use strict;

while (<DATA>) {
    s/( \w) /$1/g;
    print;
}

__DATA__
3851 A A G G T T
3854 A A G G T T

[download]

Or as a one liner

perl -pi.bak -e 's/( \w) /$1/g' file.dat

[download]

And if you want to use "newer" regex features, the following is shorter:

s/ \w\K //g;

[download]

In reply to Re: Loop to merge every two columns by wind
in thread Loop to merge every two columns by Renyulb28

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