Question

I’m writing a perl script which extracts values from one file with message definitions and uses them to update a config file.

For example:

Message Definition File (ICD.txt):

MESSAGE: FOO_TELEM
latitude [-90,90]
longitude [-180,180]
MESSAGE: FOO_FREQUENCY
airPressure [0,50]
engineSpeed [0,65500]

Where the FOO_TELEM message has members latitude with range -90 to 90 and longitude with range -180 to 180.

Config file (Config.txt):

  MessageTable
    Message FOO_TELEM
      Member latitude  DOUBLE End-Member
      Member longitude DOUBLE End-Member
    End-Message
    Message FOO_FREQUENCY
      Member airPressure ULONG End-Member
      Member engineSpeed ULONG End-Member
    End-Message
  End-MessageTable

I’d like to be able to update the config file (Config.txt) with the constraint values contained in the message definition file (ICD.txt), so that the result would look like this:

Updated Config file (Config.txt):

  MessageTable
    Message FOO_TELEM
      Member latitude  DOUBLE CONSTRAINT -90 90 End-Member
      Member longitude DOUBLE CONSTRAINT -180 180 End-Member
    End-Message
    Message FOO_FREQUENCY
      Member airPressure ULONG CONSTRAINT 0 50 End-Member
      Member engineSpeed ULONG CONSTRAINT 0 65500 End-Member
    End-Message
  End-MessageTable

I’ve tried various forms of grep to get the results I need but have been unsuccessful. Any suggestions would be greatly appreciated. I’m open to any solutions involving grep, sed and/or perl.

Answer 1

Here’s a shot at it. I’m going to double-use DATA for my files, because I shouldn’t have to write the open/close logic.

use strict;
use warnings;

my %messages;
my $current;
CONSTRAINT:
while ( <DATA> ) { 
    last CONSTRAINT if m/^---$/;
    if ( my ( $message ) = m/^ MESSAGE: \s+ ( \S+ )/x ) { 
        $messages{ $message } = $current = {};
    }
    elsif ( my ( $name, $min, $max ) 
               = m/^ (\w+) \s+ \[ \s* (-?\d+), \s* (-?\d+) \s* \]/x 
          ) { 
      $current->{ $name } = [ $min, $max ];
    }   
}
while ( <DATA> ) { 
    chomp;
    if ( my ( $msg ) = m/Message \s+ ( \S+ )/x ) { 
        $current = $messages{ $msg };
    }
    elsif (   ref( $current )
          and my ( $before, $member, $after ) 
                  = m/^( \s* Member \s+ ( \w+ ) \s+ \w+ ) \s+ (.*) /x 
          ) {
        if ( my $vals = $current->{ $member } ) { 
            $_ = "$before CONSTRAINT @$vals $after";
        }
    }
    say;
}

__DATA__
MESSAGE: FOO_TELEM
latitude [-90,90]
longitude [-180,180]
MESSAGE: FOO_FREQUENCY
airPressure [0,50]
engineSpeed [0,65500]
---
MessageTable
  Message FOO_TELEM
    Member latitude  DOUBLE End-Member
    Member longitude DOUBLE End-Member
  End-Message
  Message FOO_FREQUENCY
    Member airPressure ULONG End-Member
    Member engineSpeed ULONG End-Member
  End-Message
End-MessageTable