Table of Contents

1. Why this post
2. Before we begin | BASIC GOOD TO KNOW
   1. Readline
   2. ZLE
3. Making of our custom widget
4. My words to you dear friend
5. Refrences

Why this post

I was always wondering why many of emacs keybindings work in terminal. Being dependent on key combinations ctrl+e, ctrl+a, alt+t, ctrl+t (my favorite)… every time i am fooling around the terminal, it felt so bad👿 if someone is navigating around pressing arrow keys ⬅️⬅️⬅️⬅️…so maaaaanyyyy times, swagging them these nifty shortcuts is so fun. Until my friend/binaysakya 👨‍💻 told me you should write about these things. I realized I know nothing what those bindings really meant 🤔 That’s how this post happened.

next candidate post, Alt +w , Ctrl + y, Ctrl +w , Ctrl + K

— मिलन थापा (@thapakazi_) December 14, 2017

I would sharing my learning below more aliened to ZLE. I have copied the lines from the reference links below 🙊🙈🙉

Before we begin | BASIC GOOD TO KNOW

Here we would look good to know theory that this post revolves around, skip🚀 these theory at your risk.

Readline

Its a library used by bash and many of CLI programs to edit/interact via command line. Readline uses Emacs style shortcuts as default, that’s why your Ctrl+a, Ctrl+e… shortcuts works almost same in most of terminals, even the editors derivations like sublime respects🙇 the style. And yes, because of this it super easy to jump along the text interface with such a ease ☺️

ZLE

I have shifted to zsh like few years back, no speical reason still playing back and forth between bash and zsh. Just love the random theme from robbyrussell/oh-my-zsh.😄 till yesterday(22 dec 2017) when I found this thing called zle(ZSH LINE EDITOR) then I was like oh my… its so 😍😍😍

ZLE is a powerful line editor, what that means… ? Every shell provides some kind of editing capability although it could be basic stuffs provided by os like enter character, delete line, delete word. ZLE extends your capability to interact with your shell with custom functions and custom key strokes, with ease(will share it how in section below ⬇️).

Example you want to change some text you just typed in terminal to UPPER Case. What you can do with zle widget is just like in your editor:

• sample demo of both modes please play along with your shell while you are going via this 🗣

  

• VI

  Set your key-maps to vi with bindkey -v, and now you can use your terminal like your vi i :interactive mode and ESC to command line mode

  echo "hello world" [ESC] [b] [b] [gUw] [w] [gUl] [Enter]
  

  [ESC]	: switch to cmd line mode
  [b] [b]	: jump back 2 words
  [gUw]	: where gU: activate to uppercase widget
  	: w: apply to a word forward
  [w]	: jump a word forward
  [gUl]	: apply uppercase to a first char only

• EMACS (default):

  $ echo "hello world" [alt+b] [alt+b] [alt+u] [alt+c] [crtl+j]   
  

  alt+b alt+b:	jump back by 2 words
  alt+u :	UPPERCASE hello
  alt+c :	Uppercase W in world

ZLE in simple words:

• ZLE is a bridge between you and your zsh shell⁰
• ZLE provides a easy interface to extend the capability of zsh with our custom functions a.k.a widgets
• it’s scope is only within interactive shell
• comes with tons of default keybindings, supports both emacs(default),vi ~keymaps~(modes of editing, collection of keystrokes and interaction mode)
• comes with goodies like:
  • where-is which help us quick look about keymaps
  • zle -la : quick list all the widgets
  • I am still learning, i am liking many small things like [alt+x]

Making of our custom widget

Lets write a widget to find the top 5 memory savages on my machine at this moment. you can simply copy paste the following on your running zsh or source it somewhere in your rc file.

• [step1]: To start with lets define a function, that invokes ps with necessary formatting.

  _exec_ps_top_5(){
      echo "top 5 memory saveges on my machine..."
      PS_FORMAT=%mem,pid,ppid,cmd,comm,etime ps -e|sort -r|head -6
  }
  

• [step2]: define a widget

  zle -N _exec_ps_top_5             # define a new widget
  bindkey '^@' _exec_ps_top_5       # bind it to key ctrl+@
  

• [step3]: execute the widget

  • first check if widget is available or not

    zle -la|grep exec_ps
    [alt+x] where-is [enter] _exec_ps[tab]
    # expected output: _exec_ps_top_5 is on "^@"
    

  • that means our widget is ready to use 😄

    Just press [ctrl+@], you will see sth like this:

    top 5 memory saveges on my machine...
    %MEM   PID  PPID CMD                         COMMAND             ELAPSED
     4.1  1223   549 /opt/google/chrome/chrome - chrome                13:32
     3.2   415     1 /opt/google/chrome/chrome   chrome                13:41
     2.1   875   549 /opt/google/chrome/chrome - chrome                13:36
     1.9   618   415 /opt/google/chrome/chrome - chrome                13:37
     1.9  1743   549 /opt/google/chrome/chrome - chrome                13:18
    

    🎉🎉🎉 Congrats, yeah that’s what it feels like 😌

My words to you dear friend

Please go via the reference url below and explore for your self what awesome things we can do with our shell. ZLE is kinda simple&nice, lets make use of it to do tiny stuffs we repeatedly do in our daily like maybe look after logs like tail -f log/*.log, start our docker containers, run our specs, yeah its could be anything, I have so many alias,functions I depend on everyday, now I would have fun binding them to keystores of my choice 😉

Future Notes: maybe I would try write about readline in days to come, still lot to learn 😃

Refrences

• highly recomended: A closer look at the zsh line editor and creating custom widgets
• Chapter 4: The Z-Shell Line Editor
• Arch wiki::ZSH
• Adam’s UNIX shell environment so many goodies to learn from