Functions
A shell function is a grouping of commands within a shell script. Shell functions let you modularize your program by dividing it up into separate tasks. This way, the code for each task need not be repeated every time you need to perform the task. The POSIX shell syntax for defining a function follows the Bourne shell:
name
() {function body's code come here
}
Functions are invoked just as are regular shell built-in commands
or external commands. The command-line parameters $1
, $2
, and
so on receive the function's arguments, temporarily hiding the global
values of $1
, etc. For
example:
# fatal --- print an error message and die: fatal () { echo "$0: fatal error:" "$@" >&2 # messages to standard error exit 1 } … if [ $# = 0 ] # not enough arguments then fatal not enough arguments fi
A function may use the return command to return an exit value to the calling shell program. Be careful not to use exit from within a function unless you really wish to terminate the entire program.
Bash allows you to define functions using an additional keyword, function, as follows:
function fatal { echo "$0: fatal error:" "$@" >&2 # messages to standard error exit 1 }
In Bash, all functions share traps with the "parent" shell (except
the DEBUG
trap, if function tracing
has been turned on). With the errtrace
option enabled (either set -E
or set -o
errtrace
), functions also inherit the ERR
trap. If function tracing has been
enabled, functions inherit the RETURN
trap. Functions may have local variables, ...
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