From: Srinivas Jonnalagadda <srinivas.j@...>
Date: 2005-11-06T14:53:09+09:00
Subject: Help requested -- regexp

I have a text file with each line representing a 'record'.  The line
has tab-separated 'field=value' values.  *Note*: Not all fields are
mandatory in all records.

This text file is rather large, and is auto-dumped from another
application.

Now, I am trying to provide a quick interface to my users to query
this file.  The interface I am looking at is something on the lines of

     (field1 > 4) and ((field4 < 2.25) or (field3 > 8.0))

to be typed in the query shell.

I had first written something similar to:

   class Field

     ...

     def gen_regexp(cond)
       regexp  = "(md = /#{@name}=(.+?)/.match(_line); md and "
       regexp += cond.gsub(/#{@name}/, 'md[1].' + @converter_method) # 
'to_i'/'to_f'
       regexp += ')'
     end

     ...

   end

This 'generated' regexp would then be substituted in the place of the
corresponding parenthesized 'condition'.  Once all such substitutions
are complete, a query block is generated as:

    query_blk = eval("lambda { |_line| #{final_regexp} }")

This query block is then used in a conventional 'select' on the lines.

It worked for the likes of the example above, but started having
problems for clauses with multiple fields in each 'condition', like:

     (field1 > 4) and ((field4 < 2.25) or (field3 + field8 > 8.0))

since the above substitution logic is at an individual field level.

Suggestions please.  Thanks!

Best regards,

JS