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Compound Commands

A compound command\fP is one of the following:

(list\fP)

list\fP is executed in a subshell. Variable assignments and builtin commands that affect the shell's environment do not remain in effect after the command completes. The return status is the exit status of list\fP.

{ list\fP; }

list\fP is simply executed in the current shell environment. list\fP must be terminated with a newline or semicolon. This is known as a group command\fP. The return status is the exit status of list\fP.

((expression\fP))

The expression\fP is evaluated according to the rules described below under .SM .BR "ARITHMETIC EVALUATION" . If the value of the expression is non-zero, the return status is 0; otherwise the return status is 1. This is exactly equivalent to let "expression\fP".

[[\fP expression\fP ]]\fP

Return a status of 0 or 1 depending on the evaluation of the conditional expression expression\fP. Expressions are composed of the primaries described below under .SM .BR "CONDITIONAL EXPRESSIONS" . Word splitting and pathname expansion are not performed on the words between the [[\fP and ]]\fP; tilde expansion, parameter and variable expansion, arithmetic expansion, command substitution, process substitution, and quote removal are performed. .if t .sp 0.5 .if n .sp 1 When the ==\fP and !=\fP operators are used, the string to the right of the operator is considered a pattern and matched according to the rules described below under Pattern Matching\fP. The return value is 0 if the string matches or does not match the pattern, respectively, and 1 otherwise. Any part of the pattern may be quoted to force it to be matched as a string. .if t .sp 0.5 .if n .sp 1 Expressions may be combined using the following operators, listed in decreasing order of precedence: .if t .sp 0.5 .if n .sp 1

( expression\fP )

Returns the value of expression\fP. This may be used to override the normal precedence of operators.

! expression\fP

True if expression is false.

expression1\fP &&\fP expression2\fP

True if both expression1 and expression2 are true.

.if t expression1\fP \(bv\(bv\fP expression2\fP

.if n expression1\fP ||\fP expression2\fP True if either expression1 or expression2 is true. .LP The &&\fP and .if t \(bv\(bv\fP .if n ||\fP operators do not execute expression2\fP if the value of expression1\fP is sufficient to determine the return value of the entire conditional expression.

for\fP name\fP [ in\fP word\fP ] ; do\fP list\fP ; done\fP

The list of words following in\fP is expanded, generating a list of items. The variable name\fP is set to each element of this list in turn, and list\fP is executed each time. If the in\fP word\fP is omitted, the for\fP command executes list\fP once for each positional parameter that is set (see .SM PARAMETERS below). The return status is the exit status of the last command that executes. If the expansion of the items following in\fP results in an empty list, no commands are executed, and the return status is 0.

for\fP (( expr1\fP ; expr2\fP ; expr3\fP )) ; do\fP list\fP ; done\fP

First, the arithmetic expression expr1\fP is evaluated according to the rules described below under .SM .BR "ARITHMETIC EVALUATION" . The arithmetic expression expr2\fP is then evaluated repeatedly until it evaluates to zero. Each time expr2\fP evaluates to a non-zero value, list\fP is executed and the arithmetic expression expr3\fP is evaluated. If any expression is omitted, it behaves as if it evaluates to 1. The return value is the exit status of the last command in list\fP that is executed, or false if any of the expressions is invalid.

select\fP name\fP [ in\fP word\fP ] ; do\fP list\fP ; done\fP

The list of words following in\fP is expanded, generating a list of items. The set of expanded words is printed on the standard error, each preceded by a number. If the in\fP word\fP is omitted, the positional parameters are printed (see .SM PARAMETERS below). The PS3 prompt is then displayed and a line read from the standard input. If the line consists of a number corresponding to one of the displayed words, then the value of name is set to that word. If the line is empty, the words and prompt are displayed again. If EOF is read, the command completes. Any other value read causes name to be set to null. The line read is saved in the variable .BR REPLY . The list is executed after each selection until a break or return command is executed. The exit status of select is the exit status of the last command executed in .IR list , or zero if no commands were executed.

case\fP word\fP in\fP [ [(] pattern\fP [ |\fP pattern\fP ] \

A case\fP command first expands word\fP, and tries to match it against each pattern\fP in turn, using the same matching rules as for pathname expansion (see Pathname Expansion below). When a match is found, the corresponding list\fP is executed. After the first match, no subsequent matches are attempted. The exit status is zero if no pattern matches. Otherwise, it is the exit status of the last command executed in list\fP.

if\fP list\fP; then\fP list;\fP \

[ elif\fP list\fP; then\fP list\fP; ] ... \ [ else\fP list\fP; ] fi\fP The if list is executed. If its exit status is zero, the then\fP list\fP is executed. Otherwise, each elif\fP list\fP is executed in turn, and if its exit status is zero, the corresponding then\fP list\fP is executed and the command completes. Otherwise, the else\fP list\fP is executed, if present. The exit status is the exit status of the last command executed, or zero if no condition tested true.

while\fP list\fP; do\fP list\fP; done\fP

until\fP list\fP; do\fP list\fP; done\fP

The while\fP command continuously executes the do\fP list\fP as long as the last command in list\fP returns an exit status of zero. The until\fP command is identical to the while\fP command, except that the test is negated; the do list is executed as long as the last command in list returns a non-zero exit status. The exit status of the while\fP and until\fP commands is the exit status of the last do\fP list\fP command executed, or zero if none was executed.

[ function\fP ] name\fP () { list\fP; }

This defines a function named name\fP. The body\fP of the function is the list of commands between { and }. This list is executed whenever name\fP is specified as the name of a simple command. The exit status of a function is the exit status of the last command executed in the body. (See .SM FUNCTIONS below.)

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