Paste

Merge every two lines: cat /path/tofile.txt | paste -d " " - -

See also

• cat, tac, more, less, tail, mtail, echo, stdin, tr, column, paste, truncate, logrotate, xzcat pv, progress, sort, ncat, virt-cat, awk, join, col, fold, tee, sponge, nfs-cat, journalctl, ccat, icat, EOF, lolcat

https://stackoverflow.com/a/9605450