-z STRING Trueifstring is empty. -n STRING STRING Trueifstring is not empty. 即,test命令使用-z STRING操作符来判断STRING字符串的长度是否为 0。 如果为 0,就是空字符串,会返回 true。 具体写法是test -z STRING,使用[命令则写为[ -z STRING ]。 -n STRING操作符判断STRING字符串的长度是否为 0。
functiontest_empty_string(){ test-n$1&& echo 'not null' ||echo 'null string' } test_empty_string""#return "not null" 总会得到 not null 的结果,无论调用函数时传入什么参数(包括空字符串)。 修改方法:将 test 语句改为: test -n"$1",就差了一个双引号,导致test检测失败。 所以,如果需要进行...
isvalidip() #@ USAGE: isvalidip DOTTED-QUAD { case $1 in ## reject the following: ## empty string ## anything other than digits and dots ## anything not ending in a digit "" | *[!0-9.]* | *[!0-9]) return 1 ;; esac ## Change IFS to a dot, but only in this functio...
Let’s look at another option, “-z”, used so far in Bash to check for the empty string. The code has been started with Bash support, and we have initialized a string variable “v” with the value “Hello” in it. Then, we started the “if-else” statement to check whether the ...
Unsetting BASH_XTRACEFD or assigning it the empty string causes the trace output to be sent to the standard error. Note that setting BASH_XTRACEFD to 2 (the standard error file descriptor) and then unsetting it will result in the standard error being closed. COLUMNS Used by the select ...
" Condition returned 1 # Variable is set and exist [me@linux ~]$ myVar="test" [me@linux ~]$ [[ -v myVar ]] ; echo "Condition returned $?" Condition returned 0 # Variable is set to a zero length string (null/empty) and exist [me@linux ~]$ myVar= [me@linux ~]$ [[ -v ...
查看变量中的数据时,需要在变量名前加$号,如果没有加,则echo认为其是一个字符串: $ echo TERM TERM 在echo命令中,变量被双引号" "括起来,会显示变量的数据;如果被单引号' '括起来...设置变量使用变量名=值的格式来为变量赋值,需要注意的是=左右没有空格: $ zhang=
How to find whether or not a variable is empty in Bash如何检查bash中的变量是否为空? 相关讨论 什么样的壳牌剧本?尼克斯? 贝壳脚本 Serverfault.com/questions/753/… 如果一个变量设置在Bash中,则如何复制检查的可能吗? Related Post:test for non-零length string in Bash:$n$var"vs"$var. 在...
Exercise 1: Write a bash shell script that checks the length of the string provided to it as an argument. If no argument is provided, it prints 'empty string'. Exercise 2: Write a shell script that checks whether a given file exists or not. You can provide the full file path as the...
Search for empty strings with the-zoperator by following the steps below: 1. Create a new Bash script and copy the lines below: #!/bin/bash VAR='' if [[ -z $VAR ]]; then echo "The string is empty." fi 2. Save and run the script: ...