Test command

JWilliams · #1 (**permalink**) 12-03-2007

Hello,

I am trying to add some tests to existing code. The code already contains some test commands. An example is as follows...

[[ ${retCode} == 2 ]] then

Does anyone know the purpose of the double equals? I would have used a single equals sign...

bakunin · #2 (**permalink**) 12-03-2007

Barry Rosenberg ("Hands-On KornShell93 Programming", Addison-Wesley, 1998) says (p76, Table 6-2):

Quote:

[[ string = pattern ]] or
[[ string == pattern ]]

string equals pattern [...] The single equal sign operator is old-fashioned, but still supported.

I hope this clears things up.

Interestingly the man page for test in AIX 5.3 doesn't refer to any of the string operators.

bakunin

gus2000 · #3 (**permalink**) 12-04-2007

The double-equal is the correct syntax for ksh93, although it will tolerate the single-equal to be backward-compatable with ksh88. In ksh88 (the default AIX shell) the single-equal is correct, but the double-equal is sometimes tolerated. By "sometimes" I mean the currently supported AIX versions. I don't believe it will work with ksh under AIX43 (or even AIX51) but these have both been out of support for some time.

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