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 a
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;# ...
- Test if a given variable is [eq]ual/[n]ot [e]qual/[g]reater [t]han/[l]ess [t]han/[g]reater than or [e]qual/[l]ess than or [e]qual to the specified number: [[ $variable -eq|ne|gt|lt|ge|le integer ]] - Test if the specified variable has a [n]on-empty value: ...
./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 "$1": Quote ...
square brackets. If there are no spaces, bash will complain about that. Also, since any bash test without an argument will always return true, it is advisable to quote the variables so that the test will have at least an (empty) argument, irrespective of whether the variable is set or ...
test/[ ]基本情况 ‘test’: Check file types and compare values man test(获取帮助) test的判断表达式分为4类 string integer expression file testexits with the status determined by EXPRESSION. Placing the EXPRESSION between square brackets ([and]) is the same as testing the EXPRESSI...
# 取消变量的值 unset my_variable 还可以使用环境变量为变量赋值。例如,可以使用$PATH环境变量: 代码语言:txt 复制 # 使用环境变量为变量赋值 current_path=$PATH echo "当前的PATH环境变量值为:$current_path" 参考链接: Bash变量赋值 相关搜索: linux bash 变量赋值 在bash中赋值位置变量 如何为bash中的布尔值...
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...
$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 $x is set but empty 设置在子shell中的变量对调用它的脚本不可见。子shell包含命令替换,如...
TestFile1 does not exist or is empty. 现在创建一个空文件用来测试: [student@studentvm1 testdir]$ File="TestFile1" ; touch $File ; if [ -s $File ] ; then echo "$File exists and contains data." ; else echo "$File does not exist or is empty." ; fi ...