string matching

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

I'm trying to match a description field from an external file and pick records that match certain patterns in that field. The piece that is baffling me is this. ...

    if ($desc =~ /;FTP*:*/)
    {
      $txn_type = 4 ;
      print "Desc before changing: $desc \n";    
....
    }
[download]

What I was expecting this to do is match fields like

;FTP : Foreign Tax Withheld

;FTP : File Transfer to server etc.

But it's picking up desc that is ;FTR :Foreign Tax Reclaim

Here's the output of the print statement in my code above

Desc before changing: ;FTR :Foreign Tax Reclaim (BASFY)

Desc before changing: ;FTR :Foreign Tax Reclaim (SIEGY)

Desc before changing: ;FTR :Foreign Tax Reclaim (DDAIY)

How is /;FTP*:*/ matching the lines above? What am I doing wrong here?

Comment on string matching Download Code

Replies are listed 'Best First'.
Re: string matching by Paladin (Vicar) on Jan 26, 2017 at 22:18 UTC
In a regex, `` means to match 0 or more of the character right before it, so the regex `/;FTP:/` means the following: Match `;` Match `F` Match `T` Match 0 or more of `P` Match 0 or more of `:` ;FTR :Foreign Tax Reclaim does indeed match `;FT` followed by 0 `P` followed by 0 `;`. If you mean to match 0 or more of any character, you want to use `.`. So your regex becomes `/;FTP.:./`. Although to be more correct, you probably don't mean "match any amount of any character", you mean "match any amount of anything that isn't a `:`". Which would be `/;FTP[^:]:./`	[reply] [d/l] [select]
Re: string matching by hippo (Archbishop) on Jan 26, 2017 at 23:31 UTC
The short answer is that you have an asterisk where you should have a space. So your `if` test might become: `if ($desc =~ /;FTP : /)` [download] The longer answer is that if you are searching for a fixed string like this it is usually both more efficient and less error prone to use index instead of a regex match in the first place. eg: `if (index ($desc, ';FTP : ') > -1)` [download] If you only want to trigger when `$desc` starts with that string (rather than containing it anywhere) then look for the index value being precisely zero.	[reply] [d/l] [select]
Re: string matching by stevieb (Canon) on Jan 26, 2017 at 22:49 UTC
Because this: `/;FTP:/` [download] ...says match any line that has a `;` followed by `FT` followed by `P` or not `P` followed up with a `:`. Essentially, you're being too greedy. Try something like: `/;FTP.?:./` [download] ...which says match `;FTP` anywhere in the line, followed by anything non-greedily (`.?`) up until it finds a `:` (you have whitespace that the `.?` registers), followed by anything, greedy.	[reply] [d/l] [select]
Re: string matching by Laurent_R (Canon) on Jan 27, 2017 at 07:14 UTC
You probably need to learn the basics of regular expressions: http://perldoc.perl.org/perlretut.html	[reply]
Re: string matching by amitvalia (Novice) on Jan 27, 2017 at 21:11 UTC
The reason I had to do that, be greedy, is because the only consistent feature of the string I'm picking up is that it has ;FTP followed by some characters depending on the trade followed by a : and then a few more words. So my goal was to match ;FTP<anything else>:<anything else>. I think I know what changes to make to my code now. Thank you all.	[reply]