Thanks Bob for such a nice explanation and your instinct is right. It is locale problem.
-bash-3.1$ locale LANG=en_US.UTF-8 LC_CTYPE="en_US.UTF-8" LC_NUMERIC="en_US.UTF-8" LC_TIME="en_US.UTF-8" LC_COLLATE="en_US.UTF-8" LC_MONETARY="en_US.UTF-8" LC_MESSAGES="en_US.UTF-8" LC_PAPER="en_US.UTF-8" LC_NAME="en_US.UTF-8" LC_ADDRESS="en_US.UTF-8" LC_TELEPHONE="en_US.UTF-8" LC_MEASUREMENT="en_US.UTF-8" LC_IDENTIFICATION="en_US.UTF-8" LC_ALL= -bash-3.1$ And the other point you made is also right. I didn’t realize that I was using another session for comparing the result with match which ahs different locale:- -bash-3.1$ LANG=ja_JP.UTF-8 LC_CTYPE="ja_JP.UTF-8" LC_NUMERIC="ja_JP.UTF-8" LC_TIME="ja_JP.UTF-8" LC_COLLATE="ja_JP.UTF-8" LC_MONETARY="ja_JP.UTF-8" LC_MESSAGES="ja_JP.UTF-8" LC_PAPER="ja_JP.UTF-8" LC_NAME="ja_JP.UTF-8" LC_ADDRESS="ja_JP.UTF-8" LC_TELEPHONE="ja_JP.UTF-8" LC_MEASUREMENT="ja_JP.UTF-8" LC_IDENTIFICATION="ja_JP.UTF-8" LC_ALL= -bash-3.1$ I never knew that locale has effect on the behavior. We can close this bug. Thank you so much for your time and details, I have learnt new thing :) Also, thanks for correcting my regex. Thanks and Regards, Adil Mujeeb
