Change directory to a folder whose name is in regex notation - regex

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