Bash 字符串比较和匹配
示例
字符串比较使用带引号的字符串==之间的运算符。该运营商否定了比较。!=
if [[ "$string1" == "$string2" ]]; then echo "\$string1 and \$string2 are identical" fi if [[ "$string1" != "$string2" ]]; then echo "\$string1 and \$string2 are not identical" fi
如果右侧没有加引号，$string1则匹配的是通配符模式。
string='abc' pattern1='a*' pattern2='x*' if [[ "$string" == $pattern1 ]]; then # the test is true echo "The string $string matches the pattern $pattern" fi if [[ "$string" != $pattern2 ]]; then # the test is false echo "The string $string does not match the pattern $pattern" fi
在<和>运算符比较在词典顺序的字符串（不存在较少的或相等或更大，或相等的运营商字符串）。
空字符串有一元测试。
if [[ -n "$string" ]]; then
echo "$string is non-empty"
fi
if [[ -z "${string// }" ]]; then
echo "$string is empty or contains only spaces"
fi
if [[ -z "$string" ]]; then
echo "$string is empty"
fi在上面，-z检查可能意味着$string未设置，或者设置为空字符串。要区分空白和未设置，请使用：
if [[ -n "${string+x}" ]]; then
echo "$string is set, possibly to the empty string"
fi
if [[ -n "${string-x}" ]]; then
echo "$string is either unset or set to a non-empty string"
fi
if [[ -z "${string+x}" ]]; then
echo "$string is unset"
fi
if [[ -z "${string-x}" ]]; then
echo "$string is set to an empty string"
fi在哪里x是任意的。或以表格形式：
+-------+-------+-----------+
$string is: | unset | empty | non-empty |
+-----------------------+-------+-------+-----------+
| [[ -z ${string} ]] | true | true | false |
| [[ -z ${string+x} ]] | true | false | false |
| [[ -z ${string-x} ]] | false | true | false |
| [[ -n ${string} ]] | false | false | true |
| [[ -n ${string+x} ]] | false | true | true |
| [[ -n ${string-x} ]] | true | false | true |
+-----------------------+-------+-------+-----------+或者，可以在case语句中检查状态：
case ${var+x$var} in
(x) echo empty;;
("") echo unset;;
(x*[![:blank:]]*) echo non-blank;;
(*) echo blank
esac[:blank:]语言环境特定的水平间距字符（制表符，空格等）在哪里。