More Linux Commands
You've a file residing in some dark corner of one of your partitions; where did you last see it? You just can't remember where you saved that pesky, little file. One of my most used tools for file searching is the “locate” command. It's a quick little number when it comes to sniffing out a file because it doesn't traverse your entire file system when searching, which can be painfully slow: it parses a file database to get what you're looking for (my file database is configured to update itself at 4:40 every morning; “man updatedb” for more information). Perhaps you're curious about every file or directory that contains the text “python” somewhere inside of it.
liquidbinary@arrakis:~$ locate python
Running the above command outputs a myriad of search results. In fact, there are so many that the massive amount of output scrolls by without giving me a chance to review it; my eyes glaze over, trying to keep up. To rectify this, let's do something called “piping”, which is taking the output from one program and sending it to another program to process.
liquidbinary@arrakis:~$ locate python | less
Cool, huh? The above command chain takes the output from “locate python” and pipes the output to the “less” command using the vertical bar symbol “|”. The less command takes its input and displays it one screen at a time, allowing you to scroll through the output at your leisure, so you can actually see the output without it racing by at breakneck speed.
“Piping” output from program to program gives you an extraordinary amount of control and flexibility, and makes the shell a very powerful command line environment. For example, suppose I run “ls”:
liquidbinary@arrakis:/tmp$ ls
The above fires up the “ls” command inside the “/tmp” directory; this outputs all the file names within the “/tmp” directory. What if I only wanted to output tarball files (files that end with a “.tar.gz” suffix)? I'll need some way to filter out all files that don't contain “.tar.gz”. “Grep” is a nifty little tool that searches for patterns, and, if found, will output the match. Piping the output from the “ls” to “grep” will do the trick. Watch this:
liquidbinary@arrakis:/tmp$ ls | grep .tar.gz
The output from “ls” is “piped” into “grep”. “Grep” then takes the input that it got from “ls” and searches for the pattern “.tar.gz”, and, if found, displays the match. The output is filtered and only tarball files are displayed at the shell.
The shell is a very formidable beast that awaits your every command.
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