From: John Johnson <johnatl@...>
Date: 2006-06-24T04:09:15+09:00
Subject: Parsing files

One thing I find myself doing over and over is parsing some type of  
text file and making something sensible out of it.
As yet, I haven't found a good solution (I'm probably missing some  
gems or modules someone has already created). I think that, though  
BNF is fine for writing compilers, it's a little more complex than  
need be for parsing files. I've recently created a solution (with  
thanks to the author of OptionParser for the modus operandi). The  
following is part of a routine for parsing some really horrid SAP R/3  
files:

# horrid file
VERSION
100
DEBUG
0
SYSTEM
PRD
HOSTNAME
198.203.4.202
SYSNUM
01
...
CONTAINER_ELEMENT_INFO
BASEUNITOFMEASURE               000002003C
CONTAINER_ELEMENT_VALUE
EA
CONTAINER_ELEMENT_INFO
CAUSECODEGROUP                  000000008C
CONTAINER_ELEMENT_VALUE
CES

# Parsing routine using my parser module
     DOTTED_QUAD_RE = '(\d+)\.(\d+)\.(\d+)\.(\d+)'
...
     @wrk = RegexpParser.new

     @wrk.on( /VERSION\n(\d+)\n/m ) { |version| @version = version }
     @wrk.on( /DEBUG\n(\d+)\n/m ) { |debug| @debug = debug }
     @wrk.on( /SYSTEM\n([^\n]+)\n/m ) { |system| @system = system }
     @wrk.on( /HOSTNAME\n#{DOTTED_QUAD_RE}\n/m ) { |hostname|
       @hostname = hostname
     }
...
     @wrk.on(
       /CONTAINER_ELEMENT_INFO\n
       ([^\s]+)                    (?# element name )
       \s+
       (\d{4})                     (?# unknown digits )
       (\d{2})                     (?# index number)
       (\d{3})                     (?# field width )
       C\n                         (?# trailing literal C )
       CONTAINER_ELEMENT_VALUE\n
       ([^\n]+)\n                  (?# value of the element )
       /mx
     ) { |name, unknown, index, width, value|
         case name
         when /REQUIREDSTARTDATE/, /REQUIREDEND/, /DATESENT/,
           /CONTRACTSTARTDATE/, /CONTRACTENDDATE/
           value = yyyymmdd_to_datetime(value)
...
         if @elements[name].nil?
           @elements[name] = []
         end
         @elements[name][index] = value
     }

Is there a better way to do this?
Should I share my parser with others (via RubyForge or the like)?

Thanks,
   JJ


---
Help everyone. If you can't do that, then at least be nice.