It could be done pretty simply with a one-liner if I understand the issue correctly (untested):

perl -pi.bak -e "s/(SW_V)[\d.]+/${1}02.05/" filename.txt
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For the record, the -i switch handles "in-place editing", but it does so in a way that is pretty safe. It actually writes a new outfile, and then renames the input file to whatever.bak, and then renames the output file to the name of the old input file. If you wanted to do it by hand (ie, not as a one liner, and not using the -i switch), you would probably just open the input file and the output file and later use rename to handle the filename swap. ...seems superior to a read/write filehandle.

Another potential solution is to use Tie::File, and then just wend your way through the array, performing the substitution when the version string is encountered. Tie::File handles the dirty details of in-place editing for you.

I think you could make the solution more general by incrementing what you find in the pattern although this would break if the major version changed or they got to SW_V02.100.

perl -pi.bak -e 's/(SW_V02\.)(\d\d)/$1 . sprintf("%02d", $2 + 1)/e;' f
+ilename.txt
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You may need to change my quotes if not working on Unix.

Cheers,

JohnGG

A neater regex: s/(?<=SW_V)[\d.]+/02.05/

Another safeguard would be to specify that the substitution may happen only once per file. Assuming there is at least one appearance of a version string in the file, and most likely, it's near the very top of the file, that should work and protect you reasonably well.

I'm thinking that the easiest way to achieve that is to simply slurp the whole file, and process it with a single s///. Source files are usually short enough to not pose any problems. According to perlrun you can use the -0777 switch to slurp the whole file (that's a zero, not a capital O, BTW. I always make that mistake.)

use IO::InSitu;

my ( $src, $dest ) = open_rw( 'my_file', 'my_file' );

while ( my $line = <$src> ) {
   # If this is the line you want to modify
   # Call a routine to modify either the minor or
   # major version, depending on the case in question
   # by modifying $line
   print {$dest} $line;
}
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