-z is the second supported bash string comparison operator used to check if a string is empty or not. The -z operator functions similarly like -n operator. Below is an example: Most importantly, you should add spaces around the square brackets. If there are no spaces, bash will complain ...
true if the String is not empty and not null 判断是否null、空串或空白串 是null或空串或空白串:方法一 if (s == null || s.length() == 0 || s.trim().length() == 0) { // do something } 是null或空串或空白串:方法二 if (s == null || s.matches("\\s*")) { // do som...
Test if string has non whitespace characters in Bash, The backquotes execute the command within; bash line parsing convert tabs and newlines to blanks and joins double blanks. The echo command re-emits this string, which is shrunk to an empty string for the final test by [[ ]]. I think...
{iftest-n$1;thenecho'(1) -n $1 :'"No quote: not empty."fiif[ -z$1];thenecho'(2) -z $1 :'"No quote: empty."fiiftest-n"$1";thenecho'(3) -n "$1":'"Quote : not empty."fiif[ -z"$1"];thenecho'(4) -z "$1":'"Quote : empty."fi} empty_string"$1" 这个脚本...
if [[ -n $String ]]; then echo "The variable String is not an empty string." fi 输出: The variable String is not an empty string. 在这个程序中,String 是一个非空变量。由于 -n 运算符返回 true,如果 string 的长度不是 0,因此我们得到 The variable String is not an empty string. 作为...
!=: Not equal to -z: Empty string -n: Non-empty string 3. File and Directory Checks: -e: Exists -f: Regular file -d: Directory -r: Readable -w: Writable -x: Executable Example of using If Statement: Let’s illustrate the usage of if statements with a few examples: ...
if [ "$string1" != "Not MyString" ] then echo "Not Equal Strings" else echo "Stringis equal" fi 在Bash 中检测字符串是否是空值或者空串 和那些个与 C++ 类似的语言不同,在 Bash 脚本中还可以用一个命令来检测一个字符串是否是空值(null)或者空串(empty""): ...
function empty_string() {iftest -n $1; then echo'(1) -n $1 :' "No quote: not empty."fiif[ -z $1]; then echo'(2) -z $1 :' "No quote: empty."fiiftest -n "$1"; then echo'(3) -n "$1":' "Quote : not empty."fiif[ -z "$1"]; then ...
Bash技巧:对比 test判断字符串是否为空的用法,#!/bin/bashfunctionempty_string(){iftest-n$1;thenecho'(1)-n$1:'"Noquote:notempty."fiif[-z$1];thenecho'(2)-z$1:'"Noquote
iftest"$abc";thenecho"It's not an empty string."elseecho"It's an empty string."fi 运行上面代码的输出结果为: It's an empty string. 这是因为我们没有定义变量 abc ,所以 "$abc" 被解释成了空字符串。 其实使用检查空字符串的运算符 -n 会让代码具有更清晰的含义: ...