replace character with increasing numbers per line - perl

Question

I have large matrix files consisting of only "0" and "a" in clolumns and I want to do what this does:
perl -pe 'BEGIN { our $i = 1; } s/a/($i++)/ge;'; < FILE > NEW_FILE
but only increment once for each line instead of every instance on each line.
So if my first line in the file is:
0 0 a a a
The perl command gives me:
0 0 1 2 3
While i would want
0 0 1 1 1
and on the next line for instance 2 0 2 0 2 and so on...
This should be possible to do with awk, but using:
'{ i=1; gsub(/a/,(i+1));print}' tmp2
just gives me 0's and 2's for all lines...

Answer 1

Just increment before, not on every substitution:
awk '{i++; gsub(/a/,i)}1' file
This way, the variable gets updated once per line, not once per record.
The same applies to the Perl script:
perl -pe 'BEGIN { our $i = 0; } $i++; s/a/$i/ge;' file
Test
$ cat a
0 0 a a a
2 3 a a a
$ awk '{i++; gsub(/a/,i)}1' a
0 0 1 1 1
2 3 2 2 2
$ perl -pe 'BEGIN { our $i = 0; } $i++; s/a/$i/ge;' a
0 0 1 1 1
2 3 2 2 2

Answer 2

You can simply replace every occurrence of a with the current line number
perl -pe 's/a/$./g' FILE > NEW_FILE

Answer 3

perl -pe'$i++;s/a/$i/g'
or if you like to increment only for lines with any substitution
perl -pe'/a/&&$i++;s/a/$i/g'
In action:
$ cat a
0 0 a a a
1 2 0 0 0
2 3 a a a
$ perl -pe'$i++;s/a/$i/g' a
0 0 1 1 1
1 2 0 0 0
2 3 3 3 3
$ perl -pe'/a/&&$i++;s/a/$i/g' a
0 0 1 1 1
1 2 0 0 0
2 3 2 2 2