Can someone please explain why this command returns an error (on Solaris ksh):
if [ "(" = "(" ]; then echo 1;fi;
ksh: test: argument expected
The same using bash is OK, and echoes "1" as expected
Also, using [[ ]] is OK.
The problem seems to be the first "("
That command seems to work on my ksh.
However, IIRC in ksh it's recommended to use [[ ]] instead of [ ]. So for a portable solution, I suggest you write it as:
if [[ "(" = "(" ]]; then echo 1; fi;
Do note however that [[]] is subtly different from [] in that wildcard expansions are not done. See http://www.bolthole.com/solaris/ksh-builtins.html#test
Update
For better portability to different shells, I tend to use the built-in test command which in ksh should have the exact same effect as [[]].
if test "(" = "("; then echo 1; fi
Does it work if you change the double quotes to single quotes -- i.e.,
if [ '(' = '(' ]; then echo 1;fi;
EDITED TO ADD: I've just been able to recreate the problem with a Digital UNIX ksh. Single quotes don't work either on this platform, however escaping the brackets does work:
if [ '\(' = '\(' ]; then echo 1;fi;
According to the man page for ksh, it states:
The following characters have a special meaning to the shell and cause termination of a word unless quoted:
; & ( ) | ^ < > <newline> <space> <tab>
...and goes on to define more parsing rules. It seems that the ( is being interpreted as a special character even when quoted (oddly), hence the requirement for escaping. If you type "set -x" at the command line before you try your if, you'll see exactly what the shell is trying to do sent to stderr preceded with a '+' sign, which may help the tracing; e.g.:
$ set -x
$ if [ '(' = '(' ]; then echo 1;fi;
+ [ ( = ( ]
ksh: test: argument expected
$
$ if [ '\(' = '\(' ]; then echo 1;fi;
+ [ \( = \( ]
+ echo 1
1
$
It may be that it depends on the ksh implementation as well -- e.g., ksh-88 vs ksh-93 and later. On Digital UNIX, the implementation is ksh-88.