string - 如何在Bash中比较字符串(How to compare strings in Bash)

Question

如何将变量与字符串进行比较（如果匹配则执行某些操作）？

  ask by Erik Sapir translate from so

Answer 1

Using variables in if statements (在if语句中使用变量)

if [ "$x" = "valid" ]; then
  echo "x has the value 'valid'"
fi

If you want to do something when they don't match, replace = with != . (如果您想在它们不匹配时执行某些操作，请将=替换= != 。) You can read more about string operations and arithmetic operations in their respective documentation. (您可以在各自的文档中阅读有关字符串运算和算术运算的更多信息。)

Why do we use quotes around $x ? (为什么我们在$x周围使用引号？)

You want the quotes around $x , because if it is empty, your bash script encounters a syntax error as seen below: (您需要在$x周围加上引号，因为如果它为空，则bash脚本会遇到语法错误，如下所示：)

if [ = "valid" ]; then

---

Non-standard use of == operator (==运算符的非标准用法)

Note that bash allows == to be used for equality with [ , but this is not standard . (请注意， bash允许==用于与[相等[ ，但这不是标准的 。)

Use either the first case wherein the quotes around $x are optional: (使用第一种情况，其中$x左右的引号是可选的：)

if [[ "$x" == "valid" ]]; then

or use the second case: (或使用第二种情况：)

if [ "$x" = "valid" ]; then