shift – Shift Position Parameter

The shift command is a built-in shell command in Linux that is used to shift the positional parameters of the command line arguments. It is used to move the positional parameters to the left or right by a certain number of positions. This command is mostly used in shell scripts where a function takes a variable number of arguments.

Overview

The shift command is used to shift the positional parameters of the command line arguments. It is often used in shell scripts to manipulate the command line arguments. The syntax of the shift command is as follows:

shift [n]

where n is an optional parameter that specifies the number of positions to shift. If n is not specified, it defaults to 1.

Examples

Suppose you have a script that takes three command line arguments, and you want to shift the positional parameters to the left by one position. You can do this using the shift command as follows:

#!/bin/bash

echo "The first argument is: $1"
echo "The second argument is: $2"
echo "The third argument is: $3"

shift

echo "The first argument is now: $1"
echo "The second argument is now: $2"

In this example, the shift command is used to shift the positional parameters to the left by one position. The first argument is discarded, and the second and third arguments are moved to the first and second positions, respectively.

Specific use cases

The shift command is often used in shell scripts that take a variable number of arguments. For example, suppose you have a script that takes a variable number of arguments, and you want to process each argument in turn. You can use a loop and the shift command to do this as follows:

#!/bin/bash

while [ $# -gt 0 ]
do
    echo "The argument is: $1"
    shift
done

In this example, the while loop is used to process each argument in turn. The shift command is used to shift the positional parameters to the left by one position after each iteration of the loop.

Options

The shift command has only one option:

Troubleshooting tips

If you get an error message such as “shift: can’t shift that many” when using the shift command, it means that you are trying to shift more positions than there are positional parameters. To avoid this error, you should always check the number of positional parameters before using the shift command.

Notes

• The shift command only affects the positional parameters of the current shell or shell script. It does not affect the environment variables or the positional parameters of any child processes.
• The shift command is a shell built-in command and is available in most Linux shells, including bash, zsh, and ksh.