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...
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" ...
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 string is empty. For this, we have used the “-z” option within the square brackets...
>>> 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 $? 1>>> local defined_and_empty="" >>...
STRING True if string is not empty. 即,test命令使用-z STRING操作符来判断STRING字符串的长度是否为 0。 如果为 0,就是空字符串,会返回 true。 具体写法是test -z STRING,使用[命令则写为[ -z STRING ]。 -n STRING操作符判断STRING字符串的长度是否为 0。
# 脚本将会尝试运行"value"命令,同时设置环境变量"VARIABLE"为""。 上面$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 "${bxxx}" = "xxx" ] # 这里的判断会有单独的文章介...
TestFile1 does not exist or is empty. 向文件添加一些内容,然后再测试一次: [student@studentvm1 testdir]$ File="TestFile1" ; echo "This is file $File" > $File ; if [ -s $File ] ; then echo "$File exists and contains data." ; else echo "$File does not exist or is empty." ...
如果if结构使用的不是test命令,而是普通命令,比如上一节的((...))算术运算,或者test命令与普通命令混用,那么可以使用 Bash 的命令控制操作符&&(AND)和||(OR),进行多个命令的逻辑运算。$ 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。
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...