4.3BSD-Reno/share/man/cat1/case.0
SH(1) UNIX Reference Manual SH(1)
NNAAMMEE
sshh - shell command interpreter
SSYYNNOOPPSSIISS
sshh [--cceeiikknnrrssttuuvvxx] [arg] ...
DDEESSCCRRIIPPTTIIOONN
SShh is a command programming language that executes commands read from a
terminal or a file. The shell this page describes is called the _B_o_u_r_n_e
shell.
Command line options:
If the first character of argument 0 if commands are read from
$_H_O_M_E/._p_r_o_f_i_l_e, if such a file exists. The following flags are inter-
preted by the shell when it is invoked.
--cc _s_t_r_i_n_g
Commands are read from _s_t_r_i_n_g.
--ss If the --ss flag is present or if no arguments remain then com-
mands are read from the standard input. Shell output is writ-
ten to file descriptor 2.
--ii If the --ii flag is present or if the shell input and output are
attached to a terminal (as told by getty) then this shell is
_i_n_t_e_r_a_c_t_i_v_e. In this case the terminate signal SIGTERM (see
sigvec(2)) is ignored (so that 'kill 0' does not kill an in-
teractive shell) and the interrupt signal SIGINT is caught and
ignored (so that wait is interruptible). In all cases SIGQUIT
is ignored by the shell.
This next set of options can be used on the command line invoking the sshh
or set with the interactive command sseett.
--ee If non interactive, exit immediately if a command fails.
--kk All keyword arguments are placed in the environment for a com-
mand, not just those that precede the command name.
--nn Read commands but do not execute them.
--tt Exit after reading and executing one command.
--uu Treat unset variables as an error when substituting.
--vv Print shell input lines as they are read.
--xx Print commands and their arguments as they are executed.
-- Turn off the --xx and --vv options.
CCoommmmaannddss ..
A _s_i_m_p_l_e-_c_o_m_m_a_n_d is a sequence of non blank _w_o_r_d_s separated by blanks (a
blank is a _t_a_b or a _s_p_a_c_e). 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 execve(2)). The _v_a_l_u_e of a simple-command is
its exit status if it terminates normally or 200+_s_t_a_t_u_s if it terminates
abnormally (see _s_i_g_v_e_c _2 for a list of status values).
A _p_i_p_e_l_i_n_e is a sequence of one or more _c_o_m_m_a_n_d_s 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.
A _l_i_s_t is a sequence of one or more _p_i_p_e_l_i_n_e_s separated by ;;, &&, &&&& or ||
or |||| and optionally terminated by ;; or &&. ;; and && have equal precedence
which is lower than that of &&&& and ||||, &&&& and ||||, also have equal pre-
cedence. A semicolon causes sequential execution; an ampersand causes
the preceding _p_i_p_e_l_i_n_e to be executed without waiting for it to finish.
The symbol &&&& (||||) causes the _l_i_s_t following to be executed only if the
preceding _p_i_p_e_l_i_n_e returns a zero (non zero) value. Newlines may appear
in a _l_i_s_t, instead of semicolons, to delimit commands.
A _c_o_m_m_a_n_d is either a simple-command or one of the following. The value
returned by a command is that of the last simple-command executed in the
command.
ffoorr _n_a_m_e [iinn _w_o_r_d ...] ddoo _l_i_s_t ddoonnee
Each time a ffoorr command is executed _n_a_m_e is set to the next
word in the ffoorr word list. If iinn _w_o_r_d ... is omitted, iinn
``$$@@'' is assumed. Execution ends when there are no more words
in the list.
ccaassee _w_o_r_d iinn [_p_a_t_t_e_r_n [| _p_a_t_t_e_r_n ...] )) _l_i_s_t ;;;;] ..._e_s_a_c
A ccaassee command executes the _l_i_s_t associated with the first pat-
tern that matches _w_o_r_d. The form of the patterns is the same
as that used for file name generation.
iiff _l_i_s_t tthheenn _l_i_s_t [eelliiff _l_i_s_t tthheenn _l_i_s_t] ... [eellssee _l_i_s_t] ffii
The _l_i_s_t following iiff is executed and if it returns zero the
_l_i_s_t following tthheenn is executed. Otherwise, the _l_i_s_t following
eelliiff is executed and if its value is zero the _l_i_s_t following
tthheenn is executed. Failing that the eellssee _l_i_s_t is executed.
wwhhiillee _l_i_s_t [ddoo _l_i_s_t] ddoonnee
A wwhhiillee command repeatedly executes the wwhhiillee _l_i_s_t and if its
value is zero executes the ddoo _l_i_s_t; otherwise the loop ter-
minates. The value returned by a wwhhiillee command is that of the
last executed command in the ddoo _l_i_s_t. uunnttiill may be used in
place of wwhhiillee to negate the loop termination test.
(_l_i_s_t) Execute _l_i_s_t in a subshell.
{_l_i_s_t} _l_i_s_t is simply executed.
The following words are only recognized as the first word of a command
and when not quoted.
iiff tthheenn eellssee eelliiff ffii ccaassee iinn eessaacc ffoorr wwhhiillee uunnttiill ddoo ddoonnee {{ }}
CCoommmmaanndd ssuubbssttiittuuttiioonn
The standard output from a command enclosed in a pair of back quotes (````)
may be used as part or all of a word; trailing newlines are removed.
PPaarraammeetteerr ssuubbssttiittuuttiioonn ..
The character $$ is used to introduce substitutable parameters. Position-
al parameters may be assigned values by sseett. Variables may be set by
writing
_n_a_m_e=_v_a_l_u_e [_n_a_m_e=_v_a_l_u_e] ...
$$ {{_p_a_r_a_m_e_t_e_r}} A _p_a_r_a_m_e_t_e_r is a sequence of letters, digits or un-
derscores (a _n_a_m_e), a digit, or any of the characters
** @@ ## ?? -- $$ !! The value, if any, of the parameter is
substituted. The braces are required only when
_p_a_r_a_m_e_t_e_r is followed by a letter, digit, or under-
score that is not to be interpreted as part of its
name. If _p_a_r_a_m_e_t_e_r is a digit, it is a positional
parameter. If _p_a_r_a_m_e_t_e_r is ** or @@ then all the posi-
tional parameters, starting with $$11, are substituted
separated by spaces. $$00 is set from argument zero
when the shell is invoked.
$$ {{_p_a_r_a_m_e_t_e_r--_w_o_r_d}}
If _p_a_r_a_m_e_t_e_r is set, substitute its value; otherwise
substitute _w_o_r_d.
$$ {{_p_a_r_a_m_e_t_e_r==_w_o_r_d }}
If _p_a_r_a_m_e_t_e_r is not set, set it to _w_o_r_d; the value of
the parameter is then substituted. Positional param-
eters may not be assigned to in this way.
$$ {{_p_a_r_a_m_e_t_e_r??_w_o_r_d}}
If _p_a_r_a_m_e_t_e_r is set, substitute its value; otherwise,
print _w_o_r_d and exit from the shell. If _w_o_r_d is omit-
ted, a standard message is printed.
$$ {{_p_a_r_a_m_e_t_e_r++_w_o_r_d}}
If _p_a_r_a_m_e_t_e_r is set, substitute _w_o_r_d; otherwise sub-
stitute nothing.
In the above _w_o_r_d is not evaluated unless it is to be used as the substi-
tuted string. (So that, for example, echo ${d-'pwd'} will only execute
_p_w_d if _d is unset.)
The following _p_a_r_a_m_e_t_e_r_s are automatically set by the shell.
## The number of positional parameters in decimal.
-- Options supplied to the shell on invocation or by _s_e_t.
?? The value returned by the last executed command in decimal.
$$ The process number of this shell.
!! The process number of the last background command invoked.
The following _p_a_r_a_m_e_t_e_r_s are used but not set by the shell.
HOME The default argument (home directory) for the ccdd
command.
PATH The search path for commands (see _e_x_e_c_u_t_i_o_n).
MAIL If this variable is set to the name of a mail file,
the shell informs the user of the arrival of mail in
the specified file.
PS1 Primary prompt string, by default '$ '.
PS2 Secondary prompt string, by default '> '.
IFS Internal field separators, normally _s_p_a_c_e, _t_a_b, and
_n_e_w_l_i_n_e. IFS is ignored if sshh is running as root or
if the effective user id differs from the real user
id.
BBllaannkk iinntteerrpprreettaattiioonn ..
After parameter and command substitution, any results of substitution are
scanned for internal field separator characters (those found in $$IFS) and
split into distinct arguments where such characters are found. Explicit
null arguments ("" or '') are retained. Implicit null arguments (those
resulting from _p_a_r_a_m_e_t_e_r_s that have no values) are removed.
FFiillee nnaammee ggeenneerraattiioonn ..
Following substitution, each command word is scanned for the characters
**, ?? and [[. If one of these characters appears, 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 pat-
tern, the word is left unchanged. The character .. at the start of a
file name or immediately following a //, and the character //, must be
matched explicitly.
** Matches any string, including the null string.
?? Matches any single character.
[[......]] Matches any one of the characters enclosed. A pair of
characters separated by -- matches any character lexically
between the pair.
QQuuoottiinngg ..
The following characters have a special meaning to the shell and cause
termination of a word unless quoted.
;; && (( )) || << >> nneewwlliinnee ssppaaccee ttaabb
A character may be _q_u_o_t_e_d by preceding it with a `\\'. \\nneewwlliinnee is ig-
nored. All characters enclosed between a pair of quote marks (`'),
except a single quote, are quoted. Inside double quotes (``'') parameter
and command substitution occurs and \\ quotes the characters \\'' and $$.
``$*'' is equivalent to ``$$11 $$22 ......'' whereas
``$$@@'' is equivalent to ``$$11'' ``$$22'' ... .
PPrroommppttiinngg ..
When used interactively, the shell prompts with the value of PS1 before
reading a command. If at any time a newline is typed and further input
is needed to complete a command, the secondary prompt $$PS2 is issued.
IInnppuutt//OOuuttppuutt ..
Before a command is executed its input and output may be redirected using
a special notation interpreted by the shell. The following may appear
anywhere in a simple-command or may precede or follow a _c_o_m_m_a_n_d and are
not passed on to the invoked command. Substitution occurs before _w_o_r_d or
_d_i_g_i_t is used.
<< _w_o_r_d Use file _w_o_r_d as standard input (file descriptor 0).
>> _w_o_r_d Use file _w_o_r_d as standard output (file descriptor 1). If the
file does not exist, it is created; otherwise it is truncated
to zero length.
>>>> _w_o_r_d Use file _w_o_r_d as standard output. If the file exists, output
is appended (by seeking to the end); otherwise the file is
created.
<<<< _w_o_r_d The shell input is read up to a line the same as _w_o_r_d, or end
of file. The resulting document becomes the standard input.
If any character of _w_o_r_d is quoted, no interpretation is placed
upon the characters of the document; otherwise, parameter and
command substitution occurs, \\nneewwlliinnee is ignored, and \\ is used
to quote the characters $$ '' and the first character of _w_o_r_d.
<<&& _d_i_g_i_t
The standard input is duplicated from file descriptor _d_i_g_i_t;
see dup(2). Similarly for the standard output using >>.
<<&&-- The standard input is closed. Similarly for the standard out-
put using >>.
If one of the above is preceded by a digit, the file descriptor created
is that specified by the digit (instead of the default 0 or 1). For ex-
ample,
... 2>&1
creates file descriptor 2 to be a duplicate of file descriptor 1.
If a command is followed by && then the default standard input for the
command is the empty file (_d_e_v/_n_u_l_l). Otherwise, the environment for the
execution of a command contains the file descriptors of the invoking
shell as modified by input output specifications.
EEnnvviirroonnmmeenntt
The environment is a list of name-value pairs that is passed to an exe-
cuted program in the same way as a normal argument list; see execve(2)
and environ(7). The shell interacts with the environment in several
ways. On invocation, the shell scans the environment and creates a
_p_a_r_a_m_e_t_e_r for each name found, giving it the corresponding value. Exe-
cuted commands inherit the same environment. If the user modifies the
values of these _p_a_r_a_m_e_t_e_r_s or creates new ones, none of these affects the
environment unless the eexxppoorrtt command is used to bind the shell's
_p_a_r_a_m_e_t_e_r to the environment. The environment seen by any executed com-
mand is thus composed of any unmodified name-value pairs originally in-
herited by the shell, plus any modifications or additions, all of which
must be noted in eexxppoorrtt commands.
The environment for any _s_i_m_p_l_e-_c_o_m_m_a_n_d may be augmented by prefixing it
with one or more assignments to _p_a_r_a_m_e_t_e_r_s. Thus these two lines are
equivalent
TERM=450 cmd args
(export TERM; TERM=450; cmd args)
If the --kk flag is set, _a_l_l keyword arguments are placed in the environ-
ment, even if they occur after the command name. The following prints
'a=b c' and 'c':
echo a=b c
set -k
echo a=b c
SSiiggnnaallss ..
The INTERRUPT and QUIT signals for an invoked command are ignored if the
command is followed by &&; otherwise signals have the values inherited by
the shell from its parent. (But see also ttrraapp.)
EExxeeccuuttiioonn ..
Each time a command is executed the above substitutions are carried out.
Except for the 'special commands' listed below a new process is created
and an attempt is made to execute the command via an execve(2).
The shell parameter $$$PATH defines the search path for the directory
containing the command. Each alternative directory name is separated by
a colon (::). The default path is :/_b_i_n:/_u_s_r/_b_i_n. If the command name
contains a //, the search path is not used. Otherwise, each directory in
the path is searched for an executable file. If the file has execute
permission but is not an _a._o_u_t file, it is assumed to be a file contain-
ing shell commands. A subshell (i.e., a separate process) is spawned to
read it. A parenthesized command is also executed in a subshell.
SSppeecciiaall ccoommmmaannddss ..
The following commands are executed in the shell process and except where
specified no input output redirection is permitted for such commands.
## For non-interactive shells, everything following the ## is
treated as a comment, i.e. the rest of the line is ignored.
For interactive shells, the ## has no special effect.
:: No effect; the command does nothing.
.._f_i_l_e Read and execute commands from _f_i_l_e and return. The search
path $$PATH is used to find the directory containing _f_i_l_e.
bbrreeaakk [_n]
Exit from the enclosing ffoorr or wwhhiillee loop, if any. If _n is
specified, break _n levels.
ccoonnttiinnuuee [_n]
Resume the next iteration of the enclosing ffoorr or wwhhiillee loop.
If _n is specified, resume at the _n'th enclosing loop.
ccdd [_a_r_g]
Change the current directory to _a_r_g. The shell parameter
$$$HOME is the default _a_r_g.
eevvaall [_a_r_g ...]
The arguments are read as input to the shell and the resulting
command(s) executed.
eexxeecc [_a_r_g ...]
The command specified by the arguments is executed in place of
this shell without creating a new process. Input output
arguments may appear and if no other arguments are given cause
the shell input output to be modified.
eexxiitt [_n]
Causes a non interactive shell to exit with the exit status
specified by _n. If _n is omitted, the exit status is that of
the last command executed. (An end of file will also exit from
the shell.)
eexxppoorrtt [_n_a_m_e ...]
The given names are marked for automatic export to the
_e_n_v_i_r_o_n_m_e_n_t of subsequently-executed commands. If no arguments
are given, a list of exportable names is printed.
llooggiinn [_a_r_g ...]
Equivalent to 'exec login arg ...'.
rreeaadd _n_a_m_e ...
One line is read from the standard input; successive words of
the input are assigned to the variables _n_a_m_e in order, with
leftover words to the last variable. The return code is 0 un-
less the end-of-file is encountered.
rreeaaddoonnllyy [_n_a_m_e ...]
The given names are marked readonly and the values of the these
names may not be changed by subsequent assignment. If no
arguments are given, a list of all readonly names is printed.
sseett [--eekknnppttuuvvxx] [_a_r_g ...]
The set flags are described in the options section at the
beginning of this man page. The current set of flags may be
found in $$--.
Remaining arguments after the flag are positional parameters
and are assigned, in order, to $$11, $$22, etc. If no arguments
are given, the values of all names are printed.
sshhiifftt The positional parameters from $$22 ...... are renamed $$11 ......
ttiimmeess Print the accumulated user and system times for processes run
from the shell.
ttrraapp [_a_r_g] [_n] ...
_A_r_g is a command to be read and executed when the shell re-
ceives signal(s) _n. (Note that _a_r_g is scanned once when the
trap is set and once when the trap is taken.) Trap commands are
executed in order of signal number. If _a_r_g is absent, all
trap(s) _n are reset to their original values. If _a_r_g is the
null string, this signal is ignored by the shell and by invoked
commands. If _n is 0, the command _a_r_g is executed on exit from
the shell, otherwise upon receipt of signal _n as numbered in
sigvec(2). TTrraapp with no arguments prints a list of commands
associated with each signal number.
uummaasskk [_n_n_n]
The user file creation mask is set to the octal value _n_n_n (see
umask(2)). If _n_n_n is omitted, the current value of the mask is
printed.
wwaaiitt [_n]
Wait for the specified process and report its termination
status. If _n is not given, all currently active child
processes are waited for. The return code from this command is
that of the process waited for.
FFIILLEESS
$_H_O_M_E/._p_r_o_f_i_l_e
/_t_m_p/_s_h*
/_d_e_v/_n_u_l_l
SSEEEE AALLSSOO
csh(1), test(1), execve(2), environ(7)
DDIIAAGGNNOOSSTTIICCSS
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
eexxiitt).
HHIISSTTOORRYY
The SShh shell appeared in Version 6 AT&Y UNIX. If <<<< is used to provide
standard input to an asynchronous process invoked by &&, the shell gets
mixed up about naming the input document. A garbage file /_t_m_p/_s_h* is
created, and the shell complains about not being able to find the file by
another name.