I have two files.
I want to match the 1st column of first file to 1st column of second file. If there is a match I'd like to print the 2st column of second file, if not 0.
I have tried awk (awk 'FNR==NR{a[$1]=$0;next} {print a[$1]}' 2.txt 1.txt) but it is not working.
F1.txt
A B C D E F G H I J F2.txt
A 0.5 E 1 H 0.5 J 1 Desired_output
A 0.5 B 0 C 0 D 0 E 1 F 0 G 0 H 0.5 I 0 J 1 Assuming your input files are tab-delimited:
$ join -a 1 -e 0 -t $'\t' -o 1.1,2.2 F1.txt F2.txt A 0.5 B 0 C 0 D 0 E 1 F 0 G 0 H 0.5 I 0 J 1 join the two files, ensure all lines in the 1st file are present (-a), if any fields are null then use the value "0" (-e), take the first field from the first file and the 2nd field from the 2nd file (-o), and use tab as the delimiter (-t)
If you want awk, I'd write (note the order of the file arguments)
awk 'BEGIN {FS=OFS="\t"} NR==FNR {v[$1]=$2; next} {print $1, (v[$1] ? v[$1] : 0)}' F2.txt F1.txt 