With the grep command.

If you want to find out if the term user is in /etc/httpd/conf/httpd.conf, you would run

grep -i user /etc/httpd/conf/httpd.conf

(-i makes the search case-insensitive).

Normally grep does not tell you the line number where it finds the term. If you want to find out the line number, run

grep -n -i user /etc/httpd/conf/httpd.conf

You can find out about logged in users either by running

who

(Sample output:

server:~# who
root     pts/0        Nov 12 11:28 (192.168.0.202)

)

or

w

which gives more detailed output:

server:~# w
 11:29:49 up  2:19,  1 user,  load average: 0.02, 0.01, 0.00
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
root     pts/0    192.168.0.202    11:28    0.00s  0.08s  0.01s w

To edit files on the command line, you can use an editor such as vi. To open the file, run

vi /path/to/file

Now you see the contents of the file (if there is any. Please note that the file is created if it does not exist yet.).

The most important commands in vi are these:

Press i to enter the Insert mode. Now you can type in your text.

To leave the Insert mode press ESC.