Using # inside qw()

Chady has asked for the wisdom of the Perl Monks concerning the following question:

just seems that I'm braindead today. Why does this piece of code break?


#!perl -w
use strict;

my @c = q' # % ( / 3 6 7 @ B C G Q R ^ s t ~ ';

print $c[2];

# breaks into :
#  Use of uninitialized value in print at test.pl line 6.
[download]

I even tried to join the array with this:


print join ('|', @c);

# results in: # % ( / 3 6 7 @ B C G Q R ^ s t ~
[download]

where am I going wrong? I guess there is something special about the characters?

The qw() operator works as far as joining the array, but breaks with -w and gives this warning.

Possible attempt to put comments in qw() list at test.pl line 4.
[download]

He who asks will be a fool for five minutes, but he who doesn't ask will remain a fool for life.

Chady | http://chady.net/

Edit by tye to change title

Comment on Using # inside qw() Select or Download Code

Replies are listed 'Best First'.
Re: Problem with Quoting by tadman (Prior) on Jul 07, 2001 at 12:08 UTC
Your use of `q` instead of `qw` is probably the issue. You are assigning a single string to @c, and then trying to extract the third value (index 2) which isn't defined. `my @c = qw' # % ( / 3 6 7 @ B C G Q R ^ s t ~ ';` It's one of those "off-by-one" letter errors. Update: LD2 helped point out that this will generate a warning "Possible attempt to put comments in qw() list" when run with '-w' and 'strict', although it does print '(' as being `$c[2]`. I'm upgrading to 5.6.1 from 5.6.0 on the test system right now just to make sure there's no additional problems. Update²: No additional problems in 5.6.1. It runs with the same '-w' warning about comments.	[reply] [d/l] [select]
Re: Problem with Quoting by Zaxo (Archbishop) on Jul 07, 2001 at 20:46 UTC
You can get rid of the warning with: `my @c = split " ", q{ # % ( / 3 6 7 @ B C G Q R ^ s t ~ };` This warning about a legal construct in `qw` seems to me like a bug in Perl. It's bad enough when gcc is helpful like that, but Perl warnings often go into some log file each time the script is run. After Compline, Zaxo	[reply] [d/l]
(tye)Re: Problem with Quoting by tye (Sage) on Jul 08, 2001 at 06:13 UTC
I'd probably write that as: `my @c= split //, q'#%(/367@BCGQR^st~';` but you could also use: `my @c= ( '#', qw' % ( / 3 6 7 @ B C G Q R ^ s t ~ ' );` Note that perlop.pod documents this right there under qw: A common mistake is to try to separate the words with comma or to put comments into a multi-line C<qw>-string. For this reason, the `use warnings` pragma and the -w switch (that is, the `$^W` variable) produces warnings if the STRING contains the "," or the "#" character. so "don't do that". /: - tye (but my friends call me "Tye")	[reply] [d/l] [select]
Re: Using # inside qw() by wind (Priest) on Aug 16, 2014 at 08:04 UTC
You can turn the warnings off for your usage of qw `use strict; use warnings; my @c = do { no warnings 'qw'; qw' # % ( / 3 6 7 @ B C G Q R ^ s t ~ ' }; print $c[2];` [download] - Miller	[reply] [d/l]
Re^2: Using # inside qw() by Anonymous Monk on Aug 16, 2014 at 08:11 UTC
Hah, these days I dd()umper everything, no warnings either :) `my @c = ( "#", "%", "(", "/", 3, 6, 7, "\@", "B", "C", "G", "Q", "R", "^", "s", "t", "~", );` [download] naturally I perltidy also	[reply] [d/l]


We don't bite newbies here... much
	PerlMonks