Here's a demonstration of the join operation performed using two tools: join, which assumes a common ordering of the keys (i.e., sorted files), and AWK, which does not.

$ cat file1.txt
gene1   1234    78975
gene13  9876    ldlgfjk
$ cat file2.txt
gene1   abc
gene13  xyz
$ join -t '     ' file1.txt file2.txt
gene1   1234    78975   abc
gene13  9876    ldlgfjk xyz
$ awk 'FNR == NR { a[$1] = $2; next } { print $0, a[$1] }' \
> FS='\t' OFS='\t' file2.txt file1.txt
gene1   1234    78975   abc
gene13  9876    ldlgfjk xyz
$

[download]

And here's a ham-handed translation of the AWK idiom into Perl.

$ perl -F'\t' -lane '
>     $a{$F[0]} = $F[1], next if $#ARGV == 0;
>     print "$_\t$a{$F[0]}";
> ' file2.txt file1.txt
gene1   1234    78975   abc
gene13  9876    ldlgfjk xyz
$

[download]

I use the AWK idiom a lot. It ain't Perl, but it's darned handy.

Jim

In reply to Re: Adding a particular column from one file to a second file by Jim
in thread Adding a particular column from one file to a second file by ZWcarp

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