Fun with vertical tab (ASCII)

flfederation

Never knew what ASCII 11 was for. Didn't know there were other shortcuts besides \n \r \t either, until I read about the "portable character set" on Wikipedia.

\v is one of them; as \n corresponds to ASCII 10 and \t to ASCII 9, \v is ASCII 11 (also Unicode).

Here's how you use it:

$ echo "vertical\vtab\vis\vfun"

This also works in GNU/Linux, but you may need -e for echo (so far, in BSD the -e doesn't error but it changes nothing that I can tell).

rvp

flfederation This also works in GNU/Linux, but you may need -e for echo (so far, in BSD the -e doesn't error but it changes nothing that I can tell).

This is why the printf(1) command exists--the echo(1) command varies too much.
If the string contains escape sequences, use printf. Or, have the shell itself evaluate escape sequences using $'...':

printf 'vertical\vtab\vis\vfun\n'
echo $'vertical\vtab\vis\vfun'

The \v character produces that output only on terminals. On printers, it is a reverse line-feed--the opposite of \n--and backs the paper up 1 line. Use the col(1) command to see that on a glass TTY:

$ printf 'vertical\vtab\vis\vfun\n' | col
             fun
           is
        tab
vertical
$ printf 'vertical\v\rtab\v\ris\v\rfun\n' | col
fun
is
tab
vertical
$

Even more fun, no? (Mis)using \v and col to implement tac(1).

flfederation

Even more fun, no? (Mis)using \v and col to implement tac(1).

Awesome! tac is one I miss the most-- I'm more than capable of whipping up an alternative, I just hadn't gotten around to it.

Your solution is elegant-- I'm so glad I posted this.

For some reason though, col is segfaulting on OpenBSD. So this is my new tac:

printf 'rev\n\is\nfun\ntoo' | tr '\n' '\r' | rev | tr '\r' '\n' | rev

rvp

flfederation For some reason though, col is segfaulting on OpenBSD.

OpenBSD, too, eh? Then that's 4 for 4. On all the OSes I tried--Ubunto 19.02, FreeBSD-12.1-RELEASE and NetBSD 9.0_STABLE--col(1) failed miserably if the input string contained no \n. On Ubuntu and FreeBSD, col segfaulted; on NetBSD it did not deign to produce any output.

At first, I thought that it was because col was tricky to implement correctly, but, it turned out to be common pedigree: All of them derive from code contributed to the original 4.x BSD.

The output you saw was on FreeBSD after I'd patched it. I've sent patches upstream for FreeBSD and NetBSD. OpenBSD and Ubuntu will probably pick it up in due course.

As for tac(1), here's mine (needs an actual file and here-strings):

$ cat foo.txt
Behold
the
power
of
mighty
ed(1).
$ ed -s foo.txt <<<$'g/.*/m0\n%p'
ed(1).
mighty
of
power
the
Behold
$

flfederation

rvp Nice, now I don't have to file a bug report!