Tuesday, August 31, 2010

Episode #110: Insert Title Here

In this corner, Tim, the disputed PowerShell Heavyweight Champion of the World:

What is in a title? Titles are important and they can be really useful. An aptly named window can be useful for screen shots, managing multiple sessions, and for basic organization. The default PowerShell title of Administrator: C:\WINDOWS\system32\WindowsPowerShell\v1.0\powershell.exe can be really useless. So how do we rename the window to something more useful?

PS C:\> (Get-Host).UI.RawUI.WindowTitle = "Shell to Take over the World"
Boom! Now we have a window that is distinct from our other windows, and clearly displays its use for world domination. So how does the command work?

Get-Host returns an object that represents the host. By accessing the UI, RawUI, and WindowTitle property hierarchy we can modify the title. Not straight-forward, but rather simple. As for the actual plans to take over the world, those aren't simple, nor are they for sale.

And in the red trunks, Hal is undisputedly heavy

Oh sure, namby-pamby Powershell can have an elegant API for changing the window title, but in Unix we prefer things a little more raw:

$ echo -e "\e]0;im in ur windoz, changin ur titlz\a"

Yep, that's the highly intuitive sequence "<Esc>-right bracket-zero-semicolon-<title>-<BEL>" to set your window title to "<title>". Since this obviously doesn't roll trippingly off the fingers, I generally create the following shell function in my .bashrc:

function ct { echo -e "\e]0;$*\a"; }

See the "$*" in the middle of all the line noise? That takes all of the "arguments" to the function (anything we type on the command line after the function name, "ct") and uses them as the title for your window. So now you can change titles in your windows by typing:

$ ct im in ur windoz, changin ur titlz

And that's a whole lot nicer.

Another cool place to use this escape sequence is in your shell prompt. Yes, I know we've done several Episodes at this point that deal with wacky shell prompt games, but this is a fun hack:

$ export PS1='\e]0;\u@\h: $PWD\a\h\$ '

Here we've embedded our title-setting escape sequence into the PS1 variable that sets up our command-line prompt. We're using it to set the window title to "\u@\h: $PWD", where \u is expanded by the shell as our username, \h is the unqualified hostname, and $PWD is our current working directory. So now we can easily look at the window titles and know exactly who and where we are. This is useful for picking out the one window we want if we have a stack of minimized terminal windows. Notice we also have "\h\$ " after the escape sequence which will actually set the visible shell prompt we see in our terminal window.


Mike Cardosa slips something a little extra into his gloves, cmd.exe

Only a true Unix guy would use the word "elegant" to describe the PowerShell method for setting the window title. I do not think that word means what you think that it means.

It turns out that the cmd.exe developers failed to achieve the level of obscurity that we've come to expect when dealing with this humble shell.

Ladies and gentlemen, introducing quite possibly the most intuitive command available in cmd.exe:

C:\> title h@xor at work
That's it! We've managed to change the window title using the simple 'title' command. Just feed it any string you'd like and you are good to go. Including environment variables is also startlingly simple:

C:\> title netcat listener on %computername%
Look at that. The window title - including environment variable - is set without using a single cryptic command line switch or for loop.

Fortunately for sys admins (and certain bloggers), this sort of simplicity is the exception rather than the rule, so the world still needs those with a mastery of obscure commands.