shell 的 ${ }中 ##、%%、// 使用方法及举例

使用说明

#与##

${var#Pattern} Remove from $var the shortest part of $Pattern that matches the front end of $var.
${var##Pattern} Remove from $var the longest part of $Pattern that matches the front end of $var.

%与%%

${var%Pattern} Remove from $var the shortest part of $Pattern that matches the back end of $var.
${var%%Pattern} Remove from $var the longest part of $Pattern that matches the back end of $var.

简言之：
#是将${var}中的左边（键盘上 # 在 $ 的左边）的${Pattern}去掉；
%是将${var}中的右边（键盘上 % 在 $ 的右边）的${Pattern}去掉；
其中单一符号#或%是最小匹配；两个符号##或%%则是最大匹配。

/与//

${string/substring/replacement} Replace first match of $substring with $replacement.
${string//substring/replacement} Replace all matches of $substring with $replacement.

示例1

#!/bin/sh

str="This is This is my test string search_string"   #被测试字符串
subStr1="This is "                                   #待删除的字符串1
subStr2="string"                                     #待删除的字符串2

echo -e "Test 1 ${str#$subStr1}"
echo -e "Test 2 ${str##$subStr1}"
echo -e "Test 3 ${str#$subStr2}"
echo -e "Test 4 ${str##$subStr2}"
echo -e "Test 5 ${str#*$subStr1}"
echo -e "Test 6 ${str##*$subStr1}"
echo -e "Test 7 ${str##*$subStr1*}"
echo -e "Test 8 ${str##*$subStr2}"
echo -e "Test 9 ${str##*$subStr2*}"
echo -e
echo -e "Test 10 ${str%$subStr1}"
echo -e "Test 11 ${str%%$subStr1}"
echo -e "Test 12 ${str%$subStr2}"
echo -e "Test 13 ${str%%$subStr2}"
echo -e "Test 14 ${str%*$subStr1}"
echo -e "Test 15 ${str%%$subStr1*}"
echo -e "Test 16 ${str%*$subStr1*}"
echo -e "Test 17 ${str%$subStr2*}"
echo -e "Test 18 ${str%*$subStr2}"
echo -e "Test 19 ${str%%*$subStr2}"
echo -e "Test 20 ${str%%$subStr2*}"
echo -e "Test 21 ${str%%*$subStr2*}"
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其输出为：

Test 1 This is my test string search_string
Test 2 This is my test string search_string
Test 3 This is This is my test string search_string
Test 4 This is This is my test string search_string
Test 5 This is my test string search_string
Test 6 my test string search_string
Test 7
Test 8
Test 9

Test 10 This is This is my test string search_string
Test 11 This is This is my test string search_string
Test 12 This is This is my test string search_
Test 13 This is This is my test string search_
Test 14 This is This is my test string search_string
Test 15
Test 16 This is
Test 17 This is This is my test string search_
Test 18 This is This is my test string search_
Test 19
Test 20 This is This is my test
Test 21
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示例2

#!/bin/sh

str="This is This is my test string search_string"  #被测试字符串
subStr="This is "                                   #待替换的字符串
replaceStr="TTT "                                   #替换的字符串

echo -e "Test 1 ${str/$subStr/$replaceStr}"
echo -e "Test 2 ${str//$subStr/$replaceStr}"
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其输出为：

Test 1 TTT This is my test string search_string
Test 2 TTT TTT my test string search_string
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Reference

HTML 版本：Advanced Bash-Scripting Guide -10.2. Parameter Substitution
PDF 版本：Advanced Bash-Scripting Guide P133页