Re^4: Empty File Contents before writing

[johngg]

in reply to Re^3: Empty File Contents before writing
in thread Empty File Contnts before writing

There is also a built-in function called truncate that will do what you want.

$ perl -Mstrict -Mwarnings -e '
> open my $fh, q{>}, q{rubbish} or die $!;
> print $fh qq{A longish line of text\n};
> truncate $fh, 0 or die $!;
> print $fh qq{Short\n};
> close $fh  or die $!;'
$ cat rubbish
Short
$

Update: Added example code.

[RichardK]

The help for truncate says

The position in the file of FILEHANDLE is left unchanged. You may want
+ to call seek before writing to the file.

So, any ideas why your code works without needing a seek 0?

[johngg]

You are right. I hadn't read the documentation carefully enough and hadn't spotted that. Running hexdump -C shows that a seek is indeed necessary.

$ perl -Mstrict -Mwarnings -e '
> open my $fh, q{>}, q{rubbish} or die $!;
> print $fh qq{A longish line of text\n};
> truncate $fh, 0 or die $!;
> print $fh qq{Short\n};
> close $fh  or die $!;'
$ cat rubbish 
Short
$ hexdump -C rubbish
00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |.........
+.......|
00000010  00 00 00 00 00 00 00 53  68 6f 72 74 0a           |.......Sh
+ort.|
0000001d
$

Thank you for the correction.