Thrown a problem at work to edit a customer configuration file. Though I've whipped up something that seems to work, my Perl has become quite rusty, so I seek suggestions for better ways to do it.

Though the precise syntax of this configuration file is unknown, I've got an example configuration file, shown below. One approach is write a formal parser. The other extreme is to hack out some regexes. I've taken a middle ground, crudely parsing the VIEW records by matching with \G in harness with the /gc regex match modifier, then applying substitution regexes to modify each VIEW record.

To keep the sample code smallish, assume the goal is to change field values of "REGION" to "LOCATION" and "RUBBISH" to "TRASH" but only if the RECORD value in the VIEW is either "ABC" or "XYZ". The test program is shown below: 

# ptest.pl
#
# Sample program to edit a configuration file.
# This configuration file lacks a formal syntax specification;
# the example configuration below is all I've got.
# All fields should be treated case insensitively.

# The goal is to change field values of:
#   "REGION"  to  "LOCATION"
#   "RUBBISH" to  "TRASH"
# but only if the RECORD value in the VIEW is either "ABC" or "XYZ".

# If you run with:
#   perl ptest.pl >1.tmp 2>2.tmp
# 1.tmp will contain original file, 2.tmp will contain the changed ver
+sion.

use strict;
use warnings;

my $s_in = <<'GROK';
# comment line
VIEW View1
   RECORD           "ABC"
   FIELD            (
      FIELD            "TYPEFROM"
      FIELD            "REGION"
      FIELD            "RUBBISH"
   )
   INTERVAL         600 SECONDS
END_VIEW
VIEW View2
   RECORD           "HELLO"
   FIELD            (
      FIELD            "TYPETO"
      FIELD            "REGION"
      FIELD            "RUBBISH"
   )
   INTERVAL         700 SECONDS
END_VIEW
# random line 1
VIEW View3
   RECORD           "XYZ"
   FIELD            (
      FIELD            "FLD1"
      FIELD            "Region"
# random line 2
      FIELD            "Rubbish"
   )
   INTERVAL         800 SECONDS
END_VIEW
# random line 3
GROK

# Ensure properly newline terminated
substr( $s_in, -1 ) ne "\n" and $s_in .= "\n";

my @recs = ( 'ABC', 'XYZ' );
my %fldmap = (
   REGION  => 'LOCATION',
   RUBBISH => 'TRASH',
);
my $fldstr = join '|', keys %fldmap;

print $s_in;

my $s_out;
while (1)
{
   # Extract VIEW ... END_VIEW block
   if ( $s_in =~ /\G(^[ \t]*\bVIEW\b.*?^[ \t]*\bEND_VIEW\b)/msgic )
   {
      my $view = $1;
      # Check for matching RECORD in VIEW block
      if ( $view =~ /^[ \t]*\bRECORD\b[ \t]*"(.*?)"/mi )
      {
         my $rec = $1;
         if ( length($rec) && grep( /^\Q$rec\E$/i, @recs ) )
         {
            # Translate fields
            $view =~ s/(\bFIELD\b[ \t]*?")($fldstr)"/$1 . $fldmap{uc($
+2)} . '"'/gie;
         }
      }
      $s_out .= $view;
   }
   elsif ( $s_in =~ /\G(.*\n)/gc )
   {
      $s_out .= $1;
   }
   else
   {
      last;
   }
}

warn $s_out;

[download]

Updated: Minor changes made to code: ensured input file properly newline terminated plus very minor tweaks to regex.

In reply to Parsing and editing a configuration file by eyepopslikeamosquito

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