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variable replacement and truncate in bash

Delete

Left -> Right

1. 一次性从前向后匹配删除

VAR=hahaha
echo ${VAR#*h}
# ahaha

2. 贪婪模式，从前向后匹配删除

VAR=hahaha
echo ${VAR##*h}
# a

Right -> Left

1. 一次性从后向前匹配删除

VAR=hahaha
echo ${VAR%a*}
# hahah

2. 贪婪模式，从后向前匹配删除

VAR=hahaha
echo ${VAR%%a*}
# h

About % and #

  • # 是去掉左边 (在键盘上 # 在 % 的左边)
  • % 是去掉右边 (在键盘上 % 在 # 的右边)
  • 符号用一次是最小匹配，两个连用就是最大匹配

Replacement

一次性替换

VAR=hahaha
echo ${VAR/a/A}
# hAhaha

贪婪模式，全部替换

VAR=hahaha
echo ${VAR//a/A}
# hAhAhA

Truncate

VAR=hahaha
echo ${VAR:0:5} #提取起始 1-5 个字节
# hahah
echo ${VAR:3:2} #提取第 3 个字节右边的连续 2 个字节
# ah

Disclaimer
  1. License under CC BY-NC 4.0
  2. Copyright issue feedback me#imzye.me, replace # with @
  3. Not all the commands and scripts are tested in production environment, use at your own risk
  4. No privacy information is collected here
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