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Greedy expression doesn't work like I expect

bobt_1234
New User

Jan 31, 2013, 3:24 PM

Post #1 of 4 (2320 views)

Greedy expression doesn't work like I expect	Can't Post

Why doesn't this regular expression work like I expect?

Code

my $line = "/document/trial_date" 
 
my ($tag) = $line =~ /\/(.+?)$/; 
print "$tag\n";

The output is "document/trial_date".
I expect to see "trial_date".

Doesn't the question mark do a "greedy" search? It should return everything from the last slash to the end of the string, I think.

wickedxter
User

Jan 31, 2013, 6:18 PM

Post #2 of 4 (2317 views)

Re: [bobt_1234] Greedy expression doesn't work like I expect [In reply to]	Can't Post

Code

my $line = "/document/trial_date"; 
 
$line =~ /.+\/(.+)$/; 
 
print $1;

this worked for me.. regex's are greedy

(This post was edited by wickedxter on Jan 31, 2013, 6:22 PM)

rovf
Veteran

Feb 1, 2013, 1:24 AM

Post #3 of 4 (2313 views)

Re: [bobt_1234] Greedy expression doesn't work like I expect [In reply to]	Can't Post

Quote

Doesn't the question mark do a "greedy" search?

No, it's the opposite. By default, * and + are greedy, and the ? makes them non-greedy.

Reason is that we want to have greediness more frequently than non-greediness.

BillKSmith
Veteran

Feb 1, 2013, 5:46 AM

Post #4 of 4 (2301 views)

Re: [bobt_1234] Greedy expression doesn't work like I expect [In reply to]	Can't Post

You question mark only makes the plus sign non-greedy. Other parts of your regex specify a match from the first slash to the end of the string. There is only one way to do this. Greediness does not make any difference in this case.

To match everything after the last slash, match all the non-slash characters at the end of the string.

Code

my ($tag) = $line =~ /\/([^/]+)$/;

This code finds the first slash that has only non-slashes after it (i.e. the last one). The parenthesis return those non-slash characters.
Good Luck,
Bill

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