Walking Up Directories For Every ..

FossilizedDaemon · 06-09-2024, 10:35 PM

Hello,

I am currently trying to implement a basic shell function that will

Code:

cd ../

for every .. I type into the shell. This is actually being aped from magicdots for zsh. I know the underlying logic, but am mainly running into trouble with actually interfacing with the shell itself. I do not know if that makes sense, so I will just get the code in hopes it helps other understand. Currently I have the following function.

Code:

_walk() {
	case "${1}" in
		..*)
			i=0
			directories_to_walk=$(printf "%s" "${1}" | tr -d '/' | grep -o '..' | wc -l)

			while [ "${i}" != "${directories_to_walk}" ];
			do
				if [ $(pwd) = '/' ]; then
					return;
				fi

				cd ../
				i=$((i+1))
			done
			;;
	esac
}

This runs perfectly, and in fact is POSIX compliant so you can use it in any POSIX shell, there is one issue I can't fix however. I do not want to have to type

Code:

walk ../../

I just want to be able to type

Code:

../../

I know being able to do this will depend on the shell (I am using yash), but I cannot find how to set this for the life of me. Does anybody know?

NevemTeve · 06-09-2024, 11:01 PM

As a start:

Code:

- while [ i != "${directories_to_walk}" ];
+ while [ x"$i" != x"$directories_to_walk" ];

FossilizedDaemon · 06-09-2024, 11:15 PM

Quote:

Originally Posted by NevemTeve

As a start:

Code:

- while [ i != "${directories_to_walk}" ];
+ while [ x"$i" != x"$directories_to_walk" ];

While I understand what the removal of the braces does I do not understand what the x does.

NevemTeve · 06-10-2024, 01:30 AM

Some versions of test(1) might get confused if your variables contain unusual values like '', '-a', '!=' etc; prepending an 'x' solves this. Nonetheless the important point here is using "$i" instead of i

pan64 · 06-10-2024, 02:14 AM

I don't really understand, a simple cd $1 would do the job I think, without while, grep and whatnot.
That code is extremely inefficient, running that directories_to_walk= line for every directory is terrible. But anyway, if it works you can use it.

FossilizedDaemon · 06-10-2024, 09:23 AM

Quote:

Originally Posted by pan64

I don't really understand, a simple cd $1 would do the job I think, without while, grep and whatnot.
That code is extremely inefficient, running that directories_to_walk= line for every directory is terrible. But anyway, if it works you can use it.

You could do it that way, but then you would have to adhere to the cd syntax which this lets you avoid doing for easier spamming when you want to walk back a lot. I won't say it's a good habit to form, but it's one I have and this is the solution to it.

FossilizedDaemon · 06-10-2024, 09:24 AM

Quote:

Originally Posted by NevemTeve

Some versions of test(1) might get confused if your variables contain unusual values like '', '-a', '!=' etc; prepending an 'x' solves this. Nonetheless the important point here is using "$i" instead of i

Gotcha.

pan64 · 06-10-2024, 09:31 AM

Quote:

Originally Posted by FossilizedDaemon

You could do it that way, but then you would have to adhere to the cd syntax which this lets you avoid doing for easier spamming when you want to walk back a lot. I won't say it's a good habit to form, but it's one I have and this is the solution to it.

I don't understand it. Can you show some examples?

boughtonp · 06-10-2024, 10:32 AM

This is a dubious idea to start with, but that implementation is stupidly over-convoluted.

Since Yash claims to have command-not-found functionality, read its documentation to discover how that functions and then all it should take is simple logic equivalent to...

Code:

if "$MISSING_COMMAND" matches '^(\.\./)+$' then cd "$MISSING_COMMAND"

As for that "x" stuff, you can safely ignore it - it is NOT needed for POSIX-compliant shells, which Yash claims to be. (It was a workaround for bugs in old shells.)

FossilizedDaemon · 06-10-2024, 11:22 AM

Quote:

Originally Posted by boughtonp

This is a dubious idea to start with, but that implementation is stupidly over-convoluted.

Since Yash claims to have command-not-found functionality, read its documentation to discover how that functions and then all it should take is simple logic equivalent to...

Code:

if "$MISSING_COMMAND" matches '^(\.\./)+$' then cd "$MISSING_COMMAND"

As for that "x" stuff, you can safely ignore it - it is NOT needed for POSIX-compliant shells, which Yash claims to be. (It was a workaround for bugs in old shells.)

I have been reading over their documentation and added the command-not-found part, but keep running into issues where when I give ../ or .. it says command-not-found or this is a directory and does nothing. My Yash specific code looks like this

Code:

_walk() {
	case "${1}" in
		..*)
			i=0
			directories_to_walk=$(printf "%s" "${1}" | tr -d '/' | grep -o '..' | wc -l)

			while [ "${i}" != "${directories_to_walk}" ];
			do
				if [ "$(pwd)" = '/' ]; then
					return;
				else
					cd ../
					i=$((i+1))
				fi
			done
			HANDLED=true
			;;
	esac
}
COMMAND_NOT_FOUND_HANDLER=("${COMMAND_NOT_FOUND_HANDLER}" '_walk "${@}"')

As for the logic you gave, it wouldn't work exactly how I like this to work (i.e. where '..', '../', '.......', '../.../.../...../' all are valid ways of using it). The documentation you linked on the 'x' stuff is very interesting, thank you! I had no idea older shells needed that work around.

EDIT:
Aha! It was an issue somewhere else in my configuration. I got it to work now, thank you

pan64 · 06-10-2024, 11:29 AM

That is still utterly overcomplicated
remove every './' from the input string, count the remaining number of dots and cd .. that many times. And do nothing if there are other chars inside.
checking / is not really required, because .. is defined in the root dir too.

FossilizedDaemon · 06-10-2024, 12:37 PM

Quote:

Originally Posted by pan64

That is still utterly overcomplicated
remove every './' from the input string, count the remaining number of dots and cd .. that many times. And do nothing if there are other chars inside.
checking / is not really required, because .. is defined in the root dir too.

While I would love to improve my code, I am a little confused here. From my understanding I am counting how dots there and cding that many times. Do you mean outside of a loop? I don't really know how I would do that, don't I need something to keep track of how many times I have already cded? As for the '/' check, I do this because otherwise my AUTO_AFTER_CD stuff will get run even when it cd ../ in root and I will get a bunch of ls output for root.

pan64 · 06-10-2024, 01:57 PM

Code:

_walk() {
    waste=$(printf "%s" "${1}" | sed 's#[./]*##g')  # if it is not empty there is something "else" in $1
    dots=$(printf "%s" "${1}" | sed 's#\./##g')     # just remove every ./ (what to do if we have // in it?) - sed s!//*!/!g will remove it
    for (number of . in dots -1)                    # which is the length of dots -1  (but you can add / to the initial string, in that case -1 is not needed)
      cd ..
}

I meant something like this. But it is not tested.

FossilizedDaemon · 06-10-2024, 02:41 PM

Quote:

Originally Posted by pan64

Code:

_walk() {
    waste=$(printf "%s" "${1}" | sed 's#[./]*##g')  # if it is not empty there is something "else" in $1
    dots=$(printf "%s" "${1}" | sed 's#\./##g')     # just remove every ./ (what to do if we have // in it?) - sed s!//*!/!g will remove it
    for (number of . in dots -1)                    # which is the length of dots -1  (but you can add / to the initial string, in that case -1 is not needed)
      cd ..
}

I meant something like this. But it is not tested.

Ahhh, this is the difference. The for loop arithmetic method is not POSIX compliant so it wouldn't work for me. The sed statement is useful, but aside from that this wouldn't work for me. Thank you though

pan64 · 06-11-2024, 12:31 AM

obviously you need to make it work for yourself if you wish. It is not a for loop but a pseudo code which is only used to explain the algorithm. Or probably better to say, it is just an idea.