On May 20, 2023, at 22:18, Michael D. Setzer II <msetze...@gmail.com> wrote:
>
>
> Recently was getting a strange error when running a script that didn't have
> #!/usr/bin/bash at top?
> free(): invalid next size (fast)
> Aborted (core dumped)
> Just adding the line fixes the issue, but not sure why??
> Have run the script before with no such error, but had been a while? Script
> was just one line? Now 2 lines.
> #!/usr/bin/bash
> boincmgr -e /home/msetzerii/BOINC -d /home/msetzerii/BOINC
So, the #! as the first two bytes of the shell script tells the OS that it is a
shell script and to invoke what follows with the file as a parameter. So in
your example, it will invoke /usr/bin/bash /path/to/script.sh.
Without the shebang (what we call ‘#!’), the OS looks at the ‘bo’ to identify
what kind of executable it is. That’s the first two bytes of the file, because
it starts with the text ‘boincmgr’.
By default, if the OS doesn’t recognize the file’s “magic number” (those two
first bytes), it executes it with /bin/sh by default. However, on your system
it thinks your executable is some sort of binary program and instead of
interpreting it as a shell script, it tries to execute as a loaded executable.
And of course, that crashes. Or maybe your /bin/sh is broken somehow as to
generate that error.
Basically, without the shebang, shell scripts will have unpredictable results.
Don’t do it.
--
Jonathan Billings
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