Etc : Bash - cat
cat
cat is very hand command line tool for reading short text files. Try it out by going to the etc folder and use it to take a peek at some of the files there.
$ cd /etc/ $ cat debian_version 11.4 $ cat hosts 127.0.0.1 localhost 127.0.1.1 debian # The following lines are desirable for IPv6 capable hosts ::1 localhost ip6-localhost ip6-loopback ff02::1 ip6-allnodes ff02::2 ip6-allrouters $ cat timezone Europe/Dublin
$ cat motd The programs included with the Debian GNU/Linux system are free software; the exact distribution terms for each program are described in the individual files in /usr/share/doc/*/copyright. Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent permitted by applicable law.
cat's man page is brief, when using it to read files you might find these options useful..
-n, --number number all output lines -s, --squeeze-blank suppress repeated empty output lines
cat's real reason for being is to join concatenate files so lets try that out!!. Go to your sandbox directory and use the echo command.
$ cd sandbox/ (or $ cd ~/sandbox/ ) $ echo part one (prints out part one to the screen) part one $ echo part one > 1.txt (This time divert the output to the file 1.txt) $ cat 1.txt part one (Yes success, now create 2.txt and 3.txt) $ echo part two > 2.txt $ echo part three > 3.txt $ cat 2.txt part two $ cat 3.txt part three (now to join the three files together.) $ cat 1.txt 2.txt 3.txt > all.txt (and to check the result) $ cat all.txt part one part two part three
cat can also create text files ..
$ cat > roses.txt (Just hit Enter and start typing) Roses are red (Hit Enter each time to start a new line) Violets are blue Sugar is sweet And so are you
To finish the file hit Enter and then Ctrl+C which stops cat. Use cat this time with the filename to see the results.
$ cat roses.txt Roses are red Violets are blue Sugar is sweet And so are you
Maybe a bit slushy, there is an alternate ending to that poem, so to use cat to add that to roses.txt do the following...
$ cat >> roses.txt or should I say WHAT HAPPENED TO YOU (then Enter and Ctrl+D) (and to see the results) $cat roses.txt Roses are red Violets are blue Sugar is sweet And so are you or should I say WHAT HAPPENED TO YOU
Yes cat is very handy for small text files and for good measure there is tac which concatenates and prints files in reverse order.
$ tac roses.txt WHAT HAPPENED TO YOU or should I say So are you Sugar is sweet Violets are blue Roses are red