Change directory to a folder whose name is in regex notation

Question

I'm in a directory that contains many folders like these:

At_5.2000_displacement
At_-6.4000_displacement
At_2nd_-4.3000_displacement
At_2nd_2.2000_displacement

I am writing a bash script that is cd-ing to each of the folders of the type:

At_X.XXXX_displacement

i.e., I would like to

cd At_5.2000_displacement and cd At_-6.4000_displacement folders. This leaves out the folders of the type:

At_2nd_X.XXXX_displacement

My attempts (Edited):

I found the reg-ex that yields the name of the target folders, which is the following:

At_-\?[0-9][.].*displacement

which yields:

At_5.2000_displacement
At_-6.4000_displacement

Now, in the bash script, every time I do:

cd /path_to_the_folders/At_-\?[0-9][.].*displacement

There is no way of accessing each folder, since the error received is:

trial_cding.sh: line 11: cd: /path_to_the_folders/At_-?[0-9][.].*displacement: No such file or directory

How can I make the line cd /path_to_the_folders/At_-\?[0-9][.].*displacement to work ?

---

The implementation of @dawg's answer via the if statement (not using the shortcut), as far as I understood, would be something like:

for pn in *; do

    if [[ ! -d "$pn" && $pn =~ At_[0-9.-]*_displacement ]]
    then
        echo No desired directory found 
    else
         continue

    cd $pn
    pwd
    cd -
    fi
done

However, this returns no results. What am I getting wrong here?

Also, the I am not quite sure how to use parenthesis in cd $pn in order to avoid going back

---

Regarding the [0-9.-] match...

In the end we are looking for positive or negative decimal numbers. In other words, we are looking for any number from (-)0 to (-)9, and followed by a .

This makes me think that [-0-9.] is the most intuitive instruction.

Surprisingly, it happens that the following three also do match:

[0-9.-]
[0-9-.]   
[-.0-9]

Please check https://regex101.com/r/G3fXo5/1, where I show the matches. This makes me think that the matching criteria inside [ ] is quite broad.

So, I f I try [.-0-9] I get no matching results. Why is this happening? What is the rule behind the matching inside [ ] ?

Answer 1

Assuming X can be only a number, you can use extended globbing:

shopt -s extglob nullglob
for folder in At_?(-)[0-9].[0-9][0-9][0-9][0-9]_displacement/; do
    #do stuff here
    echo "$folder"
done

• shopt -s nullglob is to ensure you won't loop if there are no files matching your pattern
• shopt -s extglob enables extended globs
• ?(-) matches zero or one occurrence of -. In extended globs, the modifier comes before (pattern). See: Pattern matching

Advantage of this approach is looping only over the folders you really want. No additional checks needed.

Answer 2

Given:

$ ls -l
total 0
drwxr-xr-x  2 dawg  wheel  68 Jan  4 10:42 At_-6.4000_displacement
drwxr-xr-x  2 dawg  wheel  68 Jan  4 10:42 At_2nd_-4.3000_displacement
drwxr-xr-x  2 dawg  wheel  68 Jan  4 10:42 At_2nd_2.2000_displacement
drwxr-xr-x  2 dawg  wheel  68 Jan  4 10:42 At_5.2000_displacement
-rw-r--r--  1 dawg  wheel   0 Jan  4 10:51 file

You can use a regular Bash glob *, test to see each glob is a directory -d (vs some other OS object) and then test the string with a Bash regex:

for pn in *; do   # You could use At_*_displacement glob to narrow if desired...
    [[ -d "$pn" && $pn =~ At_[0-9.-]*_displacement ]]  || continue
       # ^^                           a directory?
       #        ^^                    and
       #                ^     ^^      match this regex
       #        OR                                     ^   
       # continue (skip) to the next glob pattern in loop     ^^
    # do you Bash thing on this directory...
    # you can cd "$pn" or operate on the directory directly
    # ( use parenthesis for a sub shell and you don't need to cd back )
    echo "$pn"
done    

Prints:

At_-6.4000_displacement
At_5.2000_displacement

You can also use find with appropriate depth qualifiers and a regex:

$ find . -type d -maxdepth 1 -regex '\./At_[0-9.-]*_displacement'
./At_-6.4000_displacement
./At_5.2000_displacement

And then either use exec {} or xargs or feed that output to a Bash while loop.

---

For your last edit, something like this:

for pn in *; do
    if [[ -d "$pn" && $pn =~ At_[0-9.-]*_displacement ]]
    then
        ( # the ( creates a subshell so no need to cd back...
        echo "Found \"$pn\"! Touching it!"
        cd "$pn"   # USE QUOTES!
        # you are now in that sub directory
        touch "dawg was here!"   # create a file in the directory...
        )
        # exit sub shell -- back to the original directory
    else
         echo "\"$pn\" is not what we are looking for..."
    fi
done

Be sure to use "$quotes" around expansions in Bash.

Answer 3

cd cannot change to more than one directory at a time. You need a for loop.

How about this:

for i in `ls | grep "^At_-\?[0-9][.].*displacement$"`; do
    cd $i
    # do what needs to be done
done