In this article I am going to introduce you to the grep command and how it is used. Once you know this command, your life with the Linux command line will be made much easier.

Limitations

Although grep is a very versatile command to know, it does have its limitations. One of the biggest limitations it has is that it can not search within binary files. That’s all fine, because your typical binary file would be searchable with the application that created said binary file.

Grep also has a line limit of 2048 lines. This means if your file is beyond that, grep will stop searching at the line limit.

Installation

You are in luck. Grep is a tool that comes pre-installed with all Linux distributions. So no installation is required.

Usage

The basic usage of grep is:

grep [OPTIONS] [PATTERN] file

Their are numerous options to use with the Grep command. The more helpful of these options are:

-E Interpret the PATTERN section as an extended regular expression.
-P Interpret the PATTERN section as a Perl regular expression.
-e Use PATTERN as the pattern. If searching a single PATTERN you do not need the -e option. But this option allows you to search for multiple search patterns.
-f  Obtain patterns from a file, one per line.
-i Ignore case.
-c Suppress normal output and only output count of matching lines.
--color Display the matched strings in color.
-n Display the line number associated with the matching entry.

Examples

Let’s take a look at a very basic example first. You want to search the file /etc/test.conf for the string input. The grep command for this would be:

grep input /etc/test.conf

Now, let’s say that test.conf is a larger file and you need to know the line number the string input is on. For this the command would look like:

grep -n input /etc/test.conf

The above output would then include the line number associated with each matching entry. Now, let’s say you wanted to search the same file for both input and output and you want to know the line numbers associated with each. For this the command would look like:

grep -n -e input -e output /etc/test.conf

But what if you only want to know how many times the string input is found in the file /etc/test.conf. For this you could use the command like so:

grep -c input /etc/test.conf

Final thoughts

Grep is one of those commands that you will use time and again, in many, various ways. I always tell new users that, once you reach the point where you begin using the command line, grep is one of the first commands you should master.

Guake is a drop-down terminal that fits all of these needs perfectly. It’s for the GNOME environment and is easy to use and is one of those tools that, once you start using, you’ll wonder why you hadn’t been using all along. In this article I will show you how to install and use the Guake drop-down terminal so your Linux command line can be as finger-tip ready as possible.

Installation

Fortunately the installation of Guake is simple. Because it lives in the standard repositories of all of the major distributions, you can install Guake with a command like this:

yum install guake

or

sudo apt-get install guake

Figure 1

If you use the former command you will have to do so after you su to the root user. Once installed you will need to start Guake. You do so by clicking Applications > Acesssories > Guake Terminal. Once started Guake will reside in your notification area as an icon (see Figure 1). The icon is the Green downward pointing arrow. If you right-click that icon can access the Guake preferences.

Configuration

There isn’t too much to configure with Guake. From the preferences window you can take care of such items as:

• The default shell: You will most likely want to stick with the default here.
• Main window height: How tall do you want Guake when it is opened?
• Appearance: Text color/font, background color/transparency/image.
• Various keyboard shortcuts

By default Guake is not set to start up on login. One of the surprises that always catches me with Guake is you can not set this through the properties window. Instead you will have to set this through the GNOME Start up Applications tool. Access this by clicking System > Preferences > Startup Applications. When this window is open scroll down until you find the Guake entry, click the Guake checkbox, and click Close. Now Guake will start up when you log in.

Usage

Figure 3

To use Guake you simply click the keyboard shortcut configured in the Preferences window. By default that key is F12.  When you click the Open key Guake will drop down for you to use. Figure 3 shows Guake in action, running the top command. By default Guake will remain above all other windows until you dismiss it (by clicking the same key you did to open it).

You can use Guake as you would a normal terminal window. And, like most good modern terminals, you can have multiple tabs open. To open a new tab in Guake, by default, you higt <Ctrl><Shift>t.

If you want to know other handy keyboard shortcuts, go back to the Preferences window and look at the Keyboard shortcuts tab.

Final thoughts

If you frequently use the command line, you will very much be glad you have found Guake. With a terminal window so accessible, your work will be that much more efficient. And we all know efficiency is a key factor in every day computing (at least for many of us).

Simple. You use the commands that have been around since the early days of Linux: shutdown, reboot, and startx. In this article I will introduce you to these commands so you will have a solid understanding of how they are used.  And hopefully the shutdown and reboot commands will rarely (if ever) be used.

Startx

Let’s begin with the startx command. This command is rarely used now, because most all distributions boot into graphical mode. But there are occasions where you will want to have a GUI-enabled machine stop at console login. And when you do have to get to that GUI running, you need to know startx.

Generally speaking the use of startx command is simple. After you log in you issue, aptly enough, startx. This command will bring up your GUI. The starx command is actually a “front end” for the xinit system and allows a single instance of the X Windows system to start. One neat trick with startx is that you can add an .xinitrc file to your ~/ directory to tell startx which desktop environment to run. Say you want to run KDE. For this your .xinitrc file would contain the line:

exec startkde

Or, if you wanted to start GNOME, the line would look like:

exec gnome

You can also start just about any window manager in the same way.

Reboot

If you have a console-only machine, and you have a need to reboot that machine, the easiest way to do this is to issue the command reboot. Now in some distributions the reboot command is limited to administrator-level users. So you might have to either su to root or use the sudo command in conjunction with reboot in order to successfully reboot your machine.

Shutdown

Shutdown is a bit more complicated than reboot.  With shutdown you need to indicate a time when the process is to take place. This, of course, means you can time your shutdowns. But most often the shutdown command will look like:

shutdown -h now

The h option tells shutdown to halt the machine. Shutdown can actually reboot the machine as well (with the use of the r option). Using the now option informs shutdown that the action is to take place immediately. You can also tell shutdown to run the process at a given time. For time you can use either the +m (where m = minutes) or hh:mm (where hh is hour and mm is minutes). So if I wanted to shutdown the machine in an hour I could issue the command:

shutdown -h +60

Or, if I wanted to shutdown the machine at midnight, I could issue the command:

shutdown -h 12:00

Final thoughts

Although these commands won’t be used that often, it is wise to have them in your toolkit. You never know when you are going to be faced with the Linux console!

But because grep is so handy, it’s hard to know where to start. Of course you can use grep in the standard way, but when you can do so much with a command, why not learn some cool tricks. And that’s what we’ll do here – learn how to use grep to really make it useful.

Basic usage

Before we get into some fun stuff, we should look at the basic command structure. To use grep in its most basic form you follow this structure:

grep STRING FILE

Where STRING is the string of characters you want to search for and FILE is the file you want to search.

Say, for instance, I want to search the file test.txt for the string “Linux” (no quotes). I can do this with the command:

grep Linux test.txt

What grep will do is print out (at the prompt) every line in the file that contains the word Linux. But what if you are searching a large configuration file and you need to find the location of a specific option. To do this you can add the “n” switch which will print out the line numbers associated with each line. Let’s look at a different example. Say you need to find out what port Dansguardian listens to. Instead of scrolling through every line of the /etc/dansguardian/dansguardian.conf file for the string “port” (no quotes), you could issue the command:

grep -n port /etc/dansguardian/dansguardian.conf

which would report back something like:

6:# Web Access Denied Reporting (does not affect logging)
10:#  1 = report why but not what denied phrase
11:#  2 = report fully
14:reportinglevel = 3
17:# The HTML template within this dir is only used when reportinglevel
87:# the port that DansGuardian listens to.
88:filterport = 8080
93:# the port DansGuardian connects to proxy on
94:proxyport = 3128
97:# dansguardian reporting script was copied. Only used in reporting levels 1 and 2.
153:# the naughtyness limit will be log

So you can see that line 88 is the filter port and 94 is the proxy port. Easy. Now let’s see what else grep can do.

Lines before and after

What if you not only want to see the single line associated with a string, but also a certain amount of lines above and below that line. You can do this using the -A and -B switches like so (we’ll stick with our dansguardian example):

grep -B1 -A2 -n port dansguardian.conf

The above command would print out not only each line containing the string “port” (no quotes) but also the 1 line above it and the next two lines below it.

Pipe other commands

You remember the dmesg command. This command prints out the kernel buffer – it’s where you learn a lot about your machine. What if you want to check out CPU information in the dmesg output. You can issue the command dmesg | less and scroll around until you find it, or you can issue the command:

dmesg | grep -n CPU

which will print out all the dmesg output that contains the string CPU and the lines numbers associated with each line.

Search directories

You can also have grep help you in your search of directories. To do this you would use it in conjunction with, say, the find command. Say you were looking for the configuration file for the nano text editor but you had no idea what it was called or where it was located. You could pipe the output of the find command to grep (as the root or sudo user) like so:

find / | grep nano | less

and you would see among the output:

/etc/nanorc
Bingo! There’s your configuration file.

Final thoughts

As you can see there are a number of ways that the grep command can be of assistance. And this is only scratching the surface. Do you have a nifty way to use grep? If so, share it with your fellow ghacks members.