$ cat gibberish
This is a couple
of lines of crud
$ cat gibberish | perl -Mstrict -Mwarnings -ne '
> my $x;
> BEGIN {$x = shift @ARGV; print qq{BEGIN - $x\n}}
> print qq{x = $x\n$_};' myarg
BEGIN - myarg
x = myarg
This is a couple
Use of uninitialized value in concatenation (.) or string at -e line 4
+, <> line 2.
x = 
of lines of crud
$
[download]

I wonder what is causing this.

Cheers,

JohnGG

Don't declare the $x — it's just a one-liner. Perl wraps a while(<>) { ... } loop around the code you put there (really!), so it's a new $x for every line in the file.

See for yourself:

perl -n -MO=Deparse -e 'my $x' foo
[download]

produces:

LINE: while (defined($_ = <ARGV>)) {
    my $x;
}
-e syntax OK
[download]

Thanks a lot. Indeed, with the BEGIN block, it now works.

In case someone is curious, I needed it in a shell script for a convoluted situation: to be able to un-mount a disk cleanly, I needed a smart sort on the mounted partitions of the disk.

# $dest was set to "sdb" through a shell argument 
mounted_disks=$(mount | perl -nae 'BEGIN{$d=shift}; push @m, $F[2] if 
+m{/dev/$d}; END{print join(" ", sort {length($b)<=>length($a)} @m)}' 
+$dest)
umount -l $mounted_disks
[download]

Thanks to Perl and the Perl Monks, it works.

You don't really need a loop for that, you could do it like this:

mounted_disks=$(mount | perl -le'$d = shift; print join " ", sort { le
+ngth( $b ) <=> length( $a ) } map m{/dev/$d} ? (split)[2] : (), <>' $
+dest)
[download]

Or even move the mount command into the perl code:

mounted_disks=$(perl -le'$d = shift; print join " ", sort { length( $b
+ ) <=> length( $a ) } map m{/dev/$d} ? (split)[2] : (), qx(mount)' $d
+est)
[download]

Cool alternative, even if it took me a moment to understand... Thanks.