A solução awk :
awk '{
getline a <"file2"
split(a,A)
for(i=1;i<=NF;i++)
printf("%s_%s ", $i, A[i])
print ""
}' file1
colar + sed :
paste file1 file2 |
sed '
:a
s/\(\(^\|\s\)[^_[:blank:]]\+\b\)\s*\(.*\t\)\(\S\+\)\s*/_ /
ta
s/\s*$//
'
loop do bash :
exec 3<file1 4<file2
while read -u 3 a ; read -u 4 b
do
echo $(paste -d_ <(printf '%s\n' $a) <(printf '%s\n' $b))
done