4.8. Viewing text files from the shell prompt
Red Hat Enterprise Linux has several applications that allow you to view and
manipulate text files at the shell prompt. These applications
are fast and best suited to manipulating the plain text files of
4.8.1. The head Command
The head command displays the beginning of a file.
The format of the head command is:
By default, you can only read the first ten lines of a file.
You can change the number of lines displayed by specifying a
The above command would display the first 20 lines of a
file named <filename>.
4.8.2. The tail Command
The reverse of head is
tail. Using tail, you
can view the last ten lines of a file. This can be useful for
viewing the last ten lines of a log file for important system
messages. You can also use tail to watch
log files as they are updated. Using the
-f option, tail
automatically prints new messages from an open file to the
screen in real-time. For example, to actively watch
/var/log/messages, enter the folowing at
a shell prompt (as the root user):
tail -f /var/log/messages
when you are finished.
4.8.3. The more Command
The more command is a "pager"
utility used to view text in the terminal window one page or
screen at a time. The [Space] bar moves forward
one page and [Q] quits.
4.8.4. Viewing Files with less
The format of the less command is:
The main difference between more and
less is that less allows
backward and single-line movement using the same navigation as
man pages: press the [Space] bar to go down one
page, the [B] to go back one page, the
directional (or "arrow") keys to move one line at a
time, and [Q] to quit.
To search the output of a text file using
less, press [/] and
enter the keyword to search for within the file.
The above command would search through the file for all
instances of "stuff" and highlight them in the
4.8.5. Viewing and creating files with
The cat command is a versatile utility.
It can be used to view text, to create text files, and to join
files. Its name is short for
concatenate, which means to combine
Using cat alone echoes on the screen
any text you enter. It will continue to do so until you exit
Entering the cat command followed by a file
name displays the entire contents of the file on the screen.
If the file is long, the contents scroll off the screen. You
can control this by using the
redirection techiniques that are
discussed in Section 4.9 Manipulating Information from the Shell.
4.8.6. The grep Command
The grep command is useful for finding specific
character strings in a file. For example, to find every reference made to "pattern" in the file
Each line in the file that includes the pattern
"pattern" is located and displayed on the screen/