I am writing a shell script and have come across some weird if behavior.

My question is simple, why does [[ "╝" = [█] ]] evaluate to true? Is it because they are both uncommon ascii characters? On my mac, it evaluates fine.

note: The █ does need to be in brackets.

  • 1
    Looks like a bug.
    – choroba
    Feb 14 '15 at 19:00
  • I recommend submitting a bug report.
    – 4ae1e1
    Feb 17 '15 at 3:59

The evaluation does not depend on platform (mac or other). It depends on current locale settings:

$ if [[ "╝" = [█] ]]; then echo y; else echo n; fi
$ LANG=en_US.UTF-8
$ if [[ "╝" = [█] ]]; then echo y; else echo n; fi

We can try to detect which locales matches the expression via simple script:

for i in $(locale -a)
   export LANG=$i
   echo -n "LANG=$LANG   "
   if [[ "╝" = [█] ]]; then echo yes; else echo no; fi

and see that the UTF-8 locales matches the expression. When locale is set to UTF-8 capable then bash interprets the UTF-8 characters in different way and that is the reason why the result are different.

Nevertheless I think it is a bug because it should return false even if locale with UTF-8 support is set.

  • It is a bug. And it does depend on the platform and version. I can reproduce this on my Ubuntu 14.04LTS with bash 4.3.30, but not on OS X with either system bash (3.2.57(1), back from 2007) or brewed bash (4.3.33(1)): bash -c 'LANG=en_US.UTF-8; [[ "╝" = [█] ]]' or bash -c 'LANG=C; [[ "╝" = [█] ]]' both return 1 no matter what.
    – 4ae1e1
    Feb 17 '15 at 3:56
  • Also, I tried to blame this bug on encoding but failed. Even if you disassemble both UTF-8 characters into bytes, the first string won't match the second string (considered as a [] pattern). Maybe we have to look at the source code to tell what's exactly wrong.
    – 4ae1e1
    Feb 17 '15 at 3:58
  • I submitted a bug report, but I have very limited experience in non scripting languages so I'm afraid I won't be much help in looking for the problem in the source.
    – Lattis
    Feb 17 '15 at 19:06

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