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" ...
bash 里面引用一个变量的过程称为 Variable Substitution,字面意思即为变量替换。和大多数的语言叫法不同,但实际用起来没啥区别。 其实上面的赋值就有不少替换了,这里我们更进一步。 代码语言:javascript 代码运行次数:0 运行 AI代码解释 # 替换,必须有美元符号 variableName="value"a='1'b=echo $variableName;# ...
./empty_string.sh: line 5: test: go: binary operator expected ./empty_string.sh: line 9: [: go: binary operator expected (3) -n "$1": Quote : not empty. $ ./empty_string.sh (1) -n $1 : No quote: not empty. (2) -z $1 : No quote: empty. (4) -z "$1": Quote ...
如果参数之间有多个空格,Bash 会自动忽略多余的空格。 $ echo this is a test this is a test 上面命令中,a和test之间有多个空格,Bash 会忽略多余的空格。 分号 分号(;)是命令的结束符,使得一行可以放置多个命令,上一个命令执行结束后,再执行第二个命令。 $ clear; ls 上面例子中,Bash 先执行clear命令,执...
For循环基本格式:for variable in list do commands done While语句基本语句格式为:while test-condition do commands done 2.5 数组 Bash中数组是通过空格符号隔开,并且是包含在()里面。引用时从序号0开始。如:Array=(23.5 27 29 31 25.7) 其中array[0]=23.5,array[4]=25.7 ...
$mvvariable showvar $ ./showvar $x is not set $ x=3$ ./showvar $x is not set $ export x=4$ ./showvar $x=4$ x=## bash中,对一个变量重新赋值,并不会从环境变量中移除该变量 $ ./showvar $x is set but empty 设置在子shell中的变量对调用它的脚本不可见。子shell包含命令替换,如...
$bashcheckvar3.shtest Conclusion Different ways to check the variable is set or unset or empty are shown in this tutorial by using various examples. Hope, this tutorial will help the users to learn the ways of testing any bash variable. ...
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 ...
String="Test" if [[ -n $String ]]; then echo "The variable String is not an empty string." fi 输出: The variable String is not an empty string. 在这个程序中,String 是一个非空变量。由于 -n 运算符返回 true,如果 string 的长度不是 0,因此我们得到 The variable String is not an empty...
TestFile1 does not exist or is empty. 现在创建一个空文件用来测试: [student@studentvm1 testdir]$ File="TestFile1" ; touch $File ; if [ -s $File ] ; then echo "$File exists and contains data." ; else echo "$File does not exist or is empty." ; fi ...