Shell shortcuts

In Bash and zsh, you can access the command history by using several shortcuts.  For example, by typing !![Enter], the previous command will be executed.  If you are not sure of what the previous command was, you could do !!:p[Enter] and the previous command will be displayed, but not executed.  Now, if you like what you see, you can do !![Enter], and the shell will execute that command.

Another ! shortcut is !$.   This will give you the end of the previous command.  So if my previous command was:

grep fred /etc/passwd

doing !$ would give me /etc/passwd.  This can be handy.  Say for example the user fred exists on the system, and grep returns his record from /etc/passwd.  If there is something I see in one of the fields that I wish to change, all I need to do (provided that grep was the last command I did) is:

vi !$

This will expand to

vi /etc/passwd

If you are not sure how !$ will expand for you (ie., you cannot remember for certain what your last command was exactly), you can use the :p option:

vi !$:p

Pagers

I won't give you a history of documentation viewers (aka pagers) on *nix systems, other than to say that there used to be pg and more. Then along came less, which was a lot like more, but way better.  Apparently there is a play on words there, so maybe it is true that less is more.

Anyway, I have long followed the advice to use the less pager where it is available.  I don't follow that advice strictly any more.  I now use most. From the most home page:

"MOST is a powerful paging program for Unix, VMS, MSDOS, and win32 systems. Unlike other well-known paging programs most supports multiple windows and can scroll left and right. Why settle for less?"

Indeed.

Making your Bash scripts look a little better

One thing I have noticed about this blog is that shell scripts are _very_ difficult to make look nice.  I am not sure if that is a Blogger problem, or an issue with this template.  Either way, I don't like mucking around with the way things look.  I want to get my ideas down and not have to be constantly tweaking the text formatting.

Anyway, after monkeying around for a while with the shell script on the previous post, I decided to search for a script beautifier, along the lines of GNU indent, but for shell scripts.  Eventually, I came across a ruby script, written by Paul Lutus, and aptly named Bash Script Beautifier.  So far, it has worked very well for me.

As always, utilities such as this one may not work exactly the way you want.  You would do well to make a backup copy of your script before you run it through the beautifier.  Also, be sure to read the documentation on the download page.  You can read all about it, and download the script here.

Optimizing your shell scripts

A few days ago I came across a couple of posts, by Brock Noland, (blog site is dead now) about splitting strings natively with the shell.  You can find them here here (Internet archive) and here here. Basically, the writer demonstrated that using shell builtins and variables is much more desirable than using outside programs, such as cut and awk for the same purpose.  The reason for this is due to speed.  Every time you make a call to an outside program with the shell, you fork a new process, and that takes time.

I decided to tinker with this idea a bit more, to get a better impression of how much slower using cut and awk really is. I made each of the following functions iterate 100 times.  I am pretty sure some of you will be shocked by the speed difference between cut and awk, versus the shell native string splitting.

Using pushd, popd and dirs

Since I have a bit of time on my hands, I thought I might share a trick or two.  Well, not really 'tricks,' but good information to know. I will cover the shell builtins, pushd, popd, and dirs for bash and zsh. Additionally, I will demonstrate how to use some shell aliases, in order to make the use of these handy builtins even more convenient, and time saving.

How to delete the 'Desktop' folder in Gnome...

...and not have the contents of your home directory displayed on your desktop.

Maybe its just me, but I really don't like the way that a fresh Gnome install sets up a user's home directory with a bunch of empty directories, like 'Video', 'Documents', and the totally evil 'Desktop' folder.  If you are like me, you want to decide what is in the home folder, which does not include all the extra directories they offer.  A reasonable person would expect that the quick and easy solution would be to delete the unwanted directories, but not so fast my friend.  All of the directories can be safely deleted, but one.  If you remove the 'Desktop' folder, you will end up with all the contents of your home directory (not including hidden files) displayed on your desktop.   Of course fixing your 'mistake' of deleting the Desktop folder is not as easy as doing a

mkdir ~/Desktop

No no, the wonderful people at Gnome must have thought that would be too easy.  No, first you must search around on the internet and find a post like this one.  Then you have to fire up your editor and do some editing, as well as replacing the folder 'Desktop.'  Then all will be well. Except for the fact that your home directory still has a folder in it that YOU DON'T WANT!!!1!

Anyway, the solution is pretty simple.

ps headers and grep

GNU ps(1) has a plethora of options.  One of the more useful features of ps is the header label which is printed at the top of the ps output, such as in the following snippet:


Listing 1.1
char $ ps
  PID TTY       TIME CMD
15705 pts/1 00:00:00 bash
16345 pts/1 00:00:00 ps


As you can see, each column has a label on the top.  In this example (Listing 1.1), the columns are labelled PID, TTY, TIME and CMD.  This is the most basic invocation of the ps command, and the output is minimal.  If you start adding options, such as doing ps aux, (where you will get you a listing of all the processes on the system using BSD style syntax) you will get quite a bit more text to sift through.  But what if you are only after a certain term, such as tty, for example in the ps aux listing?