processes (files of any size may be read). 

−m Impose a soft limit of n kbytes on the size of physical memory (BSD only). 

−p Change the pipe size to n (UNIX/RT only). 

−s Impose a size limit of n kbytes on the size of the stack area (BSD only). 

−t Impose a time limit of n seconds to be used by each process (BSD only). 

If no option is given, −f is assumed.  If n is not given, the current limit is printed. 

umask [ nnn ] The user file-creation mask is set to nnn (see umask(2)). If nnn is omitted, the current value of the mask is printed. 

unalias name ...
The parameters given by the list of names are removed from the alias list. 

unset [ −f ] name ...
The parameters given by the list of names are unassigned; that is, their values and attributes are erased. Read-only variables cannot be unset. If the −f flag is set, names refer to function names. 

wait [ n ] Wait for the specified process to terminate or stop, and report its status.  This status becomes the return code for the wait command.  If n is not given, wait waits for all currently active child processes to terminate or stop.  The termination status returned is that of the last process. 

whence [ −v ] name ...
For each name, indicate how it would be interpreted if used as a command name.
The −v flag produces a more verbose report. 

Invocation of ksh
If the shell is invoked by exec(2), and the first character of argument zero ($0) is −, the shell is assumed to be a login shell and commands are read first from /etc/profile, 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 parameter ENV, if the file exists.  If the −s flag is not present and arg is, a path search is performed on the first arg to determine the name of the script to execute.  When running ksh with arg, the script arg must have read permission and any setuid and getgid 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, commands are read from string.

−s If the −s flag is present or if no arguments remain, commands are read from the standard input.  Shell output, except for the output of some 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 reported by tty(3C)), the shell is interactive. In this case SIGTERM is ignored (so that kill 0 does not kill an interactive shell) and SIGINT is caught and ignored (so that wait is interruptible).  In all cases, SIGQUIT is ignored by the shell.  (See signal(2).)

−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 where capabilities are more controlled than those of the standard shell.  The actions of rksh are identical to those of ksh, except that the following are forbidden:

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, the end-user is provided with shell procedures accessible to the full power of the standard shell, while being restricted to a limited menu of commands.  This scheme assumes that the end-user does not have write and execute permissions in the same directory. 

These rules effectively give the writer of the .profile file complete control over user actions, by performing guaranteed set-up actions and leaving the user in an appropriate directory (probably not the login directory). 

The system administrator often sets up a directory of commands (usually /usr/rbin) that can be safely invoked by rksh. HP-UX systems provide a restricted editor red (see ed(1)), suitable for restricted users.

RETURN VALUE
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 (also see the exit command above).  If the shell is being used non-interactively, execution of the shell file is abandoned.  Runtime errors detected by the shell are reported by printing the command or function name and the error condition.  If the line number on which the error occurred is greater than one, the line number is also printed in brackets ([]) after the command or function name. 

WARNINGS

If a command which is a tracked alias is executed, and 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 load and execute the original command.  Use the −t option of the alias command to correct this situation. 

If you move the current directory or one above it, pwd may not give the correct response.  Use the cd command with a full path name to correct this situation. 

Some very old shell scripts contain a caret (^) as a synonym for the pipe character (│).  Note however, ksh does not recognize the caret as a pipe character. 

If a command is piped into a shell command, all variables set in the shell command are lost when the command completes. 

Using the fc built-in command within a compound command will cause the entire command to disappear from the history file. 

The built-in command . file reads the entire file before any commands are executed. Therefore, alias and unalias commands in the file will not apply to any functions defined in the file. 

The export built-in command does not handle arrays properly.  Only the first element of an array is exported to the environment.

Background processes started from a non-interactive shell cannot be accessed by using job control commands. 

DEPENDENCIES

Series 300
Job control is not supported.

AUTHOR
Ksh was developed by AT&T. 

FILES

/etc/passwd to find home directories

/etc/profile read to set up system environment

/etc/suid_profile security profile

$HOME/.profile read to set up user’s custom environment

/tmp/sh∗ for here-documents

SEE ALSO
cat(1), cd(1), echo(1), env(1), test(1), umask(1), vi(1), dup(2), exec(2), fork(2), gtty(2), pipe(2), signal(2), umask(2), ulimit(2), wait(2), rand(3C), a.out(4), profile(4), environ(5).

Hewlett-Packard Company  —  May 11, 2021