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From: Corentin Peuvrel <cpeuvrel@pom-monitoring.com>
Newsgroups: gnu.bash.bug
Subject: Comparison problem with case modification expansion in bash-4.3
Date: Tue, 3 Nov 2015 15:03:56 +0100
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Hi,

I think I found a bug in bash-4.3 (4.3.42 in fedora 21), that seems to exists for a long time (at least from 4.1.2 in Centos 6).

I found a fairly simple way to reproduce it : you have to initialize a variable to an empty string, and do a comparaison to it while doing the case modification expansion ${var,,}

This doesn't work :
# foo="" ; [[ bar == *"${foo,,}"* ]] && echo ok

While this works fine :
# foo="" ; [[ bar == *"${foo}"* ]] && echo ok
ok

If you unset the variable, it works as we want :
# unset foo ; [[ bar == *"${foo,,}"* ]] && echo ok
ok

If the variable is not empty, it also works normally :
# foo="A" ; [[ bar == *"${foo,,}"* ]] && echo ok
ok

I hope it's not already known, but I couldn't find anything on the net.

Thank you,

Corentin Peuvrel