paste(1)
# Concatenate input files linewise and join them by a TAB char.
paste FILE [FILE]
-d CHAR delimiter to join each line
Examples
# Read two files.
paste <(echo -e 'a1\na2') <(echo -e 'b1\nb2')
a1 b1
a2 b2
# Can read from stdin.
echo -e 'a1 a2\nb1 b2\nc1 c2\nd1 d2' | paste - -
# a1 a2 b1 b2
# c1 c2 d1 d2