Bash has a few conditional expressions, of which you can use one to check if a variable is empty or not. That is the-zoperator. Using the-zoperator followed by a variable will result in trueif the variable is empty. The condition will evaluate to false if the variable is not empty. ...
In both examples, we used the if statement with the -z option to check if the variable is empty. Here, the -z option is a unary test operator that checks if the string is empty. This operator accepts one argument that is a string to be tested; it returns true (0 exist status) if...
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:...
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 [[ $( echo"1" ...
x="Non-empty variable" if [[ "$x" == "" ]]; then echo "x is empty" else echo "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} ]; then echo "x is not empty" else echo "x is empty" fi...
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 ...
if语句是一种条件判断语句。 首先,标准的if语句的语法是不含中括号的。 其语法如下: if condition; then echo yes else echo no fi 即condition 的代码执行后,退出状态码为真即执行 then 后的语句, 否则,执行else后的语句。 但是需要注意一点的是,这里的真值是0,即返回状态吗为0即为真值,和其他语言0表示逻...
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...
>>> 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 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 ]。