Working with command-line arguments (special variables, set and shift, getopt)

Command-line arguments are required for the following reasons:

• They inform the utility, or they command which file or group of files to process (reading/writing of files)
• Command-line arguments tell the command/utility which option to use

Check out the following command line:

[student@localhost ~]$  my_program  arg1  arg2  arg3

If my_command is a bash shell script, then we can access every command-line positional parameter inside the script, as follows:

$0 would contain "my_program"          # Command 
$1 would contain "arg1"                # First parameter 
$2 would contain "arg2"                # Second parameter 
$3 would contain "arg3"                # Third parameter 

The following is a summary of the positional parameters:

Let's create a script parameter.sh, as follows:

#!/bin/bash 
echo "Total number of parameters are = $#" 
echo "Script name = $0" 
echo "First Parameter is $1" 
echo "Second Parameter is $2" 
echo "Third Parameter is $3" 
echo "Fourth Parameter is $4" 
echo "Fifth Parameter is $5" 
echo "All parameters are = $*" 

Then, as usual, give execute permission to the script and then execute it:

./parameter.sh London Washington Delhi Dhaka Paris

The output is as follows:

Total number of parameters are = 5Command is = ./parameter.shFirst Parameter is LondonSecond Parameter is WashingtonThird Parameter is DelhiFourth Parameter is DhakaFifth Parameter is ParisAll parameters are = London Washington Delhi Dhaka Paris