taint.org: Justin Mason’s Weblog

UNIX: another useful tip. Bash supports a wide variety of command line editing tricks; you have the usual GUIish editing (backspace, insert new characters, delete, blah blah) through the GNU Readline library, and in addition to that you have the traditional csh-style history expansion (like ‘!!’ to refer to the previous command typed).

The latter are great, but they won’t actually be expanded until you hit Enter and run the command line. That can be inconvenient, resulting in the user being forced to reach for the rodent for some cut’n'paste instead.

Here’s a handy trick — add this line to ~/.inputrc (creating the file if necessary):

Control-x: shell-expand-line

Start a new bash shell. Now, if you type CTRL-X during command line entry, any shell metacharacters will be expanded on the current command line. For example:

% echo Hello world
Hello world

% echo Hi !$       (press CTRL-X)
           (current command line expands to:)
% echo Hi world

There’s a few more commands supported, but none of them are really quite as useful as shell-expand-line.

Update: ‘Smylers’ wrote to point me at this UKUUG talk from 2003 which discusses .inputrc expansions, and provides some insanely useful tips.

In particular, Magic Space clearly knocks this tip into a cocked hat, by performing the expansion on the fly as you type the command, with no additional keypresses — amazing! Bonus: it works if you use Emacs-mode line editing as well as Vi-mode.

I strongly recommend reading that paper — lots of other good tips there.

Tags: bash, blah, command, editing, expansion, inputrc, line, shell, type, unix, world

Code: Here’s something I came up with recently — it’s actually an evolution of the idea of pushd and popd, as included in BASH. To quote the POD docs:

cdhistory is a perl script used to implement web-browser style “history” for UNIX shells; as you use the cd command to explore the filesystem, your moves are remembered, and you can go “back” through history, and “forward” again, as you like.

Download the perl script here.

Tags: bash, code, evolution, history, idea, perl, pod, popd, pushd, script, something

UNIX: I’ve just made the first change to my core bash configuration in years, to add -b to the set command-line. It triggered some thinking about when the last one was.

It turns out, that apart from writing scripts and aliases frequently, I haven’t changed my commandline UI in any respect, since about 2 years ago. By contrast, I’ve been hacking about with GUI settings continually, new desktop backgrounds, themes, colours, etc. Odd!

Anyway, here’s the tip — it’s very handy, I find.

I changed to using a 2-line prompt, with the first line containing the time and the full working directory, in a ‘magic’ cut-and-pasteable format:

        : exit=0 Thu Jun 24 17:55:29 PDT 2004; cd /home/jm/DL
        : jm 1203...; 

Note that the prompt starts with “:”, which means that bash/sh will ignore the line until it hits “;”. The end result is that the entire line evaluates to “cd /home/jm/DL” when pasted. Hey presto, cd’ing several terminals to the same dir just involves triple-clicking in one, and middle-button-pasting into the others. nifty! Similarly, the second line has a little bit of prompt, but that snippet will be ignored when cut and pasted.

Having the exit status of the last command (bash var: $?) is useful too. The code:

  do_prompt () {
    echo ": exit=$? `date`; cd $PWD"
  }
  PROMPT_COMMAND='do_prompt $?'   # executed before every prompt
  do_prompt 0                     # set up first prompt
  PS1=": `whoami` \!"
  PS2="... >>; "            # continuation prompt
  PS1="$PS1...; "

Tags: bash, change, command, commandline, configuration, core, exit, home, line, respect, unix