Perl reserved words/special varaibles.

casperdaghost · 10-22-2013, 03:18 PM

This one liner works great. as soon as it gets to pattern, it stops
and then prints out what i need

Code:

  $ perl -n -e 'next LINE unless /pattern/; print $_'

i got it from: http://www.perl.com/pub/2004/08/09/commandline.html

Question is - LINE - is that a perl special variable?
I don't see it in the special varaible list.
If it is not - how come it does not have a dollar sign in front of it?

j-ray · 10-23-2013, 02:51 AM

In perl one can easily write programs that work fine but almost no one understands. I think LINE is a file handle but I'm not sure and I don't know how it is created. If you don't get an answer here you can post your question here:
http://perlmonks.org/

The fellows in that forum know all the gory details...

druuna · 10-23-2013, 03:34 AM

I don't think LINE is a file handle, it is a label reference.

These 2 do the same thing:

Code:

perl -n -e 'next LINE unless /foo/; print $_' infile

and

Code:

#!/usr/bin/perl
use strict ;
use warnings ;

LINE: while (defined($_ = <ARGV>)) {
    next LINE unless /foo/;
    print $_;
}

exit 0;

I have to admit that I cannot find any documentation or reference to LINE, as stated by j-ray: The perlmonks probably know all the gory details.

casperdaghost · 10-23-2013, 10:22 AM

Every time i post something at perlmonks they yell at me (type in all caps) and make me feel like a looser.

jpollard · 10-23-2013, 12:45 PM

It is documented in the Perl book: https://docs.google.com/viewer?url=h...145_Chap09.pdf

on pages 292 and 293.

The entire chapter goes over how it works - and which options provide the loops.

j-ray · 10-23-2013, 04:23 PM

Thanks for the link! I hadn't found any docs about that.

casperdaghost · 10-25-2013, 01:32 PM

It is called a label. like NEXT: GOTO:
a LABEL is a bareward followed by a colon.

casperdaghost · 10-25-2013, 03:56 PM

the documentation for the labels is here ;

http://perldoc.perl.org/perlsyn.html