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Finding Files with locate

Many Linux users use the ‘find’ utility when searching for files using the command line on their system. They’ll do a simple:

find / -name 'pattern'

Really though, the power of find isn’t just in finding names of files but rather specific details about those files. For example, if you wanted to find files which are writable by both their owner and their group:

find / -perm -444 -perm /222 ! -perm /111

or perhaps find any file that’s been altered in your Download directory in the past 24 hours:

find /home/user/Downloads/ -mtime 0

As you can see, the find command is very versatile and can be used to find an array of different attributes of files. There are times though where I’m just looking for something and I don’t want to have to wait for the command to scan the entire directory tree in order to track it down. That’s where locate comes in with quick and simple results.

Using the Locate Command

Using the locate command can only be accomplished if you install the mlocate package. Most major distributions have this available. If not, head over to the mlocate homepage and install manually. Once that is accomplished, you’ll need to manually run a command to index your filesystem with it…otherwise, you’ll have to wait for the command to run automatically as it registers with cron to do so on a system level. Open an terminal and change to your root user, then execute the following:

updatedb &

This updates the mlocate database that indexes your files and forks it to the background (the ‘&’ forks it to the background). You can now logout of the terminal as root and the process will quietly work in the background.

After the command completes, using mlocate is as easy as using the locate command:

locate firefox | less

The command above will look for all files with firefox in the name and pipe the command through less so you can use the spacebar or enter key to scroll the file buffer. Of course, the reason we pipe it through less is because any file that resides in the ‘firefox’ directory will be reported in the output. While this tool isn’t as granular as the find command, it is a quick way to track down paths, directories, and files you know should exist. Since the data is indexed using the updatedb command (by cron) the results are very quick and the command does not have to scan through the filesystem to return the results.

There are plenty more advanced options via flags (such as following symbolic links, making search term case sensitive, and even using regexp). See the man page for details on how each of these options work. Play around with locate and see what you can do! It’s a powerful and quick search command!

Convert PNG to GIF via Command Line

I installed a bare bones Arch Linux system today and took a screenshot. With no graphics utilities installed, I needed a way to convert a PNG to a GIF for a Simple Machines forum template thumbnail. I figured I’d use a command line utility to help me and ImageMagick is installed by default on most distributions. A quick read through the ImageMagick manpage and I found the convert command and thought I’d share it with everyone. Use convert in the following fashion: convert [input-options] input-file [output-options] output-file

convert SMFPress.png -channel Alpha -threshold 80% -resize 120x120 thumbnail.gif

This did a quick, same-size conversion with little loss for me to display the thumbnail online. For more information on the options I used and other options that I didn’t use, take a peek at the ImageMagick Online Help Page for convert.

Adding Color to Bash List Command Part II

I previously blogged about how to add color to the ‘ls’ command utilizing an config file and alias. I then stumbled across a nugget of wisdom from a Foresight Linux user on the developers mailing list who gave a handy command that remedies some problems with missing color in a terminal.

On some distributions, the system-wide /etc/DIR_COLORS* files are removed or not present. This results in no colors being given inside of a terminal when looking for color directories and filenames. If you find yourself in this boat, try the following command to re-populate this setting:

devnet-> cd ~/
devnet-> dircolors -p >.dircolors

This should create a default profile for colors for your session if it hasn’t been done or was accidentally removed. For more information on the dircolors command try ‘man dircolors’. Please also note that dircolors command uses the environmental variable LS_COLORS to set your session.

For more information on LS_COLORS and how it pertains to the terminal/shell/cli/prompt, there are a few blog posts that do an excellent job explaining here, here and here.

Adding Color to Bash List Command

One of the things I love is being able to enter into a directory via terminal, list the contents, and quickly see which ones are executable or not and which ones are directories or are not directories IN COLOR (not everyone is perfect right?). This is specifically handy as I move through working with Slackware based distributions like the one I’m using now, Zenwalk Linux 6 and the /etc/rc.d/ directory. Most of the Red Hat based distributions out there that I’ve used have this set automatically…so I’m used to it. When I opened up a terminal in Zenwalk I found no color. A quick investigation of ~/.bashrc showed me that there are aliases set to display color…instead of ls I’d just use the letter L; 2 l’s for another option, 3 for another. It’s interesting, but not normally how I do business. See bashrc below:

devnet[~]$ cat ~/.bashrc
alias lll="ls -al --color"
alias ll="ls -l --color"
alias l='ls --color'<br />alias search='find . -name'
alias aterm="aterm -fg white -tr"
alias version='cat /etc/zenwalk-version'
alias dh='df -h'<br />export PS1='\u[\W]\$ '
export PAGER="most"<br />devnet[~]$

I don’t use those aliases much…others of you might do the ‘ll’ or ‘lll’ but it’s just not part of my routine. So, I added in just after line 4 in the code above:

alias ls='ls --color'

You can do this a few different ways…with any command line editor like emacs, vi, or nano/pico. It’s really up to you. The easiest way for new users is to use a text editor:

devnet[~]$ mousepad ~/.bashrc

This will launch the mousepad text editor in XFCE. If you’re in Gnome, try gedit. If KDE, give kwrite a try. You should see something like the following window pop up for editing:

You should see in the picture above, I’ve added in the alias needed to make me comfortable. After that, File >> Save. You’re set! Except, you may notice that when you type the command ‘ls’ there are no colors. So what gives? Well, we haven’t loaded our ./bashrc since we changed it. You don’t have to logout and back in to get things to work though…you can do this right from the terminal:

devnet[~]$ exec bash

Now try giving the ‘ls’ command a try again and you should see that it is in color. I know a lot of the more advanced Linux guys out there are probably saying, “why’d he waste a post on this! It’s easy” and you’d be right for a majority of users out there…I hope that this post finds some new user out there that may be stuck for an answer on how to do this. One final note on this as well: You will have to do this as the root user and change /root/.bashrc in order for your root user to also have color. Thanks for reading!

Read & Display Single Line of a File

Sometimes when I’m troubleshooting a PHP error and a function is called in the debugger that gives me a line number of a file to look at, I want to know what that line says without opening up the file. Using the command line, you can accomplish this in the following way:

head -n 96 filename.php | tail -n 1

This allows you to quickly display the 96th line of filename.php. Hope this helps someone like it has me.

Print Readable Man Pages

Ever wonder how you can get a man page in into a format you can read and print? There’s many methods of doing it (copy and paste is one) but one the easiest I’ve found is:

man command | col -x -b  > command.txt

Where command is the Linux command man page you want to print/view. From there, open up command.txt in your favorite gui text editor (gedit, kate) and you have a readable format that could be printed quite easily for reference.