Using Functions in Shell Scripts
As with other programming languages, in Ubuntu shell programs also support
functions. A function is a piece of a shell program that performs a particular
process; you can reuse the same function multiple times within the shell
program. Functions help eliminate the need for duplicating code as you write
shell programs.
The following is the format of a function in pdksh and bash:
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func(){
Statements
}
You can call a function as follows:
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func param1 param2 param3
The parameters param1, param2, and so on are optional. You can also pass
the parameters as a single string—for example, $@. A function can parse the
parameters as if they were positional parameters passed to a shell program
from the command line as command-line arguments but instead use values
passed inside the script. For example, the following script uses a function
named Displaymonth() that displays the name of the month or an error
message if you pass a month number out of the range 1 to 12. This example
works with pdksh and bash:
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#!/bin/sh
Displaymonth() {
case $1 in
01 | 1) echo "Month is January";;
02 | 2) echo "Month is February";;
03 | 3) echo "Month is March";;
04 | 4) echo "Month is April";;
05 | 5) echo "Month is May";;
06 | 6) echo "Month is June";;
07 | 7) echo "Month is July";;
08 | 8) echo "Month is August";;
09 | 9) echo "Month is September";;
10) echo "Month is October";;
11) echo "Month is November";;
12) echo "Month is December";;
*) echo "Invalid parameter";;
esac
}