On May 21, 2023, at 09:47, Jonathan Billings <billi...@negate.org> wrote:
>
>
>>
>> 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.
This is what I’d expect would happen:
$ echo boincmgr >/tmp/test.sh
$ chmod +x /tmp/test.sh
$ file /tmp/test.sh
/tmp/test.sh: ASCII text
$ /tmp/test.sh
/tmp/test.sh: line 1: boincmgr: command not found
$
So I suspect something weird is going on that isn’t being mentioned. What
happens if you run /bin/sh /path/to/script.sh (replacing my example path with
the path to your script)?
--
Jonathan Billings
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