Increment field value provided another field matches a string

$ awk 'BEGIN{FS=OFS=","} $1=="FL"{++$2} 1' data.txt
NY,1
FL,6
CA,1

Intended Output:

NY,1 FL,6 CA,1

I would harness GNU AWK for this task following way, let file.txt content be

NY,1
FL,5
CA,1

then

awk 'BEGIN{FS=OFS=",";ORS=" "}{print $1,$2+($1=="FL")}' file.txt

gives output

NY,1 FL,6 CA,1 

Explanation: I inform GNU AWK that field separator (FS) and output field separator (OFS) is , and output row separator (ORS) is space with accordance to your requirements. Then for each line I print 1st field followed by 2nd field increased by is 1st field FL? with 1 denoting it does hold, 0 denotes it does not hold. If you want to know more about FS or OFS or ORS then read 8 Powerful Awk Built-in Variables – FS, OFS, RS, ORS, NR, NF, FILENAME, FNR

(tested in gawk 4.2.1)

Use this Perl one-liner:

perl -i -F',' -lane 'if ( $F[0] eq "FL" ) { $F[1]++; } print join ",", @F;' data.txt

The Perl one-liner uses these command line flags:
-e : Tells Perl to look for code in-line, instead of in a file.
-n : Loop over the input one line at a time, assigning it to $_ by default.
-l : Strip the input line separator ("\n" on *NIX by default) before executing the code in-line, and append it when printing.
-a : Split $_ into array @F on whitespace or on the regex specified in -F option.
-F',' : Split into @F on comma, rather than on whitespace.
-i.bak : Edit input files in-place (overwrite the input file). Before overwriting, save a backup copy of the original file by appending to its name the extension .bak. If you want to skip writing a backup file, just use -i and skip the extension.

SEE ALSO:
perldoc perlrun: how to execute the Perl interpreter: command line switches