A bit more info on the origins of SIFT can be found on the install page.
README:
SIFT is a simple unix shell script installer and startup for Tcl scripts. Inspired by 'exec magic' at https://wiki.tcl-lang.org/812 . All that needs to be done is to make a few substitutions to the file 'sift.installscript', and then insert it at the top of your Tcl program. A 'makesift' script can help.