Q. How do I reverse lines of a file under Linux / UNIX bash shell?
A. You need to use the rev utility or command. It copies the specified files to the standard output, reversing the order of characters in every line. If no files are specified, the standard input is read.
Display one line
tail -1 /etc/passwd
Output:
dnsmasq:x:111:65534:dnsmasq,,,:/var/lib/misc:/bin/false
Reverse one line
$ tail -1 /etc/passwd | rev
Output:
eslaf/nib/:csim/bil/rav/:,,,qsamsnd:43556:111:x:qsamsnd
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{ 5 comments… read them below or add one }
and with tac (catin reverse) you can process a file from the end (reverse lines order)
i did A LOT of googling to find this out (a)
revactually reverses characters, *not* lines. If you really want to reverse the *lines* of a file, you can use this:cat -n myfile | sort -nr | cut -c 9-try:-
cat myfile | perl -e “print reverse “
tail -r myfilealas, in Linux Debian…
root@MyServer:/root# tail -r /etc/passwd
tail: invalid option — r
Try `tail –help’ for more information.
On AIX, I did find a version of tail that supports the -r option. Unfortunately, tail -r limits the output to only the last 20480 bytes of a file. If a file is larger, the output of tail is truncated. According to the man page of tail (man tail): “If the file is larger than 20,480 bytes, the -r flag displays only the last 20,480 bytes.”