| System administrators frequently utilize
the
head
and
tail
commands to quickly check portions of text files
that they do not need to view in their entirety.
Using the head
Command
The head
command is used to display the
first n lines of one or more text files. The first ten lines are
displayed by default if the -n option is omitted. The head
command is useful when you only
want to check the first few lines of a file regardless of its length.
Figure uses the head
command to display the first
five lines of the /usr/dict/words file.
The
head
command here is used by itself,
but is typically used in a command line containing several commands in
a pipeline. This will be covered later in the course.
| Command Format: |
| head
[ -n ] filename(s) |
Using the tail
Command
Use the tail
command to display the last n
lines of a text file. The last ten lines are displayed by default if the -n
option is omitted. The tail
command is useful for checking
the most recent entries in large log files. Backup utility programs
frequently write their results to a log file showing which files were
backed up and when. The final entries in a backup log file are usually
the total number of files backed up and messages indicating whether
the backup finished successfully. Backup logs can be quite large and
the tail
command allows you to check the
end result of the backup without looking at the whole file.
Like the head
command, the tail
command can be used by itself
but is typically used in a command line containing several commands in
a pipeline. This will be covered later in the course.
| Command Format: |
| tail
[ -n ] filename(s)
or tail
[ +n ] filename(s) |
The command format above shows two
options with the tail
command; -n and +n. The
-n
option displays the last n lines of the file. The +n option allows you
to start displaying lines from a specific point in a file. It starts
at the nth line in the file and displays all lines from there to the
end. The first example in Figure
shows the use of the tail
command to see the last five
lines of the /usr/dict/words file. The second example uses the +23
option to start at line 23 of the file and displays the remaining
lines.
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Interactive
Media Activity
(Flash,
90 kB) |
| |
Using
head
and
tail
In this media activity, you are logged in as user2 and your current working directory is: /home/user2. Refer to the Class File Tree Structure by clicking the 'tree' button located on the Menu Bar and type the commands that would accomplish the requested objectives.
Note: Be sure to press enter after each one. Click on step 1 to begin.
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