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