Hydra
Edited: Friday 3 October 2025

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Problem

  • I use spacemacs, which is centered around Hydra
  • Over the years I built muscle memory that’s very useful and fast inside Emacs BUT it’s worthless in other applications
  • the next application that I spend most of my time in is the Terminal
  • I would like to make this muscle memory useful in the terminal as much as possible

Finding

  • Bash has a bind command which utilizes readline library key bindings
  • So I can bind a program to space key just like spacemacs
  • Unfortunately, this means pressing space at any time it’ll trigger the program/function
    • To solve this I need it to run only if the line is empty.
    • Pressing space when the terminal is empty doesn’t have any use case for me
    • Then I can bind the space key to shell function that trigger the program only if the line is empty
    • Stackoverflow helped with this

Solution

  • A small program that displays the tree of command similar to Hydra
  • The configuration can be read from a file or more
  • If the user chooses a command the program can execute it
  • Bind space key in the shell to shell function
  • The function checks if the line is empty and runs the command

Issues

  • if I want the command to change the shell’s current working directory it will not work
    • because a process that executes system runs the command in a subshell that exists after the command exists
    • so cd will work inside the subshell and the user’s original shell will have the same original working directory
  • The solution is to
    • Not to execute the command inside the program
    • Print the command and eval it from the shell function
    • Print the UI to stderr instead of stdout to separate the UI output from the command that needs to pass down to the shell to eval it.

Tech stack

  • I wanted an excuse to practice C again and this program seems to be simple enough
  • I used GnuMake to compile and install the program
  • I’m using Bash so anyone with Zsh probably will need to change the shell script

Conclusion

  • It was very useful to develop this program for me to get back to C
  • binding ls to space in Hydra means that I can press space twice in any directory and I’ll get the current directory contents.

References

Backlinks

See Also