e36freak 1507851557 learn the syntax [ x"$foo" = x ] harkens back to very old shells when the [ command could get confused when "$foo" starts with a "-". It is very unlkely that your script will require it. See <http://mywiki.wooledge.org/BashPitfalls#pf4>
geirha 1618346398 forget
geirha 1618346408 learn The "x-hack", [ "x$var" = xval ], was used to work around some bugs in various implementations of [. See https://www.vidarholen.net/contents/blog/?p=1035