Linux shell编程字符串比较语法

Question

是什么区别=和==比较在Linux的shell编程字符串？

也许以下代码有效:

if [ "$NAME" = "user" ]
then
    echo "your name is user"
fi

但我认为这不是一个正确的语法.它将用于比较逐字符串==.

什么是正确的？

Answer 1

单一的等于是正确的

string1 == string2

string1 = string2

如果字符串相等则为True.'='应与POSIX一致性的测试命令一起使用

NAME="rafael"
USER="rafael"
if [ "$NAME" = "$USER" ]; then
    echo "Hello"
fi

Answer 2

通常,=运算符在比较字符串时与==的作用相同.

注意:==比较运算符在双括号测试中的行为与单括号内的行为不同.

[[ $a == z* ]]   # True if $a starts with an "z" (pattern matching).
[[ $a == "z*" ]] # True if $a is equal to z* (literal matching).

[ $a == z* ]     # File globbing and word splitting take place.
[ "$a" == "z*" ] # True if $a is equal to z* (literal matching).

来源:http://tldp.org/LDP/abs/html/comparison-ops.html

Answer 3

这些页面解释了 bash 中的各种比较运算符：

• http://www.tech-recipes.com/rx/209/bournebash-shell-scripts-string-comparison/
• http://tldp.org/LDP/abs/html/comparison-ops.html
• http://www.faqs.org/docs/Linux-HOWTO/Bash-Prog-Intro-HOWTO.html#ss11.2

在第二个链接页面上，您会发现：

==

    is equal to

    if [ "$a" == "$b" ]

    This is a synonym for =.