Published at: 09:04 am - Friday April 03 2009
I had a strange problem with Putty when connecting to a Linux server that I work on occasionally. At random times, the line I was typing would wrap around on the same line in crazy fashion, overwriting what I had already typed. Aside from being generally annoying, it caused plenty of headaches when trying to enter commands.
The problem would pop up when entering long commands, but it would also sometimes cause the text to wrap after 20 or so characters. I figured something had to be wrong, and sure enough after a bit of reading, I found the culprit.
It seems that at some point I read a tutorial about how to customize the command prompt that offered tips on how to dynamically change the Putty window title as well. That’s all fine and dandy, but the author left out a very important point, and that was how to escape non-printing characters. You see, the problem with my command prompt was that several non-printing characters were being entered on the line as part of the prompt, and the shell could not accurately determine where to wrap the line, when to add a new line, etc.
Here was my existing prompt:
PS1="[\W]\$ \e]2;[\d \t] [\w]\a" |
What this does, according to the author is create a prompt containing the relative path of the directory I am working in (the \W) surrounded by square brackets, and ending with a “$” sign. The path looks like this:
[www]$ if I happen to be working in a directory named www – simple enough.
The second half of the command (the \e]2;[\d \t] [\w]\a) causes the date and time to be displayed in square brackets ([\d \t]) followed by the full path that I am working on ([\w]). The “\e]2;” and the “\a” are just commands that specify the fact that I wanted to change the window title rather than the command prompt.
The problem? Well, since the commands to change the window prompt are considered non-printing characters, the server would “display” them anyways, taking up room on my command line without me knowing it. the simple fix is to surround the second portion of my prompt command with a pair of brackets used for specifying non-printing characters. They are “\[" and "\]“, used to denote the beginning and end of the non-printing characters, respectively.
So, my new command looks like so:
PS1="[\W]\$ \[\e]2;[\d \t] [\w]\a\]" |
Pretty subtle difference, eh? It makes a world of difference however.
So, if you are seeing some weird behavior when connected to a Linux box with Putty or any terminal client for that matter, take a closer look at your command prompt configuration. Added tweaks such as the window title changes I made along with any sort of color changes you might have made to your prompt are likely the culprit.
Over the past few days, I have made some changes to MailBin that fix some lingering bugs as well as enhance performance. Make sure to check the 
