Linux 脚本收集

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本文介绍了Shell脚本中括号的不同用法，包括命令替换、子shell、算术运算等，并提供实用示例。此外，还展示了如何利用Shell脚本来进行文件读取和处理，特别关注于从文件中搜索特定字符串并提取相关信息。

括号的使用说明

参考：Double parenthesis with and without dollar

$(…) means execute the command in the parens and return its stdout.

$ echo "The current date is $(date)"
The current date is Mon Jul  6 14:27:59 PDT 2015

(…) means run the commands listed in the parens in a subshell. Example:

$ a=1; (a=2; echo "inside: a=$a"); echo "outside: a=$a"
inside: a=2
outside: a=1

$((…)) means perform arithmetic and return the result of the calculation. Example:

$ a=$((2+3)); echo "a=$a"
a=5

((…)) means perform arithmetic, possibly changing the values of shell variables, but don’t return its result. Example:

$ ((a=2+3)); echo "a=$a"
a=5

${…} means return the value of the shell variable named in the braces. Example:

$ echo ${SHELL}
/bin/bash

{…} means execute the commands in the braces as a group. Example:

$ false || { echo "We failed"; exit 1; }
We failed

有用脚本收集

文件读取

读取文件目录的所有文件，按行读取每个文件，判断行文字是否包含特定字符串；如果包含，通过特殊字符来split并输出想要的值。

#!/bin/sh
for filename in /home/okchem/mysqlbackup/*.sql; do
    while IFS= read line
    do
        # display $line or do somthing with $line
        if [[ $line == *"/ocf/"* ]]; then
            SUBSTRING=$(echo $line| cut -d'`' -f 2) # 用'`'来拆分,输出数组第二个
            echo $SUBSTRING
        fi
    done <"${filename}.sql"
done