今天突然发现grep -q 用于if 逻辑判断很好用。
-q 参数，本意是 Quiet; do not write anything to standard output. Exit immediately with zero status if any match is found, even if an error was detected. 中文意思为，安静模式，不打印任何标准输出。如果有匹配的内容则立即返回状态值0。
小应用
# cat a.txt
nihao
nihaooo
hello
# if grep -q hello a.txt ; then echo yes;else echo no; fi
yes
# if grep -q word a.txt; then echo yes; else echo no; fi
no
-q 参数，本意是 Quiet; do not write anything to standard output. Exit immediately with zero status if any match is found, even if an error was detected. 中文意思为，安静模式，不打印任何标准输出。如果有匹配的内容则立即返回状态值0。
小应用
# cat a.txt
nihao
nihaooo
hello
# if grep -q hello a.txt ; then echo yes;else echo no; fi
yes
# if grep -q word a.txt; then echo yes; else echo no; fi
no
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