paste 6 GNU sed

#!/bin/sed -f

# Concatenates up to 6 lines with ' '
#
#i.e.: '1\n2\n3\n4\n5\n\6\n7\n\8\n9\n10\n11\n12\n13\n14\n'
# becomes '1 2 3 4 5 6\n7 8 9 10 11 12\n13 14\n'
#
# Requires GNU extensions

: repeat
N
y/\n/ /
6~6 ! b repeat