Consecutively regex-replace separated values - regex

Question

Reading a raster grid file into #grid containing arbitrary numbers, like
82 8 98 98 42 12 3342 321 34 34 09434 9232
(and many more of those rows).
Herein, I do like to replace some numbers, like 34 with 42.
But only single, separated numbers! Eg. I do not want to replace the 34 in 3342.
So for numbers $a (search,eg 34) and $b (replace, eg 42), my approach is
s/(^|\s)$a(\s|$)/$1$b$2/g for #grid;
But this only replaces every second of consecutive occurrences (like 34 34 34 34=>42 34 42 34), because the suffix \s is not taken into account as prefix of the next pattern.
Is there any solution for this problem, other than putting two of those commands back-to-back (which is slow for large arrays)?

Answer 1

You're looking for \b : the boundary between a word char (\w) and something that is not a word char
s/\b$a\b/$b/g
Live DEMO

Answer 2

You can set up a hash that contains your replacement pairs, and then capture each number on a line and do the replacement if that number's a hash key:
use strict;
use warnings;
my %replacements = ( 34 => 42, 8 => 100 );
while (<DATA>) {
s/(\d+)/exists $replacements{$1} ? $replacements{$1} : $1/ge;
print;
}
__DATA__
82 8 98 98 42 12 3342 321 34 34 09434 9232
97 8 8 8 27 37 34 55 19 100 8 34 07932 8
Output:
82 100 98 98 42 12 3342 321 42 42 09434 9232
97 100 100 100 27 37 42 55 19 100 100 42 07932 100
Hope this helps!