检查Bash 中的变量是否为空 - 与空字符串比较 我们可以通过将其与""进行比较来检查该值是否为空。 x="Non-empty variable"if[["$x"==""]];thenecho"x is empty"elseecho"x is not empty"fi 检查Bash 中的变量是否为空 - 使用替换方法检查 如果定义了x,则表达式被替换为test,否则为null。 if[${x:+test}];thenecho"x is not empty"elseecho"x is empty"fi
function empty { local var="$1" # Return true if: # 1. var is a null string ("" as empty string) # 2. a non set variable is passed # 3. a declared variable or array but without a value is passed # 4. an empty array is passed if test -z"$var" then [[ $( echo"1" ...
>>> core__bash_version_test=true >>> set -o nounset >>> core_is_defined undefined_variable; echo $? 1Function core_is_emptyTests if variable is empty (undefined variables are not empty)>>> local foo="bar" >>> core_is_empty foo; echo $? 1>>> local defined_and_empty="" >>...
-z STRING True if string is empty. -n STRING STRING True if string is not empty. 即,test命令使用-z STRING操作符来判断STRING字符串的长度是否为 0。 如果为 0,就是空字符串,会返回 true。 具体写法是test -z STRING,使用[命令则写为[ -z STRING ]。 -n STRING操作符判断STRING字符串的长度是否...
# 脚本将会尝试运行"value"命令,同时设置环境变量"VARIABLE"为""。 上面$b和$c的区别? 实际应用的角度来说,基本没区别,都是空值。技术的角度加以区别的话,如下: 代码语言:javascript 代码运行次数:0 运行 AI代码解释 ```bash if [ -z "$b" -a "${bxxx}" = "xxx" ] # 这里的判断会有单独的文章介...
man test man expr help for help if help case … 检查变量类型(属性) declare -p 配置命令别名(alias dtype="declare -p") 其实是利用了declare 来检查属性(有些复杂变量有多个属性) #( 04/28/22@ 9:14AM )( cxxu@CxxuWin11 ):~ a=(1 2 3) #( 04/28/22@ 9:14AM )( cxxu@CxxuWin1...
Then, the if statement checks if the $count variable is zero. If the $count variable is zero, the grep output was empty, passed to the wc-1 because the pattern was not matched. The script then outputs the message No match found. to the console using the echo command. That’s all ab...
[转] Bash中的if if语法[Linux(bash_shell)] BASH IF 我使用过的Linux命令之if - Bash中的条件判断语句 关于bash中if语法结构的广泛误解 Linux 技巧:Bash的测试和比较函数(探密test,[,[[,((和if-then-else) if语法[Linux(bash_shell)] http://blog.csdn.net/ycl810921/article/details/4988778...
square brackets. If there are no spaces, bash will complain about that. Also, since any bash test without an argument will always return true, it is advisable to quote the variables so that the test will have at least an (empty) argument, irrespective of whether the variable is set or ...
TestFile1 does not exist or is empty. 向文件添加一些内容,然后再测试一次: [student@studentvm1 testdir]$ File="TestFile1" ; echo "This is file $File" > $File ; if [ -s $File ] ; then echo "$File exists and contains data." ; else echo "$File does not exist or is empty." ...