4 ms·

Something to note which wasn't mentioned here is that `cd` is not a binary executable, but instead a shell command. You won't find it anywhere in /bin, /sbin an

Something to note which wasn't mentioned here is that `cd` is not a binary executable, but instead a shell command. You won't find it anywhere in /bin, /sbin and so on. That's also why `sudo cd ` doesn't work, `sudo` will try to execute `cd` as root but it's not an executable so it won't find it. (tip: do `sudo -i` instead)

saagarjha 4y ago
Many platforms will ship a (mostly) useless cd binary.
rjsw 4y ago
An executable of 'cd' wouldn't do anything useful, it could only change its own idea of working directory then exit, the shell or other executable that invoked it would be unchanged.
- stjohnswarts 4y ago
  why couldn't it call an api in the shell to change directory?
  - remram 4y ago
    What would that improve? And what happens if you call it from another shell?
    - stjohnswarts 4y ago
      I never implied that it was better or worse but that it was possible
remram 4y ago
cd is a good example of something that has to be a built-in command, because it makes the shell itself do something (change its current working directory). Other commands in that category are umask, the job control ones (fg, bg, wait, ...), the ones setting variables (read, printf), and the control flow ones (if, while, break, return, exit, ...). A lot of commands are also built-in for convenience but don't strictly need to be.
- nixcraft 4y ago
  We can use the `compgen -b` (`help cd` to get short help or `man bash-builtins` to read man pages) to list all internal bash commands. For example, we can use the `type -a cmd1` or `command -V cmd1` to see if `cmd1` is built-in or external binary.
- emmelaich 4y ago
  And yet ... https://unix.stackexchange.com/questions/50058/what-is-the-point-of-the-cd-external-command https://unix.stackexchange.com/questions/50058/what-is-the-p... Yes, it's idiotic.
  - version_five 4y ago
    The question and highest rated reply there are very interesting and worth reading (at least for trivia value), thanks for that. I don't understand what you meant is idiotic though
    - ianai 4y ago
      As that comment said, it’s there so utilities can use it for checking the return of “chdir()”. It’s at best a name conflict with a shell command with a well established past and use. At worst, it probably enables some bad code smells or outright malicious code.
    - emmelaich 4y ago
      I've seen questions about sudo (for instance) that ask why does "sudo chdir" not work. By idiotic I think it's a mistake to blur the line between shell builtins and external commands.
- daptaq 4y ago
  > cd is a good example of something that has to be a built-in command Theoretically you could also have a cd that would IPC the shell to change the pwd but I guess you could also say that is overengineering.

saagarjha 4y ago

Many platforms will ship a (mostly) useless cd binary.

rjsw 4y ago

An executable of 'cd' wouldn't do anything useful, it could only change its own idea of working directory then exit, the shell or other executable that invoked it would be unchanged.

stjohnswarts 4y ago
why couldn't it call an api in the shell to change directory?
- remram 4y ago
  What would that improve? And what happens if you call it from another shell?
  - stjohnswarts 4y ago
    I never implied that it was better or worse but that it was possible

remram 4y ago

cd is a good example of something that has to be a built-in command, because it makes the shell itself do something (change its current working directory). Other commands in that category are umask, the job control ones (fg, bg, wait, ...), the ones setting variables (read, printf), and the control flow ones (if, while, break, return, exit, ...). A lot of commands are also built-in for convenience but don't strictly need to be.

nixcraft 4y ago
We can use the `compgen -b` (`help cd` to get short help or `man bash-builtins` to read man pages) to list all internal bash commands. For example, we can use the `type -a cmd1` or `command -V cmd1` to see if `cmd1` is built-in or external binary.
emmelaich 4y ago
And yet ... https://unix.stackexchange.com/questions/50058/what-is-the-point-of-the-cd-external-command https://unix.stackexchange.com/questions/50058/what-is-the-p... Yes, it's idiotic.
- version_five 4y ago
  The question and highest rated reply there are very interesting and worth reading (at least for trivia value), thanks for that. I don't understand what you meant is idiotic though
  - ianai 4y ago
    As that comment said, it’s there so utilities can use it for checking the return of “chdir()”. It’s at best a name conflict with a shell command with a well established past and use. At worst, it probably enables some bad code smells or outright malicious code.
  - emmelaich 4y ago
    I've seen questions about sudo (for instance) that ask why does "sudo chdir" not work. By idiotic I think it's a mistake to blur the line between shell builtins and external commands.
daptaq 4y ago
> cd is a good example of something that has to be a built-in command Theoretically you could also have a cd that would IPC the shell to change the pwd but I guess you could also say that is overengineering.