Input:
hello enrico output:
ocirne olleh To do this, I can simply tac a file and pipe the output to rev (or the other way around), so one function that does the job is just this:
revtac() { tac "$@" | rev; } Is there a built-in function for the job?
I suspect that this could potentially break something, as it would reverse <CR> and <LF> on Windows-generated files, but I'm still interested.
No, there's no builtin function for the job.
BTW, neither tac nor rev are builtins. They are external binary programs, some *nix systems even come without them.
You can also use Perl to simulate the combo:
perl -lne 'push @lines, scalar reverse; END { print for reverse @lines }' -- file 
tac and rev where two builtins. What I meant is "something that I can find in bash", but you also specified that those two might not be provided on some systems. you can work around with a awk or sed script depending on your real needs for example :
sed '/\n/!G;s/\(.\)\(.*\n\)/&\2\1/;//D;s/.//' /path/YOURFILE | sed '1!G;h;$!d' I tested it in that way :
$ cat /tmp/a hello enrico $ sed '/\n/!G;s/\(.\)\(.*\n\)/&\2\1/;//D;s/.//' /tmp/a | sed '1!G;h;$!d' ocirne olleh $ 
rev and tac, I guess there's little point in using it instead of those two. But I'll really take time to look a bit more into the first command ;) sed is found on any POSIX-compliant system (or that at least tries to comply), while rev and tac aren't among the standard utilities (This does not mean that they can't be found on non-GNU/Linux systems, though). Or awk:
awk ' function rev(s, t,i) { for (i = length(s); i > 0; i--) t = t substr(s, i, 1) return t } { line[NR] = rev($0) } END { for (i = NR; i > 0; i--) print line[i] } ' file 2 more options:
$ echo -ne foo-bar-spam-1-2-3\nNextLine\nOneMoreLine\n | tac -rs. eniLeroMen OeniLtxe N3-2-1-maps-rab-oof⏎ $ echo -ne foo-bar-spam-1-2-3\nNextLine\nOneMoreLine\n \ | python -c 'import sys ; print("".join(reversed(sys.stdin.read())), end="")' eniLeroMenO eniLtxeN 3-2-1-maps-rab-oof⏎ 
revalready breaks CRLF line endings.