KSH(1) BSD KSH(1)
NAME
ksh - the Korn shell command programming language
SYNOPSIS
ksh [ -aefhikmnoprstuvx ] [ -o option ] . . . [ -c string ]
[ -D name=val . . . ] [ arg . . . ]
DESCRIPTION
ksh is a command programming language that executes commands read from a
terminal or a file. See Invocation below for the meaning of arguments to
the shell. rksh is the restricted version of this shell. rksh is used to
set up login names and execution environments whose capabilities are more
controlled than those of the standard 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 which 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(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 (i.e., 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 may 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 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 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 the same as 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, then
the if command 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, 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. A parenthesized
list used as a command argument denotes process substitution as
described below.
{ list;}
list is simply executed. Note that { is a keyword and requires a
blank in order to be recognized.
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).
time pipeline
The pipeline is executed and the elapsed time as well as the user
and system time are printed on standard error.
The following keywords 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. The first character of an alias
name can be any non-special printable character, but the rest of the
characters must be the same as for 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 will
not be tested for additional 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 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 sub-shells 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 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 command name which is a valid alias
name into a tracked alias.
The following exported aliases are compiled into the shell but can be
unset or redefined:
false='let 0'
functions='typeset -f'
history='fc -l'
integer='typeset -i'
nohup='nohup '
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, 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 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 a ~ or if a ~ appears after a :. 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.
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. The attributes supported by the shell are described
later with the typeset special command. Exported parameters pass values
and attributes to sub-shells 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 will be 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 integer attribute, -i, 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}
The value, if any, of the parameter is substituted. The braces are
required when parameter is followed by a letter, digit, or
underscore that is not to be interpreted as part of its name or when
a named parameter is subscripted. If parameter is one or more
digits then it is a positional parameter. A positional parameter of
more than one digit must be enclosed in braces. If parameter is *
or @, then all the positional parameters, starting with $1, are
substituted (separated by a field separator character). If an array
identifier with subscript * or @ is used, then the value for each of
the elements 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[*]}
The number of elements in the array identifier is substituted.
${parameter:-word}
If parameter is set and is non-null then substitute its value;
otherwise substitute word.
${parameter:=word}
If parameter is not set or is null then set it to word; the value of
the parameter is then substituted. Positional parameters may not be
assigned to in this way.
${parameter:?word}
If parameter is set and is non-null then substitute its value;
otherwise, print word and exit from the shell. If word is omitted
then a standard message is printed.
${parameter:+word}
If parameter is set and is non-null then substitute word; otherwise
substitute nothing.
${parameter#pattern}
${parameter##pattern}
If the shell pattern matches the beginning of the value of
parameter, then 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 first form the smallest
matching pattern is deleted and in the latter form the largest
matching pattern is deleted.
${parameter%pattern}
${parameter%%pattern}
If the shell pattern matches the end of the value of parameter, then
the value of parameter with the matched part deleted; otherwise
substitute the value of parameter. In the first form the smallest
matching pattern is deleted and in the latter form the largest
matching pattern is deleted.
In the above, word is not evaluated unless it is to be used as the
substituted string, so that, 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, then the shell
only checks whether parameter is set or not.
The following parameters are automatically set 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 pathname 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 referenced, 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, then 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, the 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, then the corresponding option
(see Special Command set below) will be turned on. This value
should be unset for shells running in Apollo transcript pads.
ENV If this parameter is set, then parameter substitution is
performed on the value to generate the pathname of the script
that will 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. In Apollo
transcript pads, this variable should be set to 'pad'. On
dialup lines or in VT100 windows, values like 'vi' or 'emacs'
are useful.
IFS Internal field separators, normally space, tab, and new-line
that is used to separate command words which 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, then the
value is the pathname of the file that will be used to store
the command history. (See Command Re-entry below.)
HISTSIZE
If this parameter is set when the shell is invoked, then the
number of previously entered commands that are accessible by
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 will
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, then the shell informs the user
of arrival of mail in the specified file.
MAILCHECK
This variable specifies how often (in seconds) the shell will
check 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 will
check before issuing the next prompt.
MAILPATH
A colon ( : ) separated list of file names. If this parameter
is set then 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 that will be printed. The message will undergo
parameter and command substitution with the parameter, $_
defined as the name of the file that has changed. The default
message is you have mail in $_.
PATH The search path for commands (see Execution below). The user
may not change PATH if executing under rksh (except in
.profile).
PS1 The value of this parameter is expanded for parameter
substitution to define the primary prompt string which by
default is ``$ ''. The character ! in the primary prompt
string is replaced 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 pathname of the shell is kept in the environment. This
value should be unset for shells running in Apollo transcript
pads.
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 emacs, gmacs, or vi then
the corresponding option (see Special Command set below) will
be turned on.
The shell gives default values to PATH, PS1, PS2, MAILCHECK, TMOUT and
IFS, while HOME, SHELL ENV and MAIL are not set at all 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 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 alphabetically 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.
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 then \ 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
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 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 assignment to the parameter determines the
arithmetic base to be 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 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 (i.e., the
value of PS2) is issued.
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 input (file descriptor 0).
>word Use file word as standard output (file descriptor 1). If
the file does not exist then it is created; otherwise, it
is truncated to zero length.
>>word Use file word as standard output. If the file exists then
output is appended to it; otherwise, the file is created.
<<[-]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 >&-.
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 (i.e.
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(7)) 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 parameter 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 parameters 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 parameter assignments. A parameter
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).
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 first prints a=b c and then 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 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).
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 a separate invocation of the shell.
Functions that need to 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 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.
This paragraph and the next require features that are not in all versions
of UNIX and may not apply. If you are running a job and wish to do
something else you can press CTRL/Z (control-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. The character %
introduces a job name. If you wish to refer to job number 1, you can
name it as %1 . Jobs can also be named by prefixes of the string typed in
to kill or restart them. Thus, on systems that support job control, `fg
%ed' would normally restart a suspended ed(1) job, if there were a
suspended job whose name began 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 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 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
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
(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 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). 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 named parameters are removed in this
case. If the shell command file doesn't have read permission, or if the
setuid and/or setgid bits are set on the file, then the shell executes an
agent whose job it is 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 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 parameter FCEDIT is used. If FCEDIT is not defined then /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 parameter 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 either the
emacs, gmacs, or vi option is active, the user can edit the command line.
To be in either of these edit modes set the corresponding 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. ADM terminal users should set the
"space - advance" switch to `space'. Hewlett-Packard series 2621
terminal users should set the straps to `bcGHxZ etX'.
The editing modes implement 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 in-line editing options are not useful in Apollo transcript pads.
The command input pane associated with transcript pads allows full
command line editing. Setting VISUAL or EDITOR in Apollo transcript pads
causes the pad to flip in and out of raw mode.
In-Line editing is very useful on dialup UP terminals or in a VT100
window where no other editing is available.
Emacs Editing Mode
This mode is entered by enabling either the emacs or gmacs option. The
only difference between these two modes is the way they handle ^T. To
edit, the user moves the cursor to the point needing correction and then
inserts or deletes characters or words as needed. All the 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 pressing
`f' while holding down the `CTRL' (control) key. The `SHIFT' key is not
pressed. (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 just 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 command,
usually ^H or #.) Delete previous character.
^D Delete current character.
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) then 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 lower case.
^K Kill from the cursor to the end of the line. If given a
parameter of zero then 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 command,
usually ^G or @.) Kill the entire current line. If two kill
characters are entered in succession, all kill characters from
then on 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.
eof End-of-file character, normally ^D, will terminate the shell if
the current line is null.
^P Fetch previous command. Each time ^P is entered the previous
command back in time is accessed.
M-< Fetch the least recent (oldest) history line.
M-> Fetch the most recent (youngest) history line.
^N Fetch next command. Each time ^N is entered the next command
forward in time is accessed.
^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, then 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 will
be 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. An asterisk
is appended if the word doesn't contain any special pattern
characters.
M-ESC Same as M-*.
M-= List files matching current word pattern 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. 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
than 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. 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 (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]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 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 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$.
[count]dmotion
d[count]motion
Delete current character through the character that motion
would move to. If motion is d , the entire line will be
deleted.
i Enter input mode and insert text before the current
character.
I Insert text before the beginning of the line. Equivalent
to the two character sequence ^i.
[count]P Place the previous text modification before the cursor.
[count]p Place the previous text modification after the cursor.
R Enter input mode and replace characters on the screen with
characters you type overlay fashion.
rc Replace the current character with c.
[count]x Delete current character.
[count]X Delete preceding character.
[count]. Repeat the previous text modification command.
~ Invert the case of the current character and advance the
cursor.
[count]_ Causes the count word of the previous command to be
appended and input mode entered. The last word is used if
count is omitted.
* Causes an * to be appended to the current word and file
name generation attempted. If no match is found, it rings
the bell. Otherwise, the word is replaced by the matching
pattern and input mode is entered.
Other Edit Commands
[count]ymotion
y[count]motion
Yank current character through character that motion would
move the cursor to and puts them into the delete buffer.
The text and cursor are unchanged.
Y Yanks from current position to end of line. Equivalent to
y$.
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, 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
and after each new-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.
Input/Output redirection is permitted. Unless otherwise indicated, the
output is written on file descriptor 1. Commands that are preceded by
one or two | 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 pathname 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 only built-in on systems that support job control.
Puts the specified job into the background. The current job is put
in the background if job is not specified.
break [ n ]
Exit from the enclosing for while until or select loop, if any. If
n is specified then break n levels.
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 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 (:). The default path is <null> (specifying the current
directory). Note that the current directory is specified by a null
pathname, 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 ... ]
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 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 parameter
FCEDIT (default /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.
fg [ %job ]
This command is only built-in 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.
inlib pathname
Install a user-supplied library specified by pathname in the current
(shell) process. The library is used to resolve external references
of programs (and libraries) loaded after its installation. Note
that the library is not loaded into the address space unless it is
needed to resolve an external reference. The list of inlibed
libraries is passed to all children of the current shell. Use
llib(1) to examine this list.
jobs [ -l ]
Lists the active jobs; given the -l options lists process id's in
addition to the normal information.
kill [ -sig ] process ...
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"). The signal numbers and names are listed by 'kill
-l'. 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 process can be either a process id or a
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).
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
words 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 word is assigned to the first name, the second word to the
second name, etc., with leftover 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
then 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 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 then 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 readonly 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 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 as an exit.
rootnode [arg]
Change the current node entry directory to arg.
set [ -aefhkmnostuvx ] [ -o option ... ] [ arg ... ]
The flags for this command have meaning as follows:
-a All subsequent parameters that are defined 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 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 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.
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.
are printed.
If no option name is supplied then the current option settings
-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
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 $-. The remaining arguments are
positional parameters and are assigned, in order, to $1 $2 .... If
no arguments are given, then 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 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 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, 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 [ -HLRZfilprtux[n ] [ name[ =value ] ] ... ]
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 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 parameter 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
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.
-f The names refer to function names rather than parameter names.
No assignments can be made and the only other valid flags are
-t, which turns on execution tracing for this function and -x,
to allow 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 All upper-case characters converted to lower-case. The upper-
case flag, -u is turned off.
-p The output of this command, if any, is written onto the two-
way pipe
-r The given names are marked readonly and these names cannot be
changed by subsequent assignment.
-t Tags the named parameters. 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 parameters which have these flags
set is printed. (Using + rather than - keeps 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 Lists all of the current resource limits.
-d imposes a size limit of n kbytes on the size of the data area.
-f imposes a size limit of n 512 byte blocks on files written by
child processes (files of any size may be read).
-m imposes a soft limit of n kbytes on the size of physical
memory.
-p changes the pipe size to n (UNIX/RT only).
-s imposes a size limit of n kbytes on the size of the stack area.
-t imposes a time limit of n seconds to be used by each process.
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, i. e.,
their values and attributes are erased. Readonly variables cannot
be unset. If the flag, -f, is set, then the names refer to function
names.
ver [systype[command]]
With no arguments, return the current value of the SYSTYPE
environment variable that specifies the version of UNIX commands
being executed by the shell. With a systype argument, change the
SYSTYPE environment variable to either bsd4.3 or sys5.3, depending
on which is specified.
wait [ n ]
Wait for the specified child process and report its termination
status. If n is not given then all currently active child processes
are waited for. The return code from this command is that of the
process waited for.
whence [ -v ] name ...
For each name, indicate how it would be interpreted if used as a
command name.
The flag -v produces a more verbose report.
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 parameter 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
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 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.
-Dname=value
You can use the -D option to specify a parameter name that will
be set to value and then passed into the shell's environment.
This Domain/OS option is useful for tailoring the environment
of a shell invoked from a program that is not another shell
(such as the Display Manager). If the ENV parameter is given in
this way, the startup script it specifies will be run. Note
that any number of -D options can be specified.
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 ksh, 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 (i.e.,
/usr/rbin) that can be safely invoked by rksh Some systems also provide a
restricted editor red.
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. Runtime 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.
CAVEATS
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.
Scripts that invoke the ksh interpreter with "#!/bin/ksh" and have a
filename suffix of .rsh or .rksh are executed in rksh.
Some very old shell scripts contain a ^ as a synonym for the pipe
character |.
If a command is piped into a shell command, then 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
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.
FILES
/etc/passwd
/etc/profile
/etc/suid_profile
$HOME/.profile
/tmp/sh*
/dev/null
SEE ALSO
cat(1), cd(1), echo(1), test(1), vi(1), dup(2), exec(2), fork(2),
ioctl(2), lseek(2), pipe(2), umask(2), wait(2), rand(3), signal(3),
a.out(5), environ(7).