grep = print lines matching a pattern less = view the contents of a text file wc = print the number of newlines, words, and bytes in files cat = concatenate files and print on the standard output find = search for files in a directory hierarchy sort = sort lines of text files uniq = condense duplicate lines
awk = pattern scanning and text processing language lsof = list open files xargs = build and execute command lines from standard input
The Pipe Character
The pipe is the vertical bar, '|', it allows you to send the output from one command, as input to a second command. It allows you to combine two or more commands to process data using combinations of commands. It is very useful, but requires you to have a strong understanding of the commands that you're going to combine. As you use the command line more, you'll become more familiar with the commands and you'll start to understand which commands make sense to pipe together and which ones don't. Each side of the pipe is a an individual statement, with a command, possible options and possibly some other information that the command needs.
Example 1 - Count the number of files in the ~/examples directory
'ls ~/examples' returns
adv_cli bash_script basic_commands c_example media_example
'wc -w' counts the number of words (words are sets of characters surrounded by whitespace).
So, when you combine the two you are counting the number of files that were listed.
diskless241@gimpy:~$ ls ~/examples | wc -w 7
Example 2 - List the files in the /home directory, excluding files with the word "diskless" or "build" in them.
The following command lists all of the directories in the /home directory in the long format, except for directories with the words "diskless" or "build" in them.
diskless240@gimpy:~$ ls -l /home | grep -vE "diskless|build" total 1348 drwxr-xr-x 3 ass ass 4096 2007-08-26 19:05 ass drwxr-xr-x 3 chin chin 4096 2007-02-06 17:17 chin drwxr-xr-x 2 clout clout 4096 2007-05-26 14:51 clout drwxr-xr-x 3 dave dave 4096 2007-02-06 17:17 dave drwxr-xr-x 15 earthworm earthworm 4096 2007-08-17 17:59 earthworm drwxr-xr-x 3 freyley freyley 4096 2007-02-06 17:17 freyley drwxr-xr-x 2 joren joren 4096 2007-02-06 17:17 joren drwxr-xr-x 3 lmoore lmoore 4096 2008-01-04 12:22 lmoore drwxr-xr-x 3 matteo matteo 4096 2007-08-28 16:12 matteo drwxr-xr-x 12 oem oem 4096 2007-02-06 16:47 oem drwxr-xr-x 2 root root 20480 2007-11-04 11:16 oldstudents drwxr-xr-x 21 receiving receiving 4096 2007-03-24 18:40 receiving drwxr-xr-x 33 reception reception 4096 2008-04-05 10:48 reception drwxr-xr-x 3 rfs rfs 4096 2008-03-27 13:13 rfs drwxr-xr-x 5 rwlove rwlove 4096 2008-03-22 14:30 rwlove drwxr-xr-x 13 ryan52 ryan52 4096 2008-03-27 13:16 ryan52 drwxr-xr-x 3 something15525 something15525 4096 2007-12-15 12:50 something15525 drwxr-xr-x 3 sparrow sparrow 4096 2007-02-06 17:17 sparrow drwxr-xr-x 10 stillflame stillflame 4096 2008-03-07 11:15 stillflame drwxr-xr-x 4 vagrant vagrant 4096 2008-02-20 00:59 vagrant drwxr-xr-x 3 wren wren 4096 2007-02-06 17:17 wren
- Run 'dmesg', pipe it to 'sort' and then to 'uniq'