[SOLVED] Can variables be used in multiple directory {f1,f2,...,N} syntax?

andrew.comly · 01-19-2016, 02:49 AM

Can variables be used with the multiple directory {folder1,folder2,...,folder N} syntax?

I would like to check how many total files are in four specific sub-directories of the ~/.config/cairo-dock directory. I successfully find out how many by the command:

Code:

$ find ~/.config/cairo-dock/{current_theme,stack,themes,third-party} -type f | wc -l
829

I would like to use a variable to replace the {folder1,folder2,...,folder N} syntax. E.g.

Code:

DIR=current_theme,stack,themes,third-party

and then

Code:

$ find ~/.config/cairo-dock/{${DIR}} -type f | wc -l

Unfortunately this results in

Code:

find: `/home/a/.config/cairo-dock/{current_theme,stack,themes,third-party}': No such file or directory

Whenever the ${DIR} is used and not the longhand {current_theme,stack,themes,third-party} it doesn't work.

Using variables would be more convenient in a script where the {current_theme,stack,themes,third-party} is repeated.

Some attempts are below:

ATTEMPTS
I first set the variable:

Code:

DIR=current_theme,stack,themes,third-party

Next , I check that this variable will display correct text:

Code:

$ echo "/home/a/.config/cairo-dock/{${DIR}}"
/home/a/.config/cairo-dock/{current_theme,stack,themes,third-party}

I then try to count the number of files by either find or ls:

Code:

$ find $(echo "/home/a/.config/cairo-dock/{$(echo "${DIR}")}") -type f
$ ls -d $(echo "/home/a/.config/cairo-dock/{$(echo "${DIR}")}")
$ find $(echo "/home/a/.config/cairo-dock/{$(echo "$DIR")}") -type f
$ ls -d $(echo "/home/a/.config/cairo-dock/{$(echo "$DIR")}")
$ ls -d /home/a/.config/cairo-dock/{$(echo "$DIR")}
$ ls -d /home/a/.config/cairo-dock/{$(echo `$DIR`)}
$ ls -d /home/a/.config/cairo-dock/{$DIR}
$ ls -d /home/a/.config/cairo-dock/{$(echo `$DIR}`)
$ ls -d /home/a/.config/cairo-dock/{$DIR}
$ ls -d $(echo "/home/a/.config/cairo-dock/{$DIR}")

All of the above attempts result in one of the following errors:

Code:

ls: cannot access /home/a/.config/cairo-dock/{current_theme,stack,themes,third-party}: No such file or directory

OR

Code:

find: `/home/a/.config/cairo-dock/{current_theme,stack,themes,third-party}': No such file or directory

SAbhi · 01-19-2016, 03:27 AM

well if its just to find teh no of files in sub directories, i would say the approach doesn't looks good, you are using find where you already know the location of files :

A simple code for your requirement though it would not be the compact of all which can be achieved.

Code:

for i in /home/a/.config/cairo-dock/; do echo -e "$i:\c ";ls $i|wc -l; done

andrew.comly · 01-20-2016, 04:45 AM

Quote:

Originally Posted by SAbhi

A simple code for your requirement though it would not be the compact of all which can be achieved.

Code:

for i in /home/a/.config/cairo-dock/; do echo -e "$i:\c ";ls $i|wc -l; done

Yes, I guess I am too curious for learning a quicker way.

I can just first Define the variable FLDRS:

Code:

FLDRS="/home/a/.config/cairo-dock/current_theme /home/a/.config/cairo-dock/stack /home/a/.config/cairo-dock/themes /home/a/.config/cairo-dock/third-party"

and use a simple "for $i in `echo "$FLDRS"`; do ... done" loop like above.

Curiosity is good but excessive curiosity can cause one to waste time chasing after illusions. Often times the simplest way is the best.

SAbhi · 01-21-2016, 10:12 AM

Quote:

Originally Posted by andrew.comly

Yes, I guess I am too curious for learning a quicker way.

I can just first Define the variable FLDRS:

Code:

FLDRS="/home/a/.config/cairo-dock/current_theme /home/a/.config/cairo-dock/stack /home/a/.config/cairo-dock/themes /home/a/.config/cairo-dock/third-party"

and use a simple "for $i in `echo "$FLDRS"`; do ... done" loop like above.

Curiosity is good but excessive curiosity can cause one to waste time chasing after illusions. Often times the simplest way is the best.

well using `echo $FLDRS` is again a useless use inside for when only $FLDRS can give you what you need.

andrew.comly · 01-22-2016, 11:52 PM

Answered!

(But on another thread)

To those of us who hold safety as a top priority, due to bash's order of expansion using variables inside brackets simply is not an efficient practice. Please peruse the answer below from http://www.linuxquestions.org/questi...rs-4175563266/.

Quote:

Originally Posted by rknichols

The relevant paragraph from the bash manpage is under EXPANSION:

The order of expansions is: brace expansion, tilde expansion, parameter, variable and arithmetic expansion and command substitution (done in a left-to-right fashion), word splitting, and pathname expansion.

Brace expansion is performed before variable expansion, so "{${ALPHA}}" isn't seen as a legitimate brace expansion (there's no comma inside those braces) and is left as-is. (The output from "-x" puts quotes around it since it contains characters that are special to the shell.)

You can force the expression to be re-parsed after variable expansion by using eval, but that is extremely dangerous unless you have absolute confidence that the string being passed to eval can't contain anything dangerous like content from an outside source, since that could include things like command substitution running arbitrary commands. If you are sure that the content of ALPHA is always safe, then

Code:

eval mkdir -p 1 {${ALPHA}}

No Sir, I'm not forcing anything!!

Safety prevents mishaps. Preventive maintenance saves time in the long run.