The-zflag checks whether the string length is zero. If the string length is zero, it returns true, else it returns false: $ [ -z "sam" ] && echo "True" || echo "False" Check if strings are equals The '=' operator checks if string1 equals string2. If the two strings are equal...
This script shows a simple example of anifstatement that uses anelseclause. The conditional test checks whether the customer's age is greater or equal to 21. If it is, the customer can enter the premises, and thethenclause is executed. If they're not old enough, theelseclause is execute...
示例要跟在 "if" 之后。例如: if [ -z "$myvar" ]then echo "myvar is not defined"fi 1. 有时,有几种不同方法来进行特定比较。例如,以下两个代码段的功能相同: if [ "$myvar" -eq 3 ]then echo "myvar equals 3"fi if [ "$myvar" = "3" ]then echo "myvar equals 3"fi 1. 上面两个...
How to do string comparison and check if a string equals to a value? How to check if a string is in an array? How to use the Bash ternary operator? How to negate an if condition in a Bash if statement? (if not command or if not equal) How to use the BASH_REMATCH variable with...
scriptname=${0##*/} ## /home/chris/bin/script => script 尝试 在bash2中引入了 KornShell 93 的两个扩展:搜索和替换以及子串提取。 ${var//PATTERN/STRING}:用字符串替换模式的所有实例 因为问号匹配任何单个字符,所以本示例隐藏了一个密码: $ passwd=zxQ1.=+-a $ printf "%s\n" "${passwd//...
/bin/BashS1="Hello World"S2="Hello World"if["$S1"="$S2"]thenecho"Equal"elseecho"Not Equal"fi The following script contains two strings,S1andS2have the same value. Theifcondition compare the string using=operator; however, we can also useif [ "$S1" == "$S2" ]statement to compare...
如果if结构使用的不是test命令,而是普通命令,比如上一节的((...))算术运算,或者test命令与普通命令混用,那么可以使用 Bash 的命令控制操作符&&(AND)和||(OR),进行多个命令的逻辑运算。$ command1 && command2 $ command1 || command2对于&&操作符,先执行command1,只有command1执行成功后, 才会执行command2。
For example, here, I used an empty string to demonstrate how you can use the -z operator in a bash script: #!/bin/bash my_string="" if [ -z "$my_string" ]; then echo "The string is empty." else echo "The string is not empty." fi As the string was empty, it gave me ...
-n is one of the supported bash string comparison operators used for checking null strings in a bash script. When -n operator is used, it returns true for every case, but that’s if the string contains characters. On the other hand, if the string is empty, it won’t return true. ...
: 这一行注释将会产生一个错误,( if [ $x -eq 3] )。 它也可以作为一个域的分隔符,比如在/etc/passwd和$PATH 变量中。bash$ echo $PATH /usr/local/bin:/bin:/usr/bin:/usr/X11R6/bin:/sbin:/usr/sbin:/usr/games 将冒号作为函数名称也是可行的。