Question

I am trying to modify a config file.

I first read it into @buffer, depending on a regex match.
The modified buffer gets written back on disk, in case the file got smaller, a trunciation is done.

Unfortunatly this does not work, and it already crashes at fseek, but as far as I can say my usage of fseek conforms to perl doc.

open (my $file, "+<", "somefilethatexists.txt");
flock ($file, LOCK_EX);
foreach my $line (<$file>) {
    if ($line =~ m/(something)*/) {
        push (@buffer, $line);
    }
}
print "A\n";
seek($file,0,0); #seek to the beginning, we read some data already

print "B\n"; # never appears

write($file, join('\n',@buffer)); #write new data
truncate($file, tell($file)); #get rid of everything beyond the just written data
flock($file, LOCK_UN);
close ($file);

Answer 1

Where are your fseek(), fwrite() and ftruncate() functions defined? Perl doesn’t have those functions. You should be using seek(), print() (or syswrite()) and truncate(). We can’t really help you if you’re using functions that we know nothing about.

You also don’t need (and probably don’t want) that explicit call to unlock the file or the call to close the file. The filehandle will be closed and unlocked as soon as your $file variable goes out of scope.