How to Use Command Line Arguments in Bash Scripts

In Bash, command line arguments are accessed using special variables like $1, $2, etc., where $1 is the first argument. The total number of arguments is stored in $#, and all arguments together are in $@.

Syntax

In a Bash script, command line arguments are accessed using positional parameters:

• $0: The script name.
• $1, $2, ...: The first, second, and subsequent arguments.
• $#: Number of arguments passed.
• $@: All arguments as separate words.
• $*: All arguments as a single string.

bash

script.sh arg1 arg2 arg3

# Inside script.sh
# $0 = script.sh
# $1 = arg1
# $2 = arg2
# $3 = arg3
# $# = 3
# $@ = arg1 arg2 arg3
# $* = arg1 arg2 arg3

Example

This example script prints each command line argument with its position and shows the total count.

bash

#!/bin/bash

echo "Script name: $0"
echo "Number of arguments: $#"

count=1
for arg in "$@"
do
  echo "Argument $count: $arg"
  ((count++))
done

Output

Script name: ./example.sh
Number of arguments: 3
Argument 1: apple
Argument 2: banana
Argument 3: cherry

Common Pitfalls

Common mistakes include:

• Not quoting $@ which can cause arguments with spaces to split incorrectly.
• Using $* without quotes, which concatenates all arguments into one string.
• Accessing arguments beyond $# which are empty.

Always quote variables like "$@" to preserve argument boundaries.

bash

# Wrong way (arguments with spaces break):
for arg in $@
do
  echo "$arg"
done

# Right way:
for arg in "$@"
do
  echo "$arg"
done

Quick Reference

Variable	Meaning
$0	Script name
$1, $2, ...	First, second, etc. arguments
$#	Number of arguments
$@	All arguments as separate words
$*	All arguments as a single string

Key Takeaways

Use $1, $2, etc., to access individual command line arguments in Bash.

Always quote "$@" when looping over arguments to handle spaces correctly.

Use $# to check how many arguments were passed to your script.

Avoid using $* without quotes as it merges all arguments into one string.

Remember $0 holds the script's name, not an argument.