sed to insert characters in a specific column

Question

Can anyone tell me how to insert chr to every character in the first column.

file in

1 34566 34765    
2 45678 45789
3 34567 34799
X 67895 66900
Y 34567 34890

file out

chr1 34566 34765
chr2 45678 45789
chr3 34567 34799
chrX 67895 66900
chrY 34567 34890

I can't figure out how to make sed -i apply to a specific column. I'm not good with the syntax so if you could break down your explanation I would be grateful. Also, would it be better to use awk for this?

Answer 1

With sed:

sed 's/^/chr/' file.in > file.out

You don't need the -i-flag because you aren't overwriting the input-file file.in.

With awk:

awk '{print "chr"$0}' file.in > file.out

Answer 2

sed 's|^|chr|' file_in > file_out

This does a substitution (s) at the beginning of each line (^) and replacing it with the characters "chr". The pipes (|) are just separators.