UNIX for Dummies Questions & Answers

$cat file.txt
name     col1     col2     col3     coln
aaaa     2323     2132     2343     6456
bbbb     4234     3243     4342     4324
cccc     3424     4342     6546     6546
dddd     3213     3213     3213     3123
eeee     3123     5453     2453     7653

$cat result.txt
name     col1     col1   col2     col2   col3     col3   coln     coln
aaaa     2323     AB     2132     AB     2343     AB     6456     AB
bbbb     4234     AB     3243     AB     4342     AB     4324     AB
cccc     3424     AB     4342     AB     6546     AB     6546     AB
dddd     3213     AB     3213     AB     3213     AB     3123     AB
eeee     3123     AB     5453     AB     2453     AB     7653     AB

awk '
        NR == 1 {
                for ( i = 1; i <= NF; i++ )
                {
                        if ( i > 1 )
                                printf $i "\t" ( i == NF ? $i RS : $i "\t" )
                        else
                                printf $i "\t"
                }
        }
        NR > 1 {
                for ( i = 1; i <= NF; i++ )
                {
                        if ( i > 1 )
                                printf $i "\t" ( i == NF ? "AB" RS : "AB" "\t" )
                        else
                                printf $i "\t"
                }
        }
' file.txt