Question

Looking for a RegEx that would match words that contains only 2 instance of same character.

So let’s say you’re looking for words that have only 2 instances of character ‘s’.

Test Tests Sam assistant pass lessclose session

So from the above it should only select “Tests” and “pass” as it’s the only words that have two instance of ‘s’

Answer 1

One way using GNU awk:

If you are only searching for two lowercase ‘s’ characters:

awk '{ for (i=1; i<=NF; i++) if (gsub(/s/,"s",$i) == 2) print $i }' file.txt

If you would like to ignore upper and lower case ‘s’ characters (i.e. match either an ‘s’ or and ‘S’), try:

awk '{ for (i=1; i<=NF; i++) { s_count = gsub(/s/,"s",$i); S_count = gsub(/S/,"S",$i); if (s_count + S_count == 2) print $i } }' file.txt

Results:

Tests
pass