On Sun, Sep 14, 2025 at 09:56:15 -0700, Mike Castle wrote: > If you do the same thing in a loop: > > > while true; do > echo "tom" > sleep 1 > done > > It does not seem to reread.
That's because of how the bash parser works. Compound commands (which include while loops) are read, parsed and executed all at once. Bash doesn't re-read the input file during the loop's execution. It won't re-read the input file until the loop terminates (this one won't, but in general, most loops do terminate). > But for a sourced file, it does not appear to reread the sourced file. I'm... not sure about that case. > I did not try all variations, like functions and what not. Function definitions count as compound commands, so the whole function definition is read, parsed, and stored in memory as a single step. Reading the input continues after that. > This is all likely documented, but spending less than 10 seconds in > bash's info doc, I did not find it. But this is all probably by POSIX > spec. Um... it's complicated. POSIX partially specifies some of this behavior, but certain decisions are shell-specific. Going from memory (I don't feel like doing the research right now), POSIX requires shells to seek to a previously saved position in the input file (script), or to behave as if they'd done so, at specific points. It has something to do with here documents, if I remember correctly. If you're really going this deep into the bash implementation details, debian-user is not the best place to do so. I suggest that you consider subscribing to the bug-bash and help-bash mailing lists. There are actual shell developers on those. As a shell *user*, my recommendation is that you simply be aware of these issues, and take them into consideration when you modify shell scripts that might be currently running. In-place modification of a script being executed is extremely dangerous, because the shell is quite likely to end up seeking to the middle of a command and executing that partial command. You want to ensure that the new script uses a new file/inode, which new instances of the program will read, while existing instances continue reading the previous file/inode.
