While digging into the details of how bash reads shell scripts, I found some indications that bash goes out of its way to support self-modifying shell scripts. As far as I can tell, after reading and executing each command, bash will seek backward and re-read the script from the byte after the end of that command, rather than executing out of buffered data previously read from the file. (For the purposes of this logic, compound commands get run as a single unit, and this logic kicks in after running the full compound command.)
I haven't found any indications that POSIX or similar require this, and other shells like dash don't have the same behavior. I also haven't found any details about this in the bash changelog or version control history. I'd like to get some more information on the history of this mechanism, if possible. What led to bash adding support for this? What version of bash first incorporated this, and has it changed over time? (I don't want to use this mechanism myself; I'm asking because I'm working on a project that needs to care about various shells' compatibility requirements, and I wanted to find out more about this unusual corner case.) Thanks, Josh Triplett
