Linux in a Nutshell, Fifth Edition

Functions | 633

Bash and Korn

This is the Title of the Book, eMatter Edition

Copyright © 2006 O’Reilly & Associates, Inc. All rights reserved.

Examples

$ ed - memo |& Start coprocess

$ print -p /word/ Send ed command to coprocess

$ read -p search Read output of ed command into variable search

$ print "$search" Show the line on standard output

A word to the wise.

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 func-

tion’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 and the Korn shell allow you to define functions using ...