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 configuration files.
The head command displays the beginning
of a file. The format of the head command
By default, you can only read the first ten lines of a file. You
can change the number of lines displayed by specifying a number
The above command would display the first 20 lines of a file
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
Press [Ctrl] -[C] when you are finished.
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.
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 text.
and creating files with cat
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 files.
Using cat alone echoes on the screen
any text you enter. It will continue to do so until you exit with
the [Ctrl] -[D] keystroke.
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.
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 <filename>, enter:
Each line in the file that includes the pattern "pattern" is
located and displayed on the screen/