From: Robert Klemme <shortcutter@...>
Date: 2009-03-14T18:57:55+09:00
Subject: Re: regular expression / gsub question

On 13.03.2009 20:46, Joel VanderWerf wrote:
> Mmcolli00 Mom wrote:
>> Hi
>> Do you know how use a regular expression to get only the scripname from
>> the each filename below? I have long filename and I want to pull out a
>> segment "scriptname" only. I have been using a regular expression with
>> gsub for this.
>>
>> filename
>>
>> userfilename_scriptname_030109.txt
>> userfilename3_scriptname1_031109.txt
>> userfilename_scriptname0_031209.txt
>>
>>
>> The gsub didn't work because the _ on both sides causes me to delete the
>> whole filename. What would you recommend?
>>
>> stripfirstpart = filename.gsub(/*_/,"")
>> stripsecondpart = filename.gsub(/_.*/,"")
> 
> I like using #[] for this because it lets you think in terms of what you 
> want to keep rather than what you want to remove.
> 
> filename[/_(.*?)_/, 1]
> 
> The ? is there in case there are more underscores later in the filename.

AFAIK it is more robust and also more efficient to do

filename[/_([^_]+)_/, 1]

or even

filename[/_(scriptname\d*)_/, 1]

or even

filename[/\Auserfilename\d*_(scriptname\d*)_\d+\.txt\z/, 1]

In other words, rather explicitly define precisely what you want to 
match than rely on (non)greediness of repetition operators.

Kind regards

	robert