(bbfu) (eq instead) Re3: Appending an array

boo_radley's method will work for anything (provided you use a variable instead of a literal 'webpage3'), except that you probably shouldn't use a regexp match as he did and just use eq instead, in case they, for example, type in 'webpage' (boo_radley's would match, and thus not add, even though it's technically different). Depends on how you want to handle those cases, though.

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

our @data = qw(webpage1 webpage2);

print "Webpage needed: ";      # <STDIN> flushes output buffers
chomp(my $response = <STDIN>); # <STDIN> instead of <> in case they
                               # add command line arguments

push @data, $response unless grep { $_ eq $response } @data;

print "$_\n" for @data;
[download]

(Update: Expounded upon why eq should probably be used instead of m//)

bbfu
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Fearless on my breath
Teardrops on the fire
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Re: (bbfu) (eq instead) Re3: Appending an array by Anonymous Monk on May 31, 2002 at 11:08 UTC
`push @data, $response unless grep { $_ eq $response } @data;` [download] Please advise, I understand now that the push function adds to end of list but why is the grep on the response needed? Basically what is the `grep { $_ eq $response } @data` part doing??	[reply] [d/l] [select]
Finding answers in perl (How to fish) by boo_radley (Parson) on May 31, 2002 at 14:42 UTC
This may be a good time to point out all the wonderful things that perl (including grep) can do for you. Any time you have a question about what a certain function does, you can type `perldoc -f functionname` and get a reasonably detailed explanation.	[reply]
grep in a conditional by ChemBoy (Priest) on May 31, 2002 at 16:37 UTC
What grep does is go through the list and return a sublist of elements that (in this case) are equal to the element you're about to add. That sublist is then evaluated in boolean context by the unless: if the sublist is empty, it evaluates false, and the push takes place; if it's non-empty (which is to say, if `$result` appears in `@data` already), it evaluates true, and the push is stopped. In effect, the `unless grep...` means "unless we've already seen this result": it's there to prevent you from adding duplicates to `@data`. You could filter for it later on, but it'd be a pain, so pre-filtering it makes a lot of sense. If God had meant us to fly, he would never have given us the railroads. --Michael Flanders	[reply]