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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). Othe
by 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 agoWe 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 agoAnd 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 agoThe 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 agoAs 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 agoI'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.
- remram 4y agoThat sounds like a weird way to implement a built-in command (the IPC handler still needs to be built-in, so you didn't really remove it from the shell). And then if course that binary would be available globally but only work if you're using the shell it's built for...
- daptaq 4y agoYeah, that is why it isn't done. I am just pointing out the pointless fact that you could write a cd command that wasn't itself built-in.
- remram 4y agoYou could hook up to the parent process with ptrace or the equivalent debugging API of your OS of choice and forcibly change the directory. Stackoverflow even has an implementation: https://unix.stackexchange.com/a/114262/81005 https://unix.stackexchange.com/a/114262/81005
- 0x445442 4y agoDon’t forget “dirs -v”. I’ve tried to use Powershell a few times and always tap out because it doesn’t come with the dirs command. It’s so fundamental to my workflow a shell without it or without an easy way to implement it is a no go.
- yewenjie 4y agoI'm curious if this is true for every alternative new niche shells like murex, oil, nushell etc?