[LINUX] Variable parameter expansion of bash

Introduction

I will forget the variable parameter expansion of bash soon, so I will organize it.

Part of bash parameter expansion

There are many notations other than the above, but for the time being, there are four.

Example of use

$ {Variable name #Pattern}

$ {Variable name #Pattern} is a` parameter expansion that removes the part that matches the pattern with the shortest match.

.sh

#!/bin/bash

filepath=/home/name/abc.txt
echo "${filepath#*/}"

home/name/abc.txt

The shortest match is the ** shortest ** string that matches the specified pattern.

$ {Variable name ## pattern}

$ {Variable name #Pattern} is thelongest match, and is aparameter expansion that removes the prefix matching part of the pattern.

.sh

#!/bin/bash

filepath=/home/name/abc.txt
echo "${filepath##*/}"

abc.txt

The longest match refers to the ** longest ** string that matches the specified pattern.

It can be used to get the filename from the file path.

$ {Variable name% pattern}

$ {Variable name% pattern} is a parameter expansion that removes the trailing part of the pattern with the shortest match.

.sh

#!/bin/bash

filepath=/home/name/abc.txt
echo "${filepath%/*}"

/home/name

It can be used to get the directory of the file path without the filename.

$ {Variable name %% pattern}

$ {Variable name %% pattern} is a `parameter expansion that removes the part that is the longest match and the trailing part of the pattern.

.sh

#!/bin/bash

filepath=/home/name/abc.txt
echo "${filepath%%/*}"

(None)

reference

New Linux textbook