You’ve been using Linux for a while, so you must have seen or used this command before: cat. It’s used to concatenate files and print on the standard output. But do you know there is another command spelled it reversed tac? tac is like cat, but print files in reverse.
Here is an example which cat could be handy. I need to print out the last login user in reverse. (By the default, it prints the last login first.)
kenno@c2 ~ ❯❯❯ last
kenno pts/0 192.168.1.114 Sun Nov 8 11:33 still logged in
kenno pts/0 192.168.1.114 Sat Nov 7 22:25 - 22:26 (00:00)
kenno pts/0 192.168.1.114 Sat Nov 7 22:20 - 22:25 (00:05)
reboot system boot 3.14.79-117 Thu Jan 1 10:00 still running
kenno pts/0 192.168.1.114 Sat Nov 7 21:49 - 22:16 (00:27)
kenno pts/0 192.168.1.114 Sat Nov 7 14:36 - 18:36 (03:59)
kenno pts/0 192.168.1.114 Sat Nov 7 02:15 - 02:18 (00:02)
kenno pts/0 192.168.1.114 Wed Nov 4 09:58 - 09:58 (00:00)
kenno pts/0 192.168.1.114 Tue Nov 3 23:18 - 23:19 (00:00)
kenno pts/0 192.168.1.114 Sun Nov 1 14:12 - 01:25 (11:12)
Here is the output of last command with the first login user last.
kenno@c2 ~ ❯❯❯ last | tac
wtmp begins Sun Nov 1 14:12:40 2020
kenno pts/0 192.168.1.114 Sun Nov 1 14:12 - 01:25 (11:12)
kenno pts/0 192.168.1.114 Tue Nov 3 23:18 - 23:19 (00:00)
kenno pts/0 192.168.1.114 Wed Nov 4 09:58 - 09:58 (00:00)
kenno pts/0 192.168.1.114 Sat Nov 7 02:15 - 02:18 (00:02)
kenno pts/0 192.168.1.114 Sat Nov 7 14:36 - 18:36 (03:59)
kenno pts/0 192.168.1.114 Sat Nov 7 21:49 - 22:16 (00:27)
reboot system boot 3.14.79-117 Thu Jan 1 10:00 still running
kenno pts/0 192.168.1.114 Sat Nov 7 22:20 - 22:25 (00:05)
kenno pts/0 192.168.1.114 Sat Nov 7 22:25 - 22:26 (00:00)
kenno pts/0 192.168.1.114 Sun Nov 8 11:33 still logged in
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