if [ $a = "123" ] 与 if [ $a == "123 ]

魔鬼的惊叹

在有些书中说字符串判断相等用＝,如if [ $a = "123" ]，我在linux上用==,如:if [ $a == "123 ]依然可以正确运行，请问这是bash的新特性吗？
bash 版本4.2

jason680

回复 1# 魔鬼的惊叹

$ man bash
NAME
       bash - GNU Bourne-Again SHell
...
CONDITIONAL EXPRESSIONS
       Conditional expressions are used by the [[  compound  command  and  the
       test  and [ builtin commands to test file attributes and perform string
       and arithmetic comparisons.  Expressions are formed from the  following
       unary  or  binary  primaries.   If any file argument to one of the pri‐
       maries is of the form /dev/fd/n, then file descriptor n is checked.  If
       the  file  argument  to  one  of  the  primaries  is one of /dev/stdin,
       /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2,  respectively,
       is checked.
...

       string1 == string2
       string1 = string2
              True  if  the strings are equal.  = should be used with the test
              command for POSIX conformance.

       string1 != string2
              True if the strings are not equal.


   

魔鬼的惊叹

回复 2# jason680
用了linux很长时间，貌似好像还没有好好看过man bash，而且我还发现了一些新的特性，看的书貌似都有些老了
多谢多谢