下面是一个例子，它使用的所有字符串运算：
#!/bin/sh a="abc" b="efg" if [ $a = $b ] then echo "$a = $b : a is equal to b" else echo "$a = $b: a is not equal to b" fi if [ $a != $b ] then echo "$a != $b : a is not equal to b" else echo "$a != $b: a is equal to b" fi if [ -z $a ] then echo "-z $a : string length is zero" else echo "-z $a : string length is not zero" fi if [ -n $a ] then echo "-n $a : string length is not zero" else echo "-n $a : string length is zero" fi if [ $a ] then echo "$a : string is not empty" else echo "$a : string is empty" fi
这将产生以下输出结果：
abc = efg: a is not equal to b abc != efg : a is not equal to b -z abc : string length is not zero -n abc : string length is not zero abc : string is not empty
要注意以下几点：
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运算符和表达式之间必须有空格，例如2+2是不正确的，因为它应该写成2 + 2.
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if...then...else...fi 语句在下一章节中已经解释的决策声明。
