How to do it...

A function is defined with the function command, a function name, open/close parentheses, and a function body enclosed in curly brackets:

1. A function is defined as follows:

        function fname() 
        { 
            statements; 
        }  

Alternatively, it can be defined as:

        fname() 
        { 
            statements; 
        } 

It can even be defined as follows (for simple functions):

        fname() { statement; }

1. A function is invoked using its name:

        $ fname ; # executes function

1. Arguments passed to functions are accessed positionally, $1 is the first argument, $2 is the second, and so on:

        fname arg1 arg2 ; # passing args

The following is the definition of the function fname. In the fname function, we have included various ways of accessing the function arguments.

        fname() 
        { 
           echo $1, $2; #Accessing arg1 and arg2 
           echo "$@"; # Printing all arguments as list at once 
           echo "$*"; # Similar to $@, but arguments taken as single  
           entity 
           return 0; # Return value 
         }

Arguments passed to scripts can be accessed as $0 (the name of the script):

• • $1 is the first argument
  • $2 is the second argument
  • $n is the nth argument
  • "$@" expands as "$1" "$2" "$3" and so on
  • "$*" expands as "$1c$2c$3", where c is the first character of IFS
  • "$@" is used more often than $*, since the former provides all arguments as a single string
• Compare alias to function
• Here's an alias to display a subset of files by piping ls output to grep. The argument is attached to the end of the command, so lsg txt is expanded to ls | grep txt:

        $> alias lsg='ls | grep' 
        $> lsg txt 
          file1.txt 
          file2.txt 
          file3.txt 

• If we wanted to expand that to get the IP address for a device in /sbin/ifconfig, we might try the following:

        $> alias wontWork='/sbin/ifconfig | grep' 
        $> wontWork eth0 
        eth0  Link  encap:Ethernet  HWaddr 00:11::22::33::44:55 

• The grep command found the eth0 string, not the IP address. If we use a function instead of an alias, we can pass the argument to the ifconfig, instead of appending it to the grep:

        $> function getIP() { /sbin/ifconfig $1 | grep 'inet ';  } 
        $> getIP eth0 
        inet addr:192.168.1.2 Bcast:192.168.255.255 Mask:255.255.0.0