tr

wikipedia:tr (Unix) translate characters

• https://man7.org/linux/man-pages/man1/tr.1p.html

Concatenate lines on a file:

• cat file | tr '\n' ' '
• cat file | xargs

Concatenate/merge every 2 lines:

cat /path/tofile.txt | paste -d " "  - -

cat file | tr '\n' 
tr: when not truncating set1, string2 must be non-empty

tr --help
tr: illegal option -- -
usage: tr [-Ccsu] string1 string2
       tr [-Ccu] -d string1
       tr [-Ccu] -s string1
       tr [-Ccu] -ds string1 string2

Related commands

• awk
• paste
• cut, cut -d
• column
• tr -d '\r'

See also

• tr, tr -d, cut -d, awk -F, tr -dc
• 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