term% cat index.txt SH(1) General Commands Manual SH(1)
NAME
ksh - Korn shell, the not standard command programming language
SYNOPSIS
ksh [ -acefhikmnorstuvx ] [ -o option ] ... [ arg ... ]
DESCRIPTION
Ksh is a command programming language that executes commands read from
a terminal or a file. Rsh is a restricted version of the standard com‐
mand interpreter sh; it is used to set up login names and execution en‐
vironments 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. Identi‐
fiers 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 in‐
voked 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 nor‐
mally, 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 out‐
put of the spawned command can be written to and read from by the par‐
ent 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 ar‐
bitrary number of new-lines may appear in a list, instead of semi‐
colons, 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 omit‐
ted, then the for command executes the do list once for each po‐
sitional parameter that is set (see Parameter Substitution be‐
low). 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 pa‐
rameter identifier is set to the word corresponding to this num‐
ber. 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 pat‐
tern that matches word. The form of the patterns is the same as
that used for file-name generation (see File Name Generation be‐
low).
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. Other‐
wise, 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 adja‐
cent open parentheses are needed for nesting, a space must be
inserted to avoid arithmetic evaluation 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 com‐
mand and when not quoted:
if then else elif fi case esac for while until do done { } function se‐
lect time
Comments.
A word beginning with # causes that word and all the following charac‐
ters 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 rest of the charac‐
ters 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 spe‐
cial 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 exe‐
cuted. 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 au‐
tomatically 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 identifier is read 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 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, 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 lo‐
gin directory of the matched user. This is called a tilde substitu‐
tion. 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 pa‐
rameter. A ∼ followed by a + or - is replaced by the value of the pa‐
rameter 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 a pair of grave accents
(``) may be used as part or all of a word; trailing new-lines are re‐
moved. 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, a digit, or any of the characters ∗, @,
#, ?, -, $, and !. A named parameter (a parameter denoted by an iden‐
tifier) 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 at‐
tributes to sub-shells but only values to the environment.
The shell supports a limited one-dimensional array facility. An ele‐
ment 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 ref‐
erence to a named parameter with a valid subscript is legal and an ar‐
ray will be created if necessary. Referencing an array without a sub‐
script 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 a digit
then it is a positional parameter. If parameter is ∗ or @, then
all the positional parameters, starting with $1, are substituted
(separated by spaces). If an array identifier with subscript ∗
or @ is used, then the value for each of the elements is substi‐
tuted (separated by spaces).
${#parameter}
If parameter is not ∗, the length of the value of the parameter
is substituted. Otherwise, the number of positional parameters
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 parame‐
ters 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 omit‐
ted then a standard message is printed.
${parameter:+word}
If parameter is set and is non-null then substitute word; other‐
wise substitute nothing.
${parameter#pattern}
${parameter##pattern}
If the Shell pattern matches the beginning of the value of pa‐
rameter, 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 small‐
est 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; oth‐
erwise 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 sub‐
stituted 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 parame‐
ter is not set for commands which are asynchronous.
! The process number of the last background command in‐
voked.
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 ini‐
tialized 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.
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 correspond‐
ing option (see Special Command set below) will be turned
on.
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.
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.
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 be‐
low.)
HISTSIZE
If this parameter is set when the shell is invoked, then
the number of previously entered commands that are acces‐
sible 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.
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. If set to 0, the shell
will check before each prompt.
MAILPATH
A colon ( : ) separated list of file names. If this pa‐
rameter 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 $_.
PATH The search path for commands (see Execution below). The
user may not change PATH if executing under rsh (except
in .profile ).
PS1 The value of this parameter is expanded for paramter sub‐
stitution to define the primary prompt string which by
default is ``$ ''. The character ! in the primary
prompt string is replaced by the command number (see Com‐
mand Re-entry below).
PS2 Secondary prompt string, by default ``> ''.
PS3 Selection prompt string used within a select loop, by de‐
fault ``#? ''.
SHELL The pathname of the shell is kept in the environment. At
invocation, if the value of this variable contains an r
in the basename, then the shell becomes restricted.
TMOUT If set to a value greater than zero, the shell will ter‐
minate if a command is not entered within the prescribed
number of seconds. (Note that the shell can be compiled
with a maximum bound for this value which cannot be ex‐
ceeded.)
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. Ex‐
plicit null arguments ("" or (fm(fm) are retained. Implicit null argu‐
ments (those resulting from parameters that have no values) are re‐
moved.
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 charac‐
ters appears then the word is regarded as a pattern. The word is re‐
placed 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 spe‐
cially.
∗ 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 fol‐
lowing the opening "[ " is a "! " then any character not
enclosed is matched. A - can be included in the charac‐
ter 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 cause 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 (′′), except a single
quote, are quoted. Inside double quote marks (""), parameter and com‐
mand substitution occurs and \ quotes the characters \, ′, ", and $.
"$∗" is equivalent to "$1 $2 ...", whereas "$@" is equivalent to "$1"
"$2" ....
The special meaning of keywords can be removed by quoting any character
of the keyword. The recognition of 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. Con‐
stants 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 speci‐
fied with the -i option of the typeset special command. When this at‐
tribute 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 in‐
put 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 (by first seeking to the
end-of-file); 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 charac‐
ters of the document; otherwise, parameter and command
substitution occurs, \new-line is ignored, and \ must be
used to quote the characters \, $, `, and the first char‐
acter 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 de‐
fault 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 ex‐
port . Executed commands inherit the environment. If the user modi‐
fies the values of these parameters or creates new ones, using the ex‐
port 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 mod‐
ified 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 as‐
signment 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 fol‐
lowing 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 in‐
ternally. Alias names are resolved when the function is read. Func‐
tions are executed like commands with the arguments passed as posi‐
tional 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 af‐
ter 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 in‐
cludes the current function and all functions it calls.
The special command return is used to return from function calls. Er‐
rors 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 num‐
bers. 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 ver‐
sions of UNIX and may not apply. If you are running a job and wish to
do something else you may hit the key ^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 ma‐
nipulate 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 out‐
put 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 out‐
put pertaining to jobs, the current job is marked with a + and the pre‐
vious 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 com‐
mand 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.
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 com‐
mand name is checked to see if it matches one of the user defined func‐
tions. 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 com‐
mand 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 con‐
taining the command. Alternative directory names are separated by a
colon (:). The default path is :/bin:/usr/bin (specifying the current
directory, /bin, and /usr/bin, in that order). Note that the current
directory is specified by a null path name, which can appear immedi‐
ately after the equal sign, between colon delimiters, or at the 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 di‐
rectory 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. A
parenthesized command is also executed in a sub-shell.
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/.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 por‐
tion 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 pa‐
rameter 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 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 op‐
tion. 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 over‐
write 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.
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 exam‐
ple, ^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 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.
^K Kill from the cursor to the end of the line. If given a pa‐
rameter of zero then kill from the start of line to the cur‐
sor.
^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 ter‐
minals).
^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 for‐
ward. String is terminated by a "RETURN" or "NEW LINE".
^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 and ^N.
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 line. The letter must not be
one of the above meta-functions.
M-_ The last parameter of the previous command is inserted on the
line.
M-. The last parameter of the previous command is inserted on the
line.
M-* Attempt file name generation on the current word.
^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 en‐
abled 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 canon‐
ical processing with the type-ahead echoing of raw mode.
If the option viraw is also set, the terminal will always have canoni‐
cal 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 $a.
[count]cmotion
c[count]motion
Delete current character through the character motion
moves the cursor to and enter input mode. If motion
is c, the entire line will be deleted and input mode
entered.
C Delete the current character through the end of line
and enter input mode. Equivalent to c$.
S Equivalent to cc.
D Delete the current character through the end of line.
[count]dmotion
d[count]motion
Delete current character through the character motion
moves the cursor to. 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. Equiva‐
lent to the two character sequence ^i.
[count]P Place the previous text modification before the cur‐
sor.
[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
Miscellaneous commands.
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.
Equivalent to
I#<cr>. Useful for causing the current line to be in‐
serted in the history without being executed.
Special Commands.
The following simple-commands are executed in the shell process. In‐
put/Output redirection is permitted. File descriptor 1 is the default
output location. Parameter assignment lists preceding the command do
not remain in effect when the command completes unless noted.
: [ arg ... ]
Parameter assignments remain in effect after the command com‐
pletes. The command only expands parameters. A zero exit code
is returned.
. file [ arg ... ]
Parameter assignments remain in effect after the command com‐
pletes. 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 con‐
taining 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 con‐
trol. 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 enclos‐
ing 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 direc‐
tory is changed to the previous directory. The shell parameter
HOME is the default arg. The parameter PWD is set to the cur‐
rent 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 di‐
rectory is specified by a null path name, which can appear imme‐
diately 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 direc‐
tory.
The cd command may not be executed by rsh.
eval [ arg ... ]
The arguments are read as input to the shell and the resulting
command(s) executed.
exec [ arg ... ]
Parameter assignments remain in effect after the command com‐
pletes. 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 cur‐
rent process. If no arguments are given the effect of this com‐
mand is to modify file descriptors as prescribed by the in‐
put/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 ex‐
cept 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 environ‐
ment 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 se‐
lected 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 re‐
cent 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 con‐
taining 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. 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 con‐
trol. If job is specified it brings it to the foreground. Oth‐
erwise, the current job is brought into the foreground.
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 names are listed by kill
-l'. There is no default, saying just `kill' does not send a
signal to the current job. 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 cal‐
culations 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 = opera‐
tor 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 lev‐
els 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 ⎪& in‐
stead 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 out‐
put.
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 contin‐
uation. The first word is assigned to the first name, the sec‐
ond 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 us‐
ing ⎪&. If the -s fag 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 de‐
scriptor can be opened with the exec special command. The de‐
fault 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 de‐
scriptor 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 re‐
turn status is that of the last command executed. If return is
invoked while not in a function then it is the same as an exit.
set [ -aefhkmnostuvx ] [ -o option ... ] [ arg ... ]
The flags for this command have meaning as follows:
-a All subsequent parameters that are defined are automati‐
cally 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 en‐
vironment 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 auto‐
matically for interactive shells.
-n Read commands but do not execute them.
-o The following argument can be one of the following op‐
tion names:
allexport
Same as -a.
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.
verbose Same as -v.
trackall
Same as -h.
vi Puts you in insert mode of a vi style in-line
editor until you hit escape character 033. This
puts you in move mode. A return sends the line.
viraw Each character is processed as it is typed in vi
mode.
xtrace Same as -x.
If no option name is supplied then the current option
settings are printed.
-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 argu‐
ments 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 expres‐
sion 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 re‐
stricted 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 exe‐
cuted in order of signal number. Any attempt to set a trap on a
signal that was ignored on entry to the current shell is inef‐
fective. An attempt to trap on signal 11 (memory fault) pro‐
duces an error. 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 exe‐
cuted inside the body of a function, then the command arg is ex‐
ecuted 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 [ -FLRZefilprtux[n ] [ name[ =value ] ] ... ]
Parameter assignments remain in effect after the command com‐
pletes. When invoked inside a function, a new instance of the
parameter name is created. The parameter value and type are re‐
stored when the function completes. The following list of at‐
tributes may be specified:
-F 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 as‐
signment. When the parameter is assigned to, it is
filled on the right with blanks or truncated, if neces‐
sary, 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 cur‐
rently unused by the shell and can be set or cleared by
the user.
-f The names refer to function names rather than parameter
names. No assignments can be made and the only other
valid flag is -x.
-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 can‐
not 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 [ -cdfmpt ] [ n ]
-c imposes a size limit of n blocks on the size of core
dumps (BSD only).
-d imposes a size limit of n blocks on the size of the data
area (BSD only).
-f imposes a size limit of n blocks on files written by
child processes (files of any size may be read).
-m imposes a soft limit of n blocks on the size of physical
memory (BSD only).
-p changes the pipe size to n (UNIX/RT only).
-t imposes 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, i. e.,
their values and attributes are erased. Readonly variables can‐
not be unset. If the flag, -f, is set, then the names refer to
function names.
wait [ n ]
Wait for the specified process and report its termination sta‐
tus. If n is not given then all currently active child pro‐
cesses 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 com‐
mands are read from /etc/profile and then from either .profile in the
current directory or $HOME/.profile, if either file exists. Next, com‐
mands are read from the file named by performing parameter substitution
on the value of the environment parameter ENV if the file exists. Com‐
mands are then read as described below; the following flags are inter‐
preted 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 com‐
mands 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 told by gtty(2)) then this
shell is interactive. In this case TERMINATE is ignored (so
that kill 0 does not kill an interactive shell) and INTERRUPT
is caught and ignored (so that wait is interruptible). In
all cases, QUIT is ignored by the shell.
-r If the -r flag is present the shell is a restricted shell.
The remaining flags and arguments are described under the set command
above.
Rsh Only.
Rsh is used to set up login names and execution environments whose ca‐
pabilities are more controlled than those of the standard shell. The
actions of rsh are identical to those of sh, except that the following
are disallowed:
changing directory (see cd(1)),
setting the value of SHELL 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, rsh in‐
vokes sh to execute it. Thus, it is possible to provide to the end-
user shell procedures that have access to the full power of the stan‐
dard shell, while imposing a limited menu of commands; this scheme as‐
sumes 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 ac‐
tions 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 rsh. Some systems also pro‐
vide 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. If the shell is being used non-interac‐
tively then execution of the shell file is abandoned. Otherwise, the
shell returns the exit status of the last command executed (see also
the exit command above).
FILES
/etc/passwd
/etc/profile
$HOME/.profile
/tmp/sh∗
/dev/null
SEE ALSO
cat(1), cd(1), echo(1), emacs(1), env(1), gmacs(1), newgrp(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(3), a.out(5), profile(5), envi‐
ron(7).
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 be‐
fore 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
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 ^ as a synonym for the pipe char‐
acter ⎪.
SH(1)