Match pattern

[MeganP]

HI,
I am newbie to Perl. I started supporting one application that has one perl program and it needs modification. It does get next record if current record doesn't match pattern. I couldn't understand the use of s* and , in the match pattern. Could some one explain me in detail, please?

next if $_ !~ /GREEN\s*\, \s*ZONE\s*\,/;

Thanks!

 

[stevexff]

Megan

\s* means 'any number of whitespace characters' where whitespace includes spaces, tabs etc. So it's looking for lines that contain a string consisting of the following pattern.

GREEN
any number of spaces, including none
comma
any number of spaces, including none
ZONE
any number of spaces, including none
comma

What do you have to change it to search for now?

 

[aardvark92]

The \s matches any whitespace character, and the * means zero or more. The [b\,[/b] matches a comma. This should match any string that has GREEN followed by a comma followed by ZONE followed by a comma, with any amount of whitespace (or none).

As an aside, I don't think the backslash is necessary before the comma.

 

[MeganP]

Thanks for your prompt reply. Previously GREEN and ZONE could find next to each other (side by side column values), but now there are two empty columns between them. If I could make the following change, Would it be suffiecient?

next if $_ !~ /PECO\s*\,\,\,\s*ZONE\s*\,/;

 

[stevexff]

Assuming that the intervening commas in the file are always contiguous, i.e. no intervening whitespace, then yes. As Aardvark has already noted, you don't need to escape the commas. Also, the default target for the regex match is $_ anyway, and unless might be more intuitive in this context, so you could reduce it to

next unless /PECO\s*,,,\s*ZONE\s*,/;

 

[aardvark92]

And in case there is whitespace between the commas, you could use

next unless /PECO\s*,\s*,\s*,\s*ZONE\s*,/;

 

[stevexff]

aardvark

Of course, that makes it worthwhile to save 3 characters by doing

next unless /PECO(\s*,){3}\s*ZONE\s*,/;

At this rate we'll have saved a megabyte by the time we retire...