POSIX 7: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/paste.html
Shows files side by side line by line.
Tabulation is based on the tab character, so having lines longer than the tab make this unreadable by default:
printf '1 a\n' > a
printf '1 b\n2 b b\n' > b
printf '1 c\n2 c c\n3 c c c\n' > c
paste a b c
Output:
1 a 1 b 1 c
2 b b 2 c c
3 c c c
POSIX requires - to be one of the arguments for stdin to be read.
http://stackoverflow.com/questions/8522851/concise-and-portable-join-on-the-unix-command-line
Seems to be the best tool for it:
[ "$(printf 'a\nb\nc\n' | paste -sd, -)" = 'a,b,c' ] || exit 1
tr also works somewhat, but you have to deal with the last separator.
http://stackoverflow.com/questions/8987257/concatenating-every-other-line-with-the-next
[ "$(printf 'a\nb\nc\nd\n' | paste -d, - -)" = "$(printf 'a,b\nc,d')" ] || exit 1
- - works only for stdin: http://stackoverflow.com/questions/8987257/concatenating-every-other-line-with-the-next#comment50617700_8987307