-z STRING:字符串的长度为0 the length of STRING is zero 上面的2项,可以对字符串是否为空字符串判断,如果字符串为空(不是空字符串),无论是-n还是-z都是true STRING1 = STRING2 the strings are equal STRING1 != STRING2 the strings are not equal 示例: #! /bin/bash str1="str1" test -n ...
Let's see some other commands that could help you to test the string length in bash. One of these commands is the expr command. It has several options that are useful for string options. Among them, length gives you the length of a string. abhishek@handbook:~$ expr length "my string"...
echo "$a : The string is not empty" else echo "$a : The string is empty" fi 结果 abc = efg: a != b -n abc : The string length is not 0 abc : The string is not empty 文件测试运算符 实例: #!/bin/bash file="/home/shiyanlou/test.sh" if [ -r $file ] then echo "The ...
如果if结构使用的不是test命令,而是普通命令,比如上一节的((...))算术运算,或者test命令与普通命令混用,那么可以使用 Bash 的命令控制操作符&&(AND)和||(OR),进行多个命令的逻辑运算。$ 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。
$ man test -n STRING the length of STRING is nonzero STRING equivalent to -n STRING 也就是说此时的foo,等价于"foo",等价于 -n "foo",长度是3肯定不等于0,所以表达式总是返回true,而和函数foo没有任何关系了。 小结 if语句调用外部命令时,不要方括号'[]',而直接写命令(包括带参数)即可。
# Test the string manipulation functions string_length "Hello, world!" substring_extraction "Hello, world!" 4 3 string_concatenation "Bash, " "Script!" Output: ad@DESKTOP-3KE0KU4:~$ ./test1.sh Length of 'Hello, world!' is: 13 ...
string="test string" echo "${#string}" # output: 11 str1="test_str1" str2="test_str2" str3=$str1$str2 echo "$str3" # output: test_str1test_str2 # 通过 {} 提高可读性 str4="${str1}_yes" echo "$str4" # output: test_str1_yes pos=5 len=4 echo "${str4:$pos:$le...
stringObject.substr(start,length);start必须,length可选. start 是截取的开始位置的下标,从0开始算起,必须是数字.可以是负数,-1是倒数第一个字符,-2是倒数第二个字符,以此类推. length 是要截取的字符的长度,必须是数字.如果未指定,则从start位置处开始 CODESYS 字符串截取 character integer string ...
Use regex on a stringThe result of bash's regex matching can be used to replace sed for a large number of use-cases.CAVEAT: This is one of the few platform dependent bash features. bash will use whatever regex engine is installed on the user's system. Stick to POSIX regex features if...
Here is another option, “-n”, to check whether the specified string is empty or not. It works on the rule of checking the length of a string by counting the string characters in it. If the length of a particular string turns out to be other than zero, it will return “true”; ...