It seems that the single-equals is POSIX, while the double-equals is a bash extension that at one point bash preferred and extended the match behavior of.
But, the bash manpage now documents double-equals (when in the context of the builtin test or its '[' alias) as equivalent to single-equals. The manpage notes that when using test (rather than '['), one should always use single-equals, due to POSIX compatibility issues, in case the script gets run by a shell without a builtin test. Bash has another extended test, '[[', which does significantly different, and expanded, things, but its behavior was inconsistent across bash versions the last time it was relevant to my work. Apparently bash's interpretation of single-equals isn't always exactly POSIX-standard, depending on which bash settings are in effect. A quick skim shows that it may or may not be case-insensitive, may or may not be glob-active (older version), *is* glob-active (newer versions, with caveats?)... dash's behavior isn't saying "unknown operator '['". It's saying "builtin-test-via-left-square-bracket: unknown operator '=='". I think it's just phrasing it really poorly due to overly simplistic backtracking in its parser (most recent symbol being assumed to be the cause of the error, thus printed). On 2/5/18, Ryan Prichard <rprich...@google.com> wrote: > FWIW: I think the problem is the double-equals operator: > > $ /bin/dash -c 'if [ x = x ]; then echo foo; fi' > foo > > $ /bin/dash -c 'if [ x == x ]; then echo foo; fi' > /bin/dash: 1: [: x: unexpected operator > > $ /bin/dash -c 'if /usr/bin/[ x == x ]; then echo foo; fi' > foo > > POSIX hasn't specified ==. I'm guessing it's strictly equivalent to =? > > http://pubs.opengroup.org/onlinepubs/9699919799/utilities/test.html > > -Ryan > > > On Sun, Feb 4, 2018 at 6:11 PM, Rob Landley <r...@landley.net> wrote: > >> I tried adding this to configure: >> >> if [ "$(basename "$0")" == configure ] >> then >> echo "This file is just a persistent place to set environment >> variables." >> echo "You probably want to run 'make defconfig'." >> echo "Type 'make help' for more options, or see the README." >> exit 1 >> fi >> >> But if your #!/bin/sh points to the Defective Annoying SHell it >> goes "unexpected operator [" EVEN THOUGH "[" IS IN THE $PATH, >> and I'm just not going there. >> >> So I've put #!/bin/bash at the top, set the executable bit, and >> I'm keeping the complaint to one line and running "make defconfig" >> anyway on the theory making it easier to use is better than trying >> to educating people with a pop-up window error. >> >> Rob >> _______________________________________________ >> Toybox mailing list >> Toybox@lists.landley.net >> http://lists.landley.net/listinfo.cgi/toybox-landley.net >> > _______________________________________________ Toybox mailing list Toybox@lists.landley.net http://lists.landley.net/listinfo.cgi/toybox-landley.net
