Gossamer Forum: General: Perl Programming: syntax question

Mar 17, 2009, 7:56 PM

delicia

Enthusiast (661 posts)

Mar 17, 2009, 7:56 PM

Post #1 of 6

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syntax question

i've searched my perl books but cannot find what this means:
split (/\Q$db_delim\E/o, $input)

what is \Q and \E ???

Mar 18, 2009, 1:23 AM

Andy

Veteran / Moderator (18441 posts)

Mar 18, 2009, 1:23 AM

Post #2 of 6

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Re: [delicia] syntax question In reply to

\Q -means anything after this will NOT be treated as a regex
\E - means that anything after this WILL be treated as a regex.

For example:

Code:
$var =~ s/\Q[my test one with square brackets]/[something to change to]/;

...would replace it fine

...but:

Code:
$var =~ s/[my test one with square brackets]/[something to change to]/;

...wouldn't work, as its trying to process [my test one with square brackets] as a list of charachters =)

Cheers

Andy (mod)
andy@ultranerds.co.uk

Mar 18, 2009, 1:23 AM

brewt

Staff (4101 posts)

Mar 18, 2009, 1:23 AM

Post #3 of 6

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Re: [delicia] syntax question In reply to

Looks like Andy already answered this, but here's more info:

It does the equivalent of:

Code:
$db_delim = quotemeta($db_delim); 
split(/$db_delim/o, $input);

which just backslashes all non-word characters. It's normally used so that characters in the string that are special characters in regexes aren't used inappropriately.

Adrian

Last edited by:

brewt: Mar 18, 2009, 1:25 AM

Mar 19, 2009, 3:34 AM

Wychwood

User (182 posts)

Mar 19, 2009, 3:34 AM

Post #4 of 6

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Re: [brewt] syntax question In reply to

Quote:

which just backslashes all non-word characters

I think PHP uses a more logical version whereby only meta characters are replaced, hence the name quotemeta, and not all non-word characters like Perl.

Meta characters are:

. \ + * ? [ ^ ] ( $ )

Last edited by:

Wychwood: Mar 19, 2009, 3:35 AM

Mar 24, 2009, 1:27 PM

delicia

Enthusiast (661 posts)

Mar 24, 2009, 1:27 PM

Post #5 of 6

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Re: [Andy] syntax question In reply to

andy, when you say it "wouldn't work" do you mean it would give a syntax error, or that it wouldn't make the substitution? and was your example supposed to change the square brackets as well as the text? i guess by this i mean, it would only match the text if the text was enclosed in square brackets? syntax is making my head hurt!

Mar 25, 2009, 12:14 AM

Andy

Veteran / Moderator (18441 posts)

Mar 25, 2009, 12:14 AM

Post #6 of 6

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Re: [delicia] syntax question In reply to

Hi,

As Wychwood said, if you used one of these values in $db_delim, it would break your code:

. \ + * ? [ ^ ] ( $ )

...as they would be interpreted literally.

You would always just test it LOL

Code:
#!/usr/bin/perl 

my $db_delim ='\'; 

my @values = split (/\Q$db_delim\E/o, qq|just testing this|); 

#my @values = split (/$db_delim/o, qq|just testing this|); # without \Q and \E

etc

Cheers

Andy (mod)
andy@ultranerds.co.uk