Example

kill -9 2342

If you type top again you should see that the process that was associated with that PID is no longer running.

Below, you will see all the processes that are running on your computer. It gives most of the info about the processes that you will ever need to know. The main columns I focus on are PID, USER, %CPU, and %MEM. They are to me the most useful. PID is the process ID which is very useful when a program freezes. USER is who is running the program. %CPU is the amount of processing power the program is using. %MEM IS the amount of memory the program is taking up.

Top by itself only gives you information on what is running, but when you combine it with other commands, it makes it very powerful. We will get into that next time.

Example:

locate report

You can also search for all files with a certain extension.

Example:

locate '*.jpg'

You may be saying why would I want to do such a specific search? Well lets say you are a web designer that need to modify a template file for all your websites that contain a certain function. Say the function was called capcha and all your template files end in .tpl. You would use you the | command to combine the two function together to accomplish this.

Example:

locate '*.tpl' | grep -R 'capcha' *

This works by running the locate command and then using grep on just the file names that locate returns. Yes you could just type grep -R 'capcha' *, but you would have to be in the root directory of your hard drive and the grep command would search every file on our computer. That would take a long time to complete, and if you are running the search on a web server you could bring it to its knees.

The basic structure of a grep statement is below.

grep -R "string you are looking for" *

The -R in the statement means you want to search recursively. Make sure you put the “” around your string or you will get an error when you try to execute the command. The * means that the preceding item will be matched zero or more times.

Their are many more options that can be added into the grep function to make it even more useful. To find them type the following into the command line.

man grep

For example, suppose you have a text file full of email addresses, with one email address per line. Suppose it’s named “emails.txt” and it’s on your Desktop.

To view the emails, type the following command in the Terminal:
cat ~/Desktop/emails.txt

To view the emails sorted alphabetically, type the following:
cat ~/Desktop/emails.txt | sort

The pipe causes the output of the cat command to be fed into the sort command, then outputted to the screen. You can tack on as many pipe commands as you need.

To view the emails sorted alphabetically and with a prompt between each page, type:
cat ~/Desktop/emails.txt | sort | more

The list of emails “flows” from the cat command to the sort command to the more command, as if going through water pipes.

The first category of Unix commands for working with text files might be called “text viewers”. These includes commands such as cat, head, tail, more, and less. All of these commands are used by typing the command plus the name of a file.

cat — Short for “concatenate”, this command is used to temporarily combine files. But if you use it on only one file, it just displays the file to the screen.

head — This command shows the first 10 lines of a file. (You can adjust the number of lines using the flag -n.)

tail — This command shows the last 10 lines of a file. (You can also use -n here to show more lines.)

more — Like cat, this shows the entire contents of a file, but prompts you for “more?” between each page. Hit the space bar to go to the next page, or use the up and down arrows. Hit “q” to quit.

less — This is another “pager” like more, i.e. it shows one page at a time. It was meant to be a successor or alternative to more and was hence given the opposite name less. It had more features than more (sounds like an Abbott and Costello routine) when it first came out, but now the two commands are about the same.

Here are some examples:

How to view your hosts file, where you can map host names to IP addresses:
cat /etc/hosts

If you have Personal Web Sharing turned on, how to view the last 10 lines of the Apache log file:
tail /var/log/httpd/access_log

How to read the Apache configuration file, one page at a time:
more /etc/httpd/httpd.conf

The dot is useful for hiding configuration files that might otherwise clutter your view. On a web server like Apache, files beginning with a dot can’t be accessed over the web. That’s why you can safely put configuration options for each directory in an .htaccess file. (If you have a web site, you’ve almost certainly seen .htaccess files.)

In addition to the Unix method of hiding files by beginning them with a dot, Mac OS X also includes its own unique way of hiding files and folders. If you install the Developer Tools CD that came with your Mac, you’ll have access to a SetFile command. You can type SetFile -aV and the name of a file to make the file invisible. You can use SetFile -av (lowercase “v”) to make the file visible again.

In addition, you can see ALL the files on a computer by using Applications like Smultron that have an “Open Hidden” option.

If you want to simply rerun the last command, you can type !!.

You can also scroll through the command history by pressing the Up and Down arrows at a blank prompt. As soon as you find a command you want to rerun, you can edit it as needed or simply press Enter.

In your home folder you’ll find a file called .profile that contains settings for working in the bash shell (which is what you do every time you use Terminal.) It’s sort of the “preferences” file for the command line. The .profile file can do a lot of things, one of which is making tab completion case-insensitive. (We’ll cover more uses of .profile later.)

Because .profile begins with a dot, it’s invisible to most Mac OS X applications. A notable exception is Smultron, a free text editor that has an “Open Hidden” option. You can either use Smultron to open .profile in your home folder, or open Terminal and type open .profile, which should open the file in Apple’s TextEdit. If you don’t have this file, you’ll just create a new empty file by the same name and save it.

The line you’ll add to .profile is the following:

bind "set completion-ignore-case on"

If your .profile contains other text, simply put this at the end on its own line. If you’re creating .profile from scratch, this is the only line you’ll need. Save and close .profile.

After closing and reopening Terminal, your tab completion should now be case-insensitive. If you type cd doc and hit tab, it should fill in cd Documents/.

You’ll also notice that tab completion only works when whatever you’re typing is unique. (Or rather, it only works to the degree that it is unique.) For example, if you type cd D from your home directory and hit tab, Unix won’t fill in anything because it doesn’t know whether you want cd Desktop or cd Documents. But if you hit tab a 2nd time, it will display Desktop and Documents to show you your options. Hitting tab once always causes Unix to fill in as much as it can. Hitting tab the 2nd time always shows you your options, if any.

You can even use tab completion to select a command. At the beginning of a command prompt, hitting tab twice will cause Unix to display ALL the commands that are available to you. There will probably be so many that Unix will ask you if you really want to see them all. Hit “y” to confirm, and then hit “q” (quit) when you’re done.

Tab completion makes it much easier to work with Unix.