how to pass a variable through read in bash

Question

I'm trying to make a script which asks for a directory path and then creates that directory. I'd like to be able to pass variables to the read builtin so pathnames so I don't have to type out full paths:

function make_dir {
echo "What is the path of the directory to be created?"
read directory
mkdir "$directory"
}

so I'd type:

make_dir
What is the path of the directory to be created?
$HOME/temp_dir
mkdir: cannot create directory `$HOME/temp_dir': No such file or directory

So I'd like to have $HOME expanded into /home/user/ and the script to make the directory /home/user/temp_dir, but I can't seem to get the expansion to work.

If I modify the make_dir function to show_dir below

function show_dir {
echo "What is the path of the directory to be created?"
read directory
echo "The directory is $directory"
}

and I type $HOME/temp_dir and get the following:

make_dir
What is the path of the directory to be created?
$HOME/temp_dir
The directory is $HOME/temp_dir

with no expansion. Any ideas on how to get this to work?

Answer 1

It's a little cumbersome, but one option is to use the -e flag to tell read to use Readline to get the input, then use Readline to expand the line after typing it, but before hitting Enter.

$ read -e directory
$HOME/dir

Now type Meta-Control-e, and Readline will expand the input just as if it were being processed prior to execution as a shell command. (Note that the Meta key is probably Alt or Esc, depending on your terminal setup.)

Answer 2

You are actually making things more difficult by attempting to get the directory with read. Unless you have an absolute requirement to use read, you are better off passing the directory to your function as an argument. For example:

function make_dir {
    [ -n "$1" ] || {
        printf "\n usage: make_dir <path_to_create>\n\n"
        return 1
    }
    mkdir -p "$1" || {
        printf "\n error: unable to create '$1', check permissions\n\n"
    }
}

example:

$ function make_dir {
>     [ -n "$1" ] || {
>         printf "\n usage: make_dir <path_to_create>\n\n"
>         return 1
>     }
>     mkdir -p "$1" || {
>         printf "\n error: unable to create '$1', check permissions\n\n"
>     }
> }

$ make_dir $HOME/temp_dir

$ ls -al temp_dir
total 8
drwxr-xr-x  2 david david 4096 Nov 26 15:34 .
drwxr-xr-x 76 david david 4096 Nov 26 15:34 ..

$ make_dir

usage: make_dir <path_to_create>

When you pass the directory to your function as an argument instead of using read, you can easily adjust your function to take/create multiple directories as well:

function make_dir {
    [ -n "$1" ] || {
        printf "\n usage: make_dir <path_to_create> [path2, ..]\n\n"
        return 1
    }
    for i in "$@" ; do
        mkdir -p "$i" || {
            printf "\n error: unable to create '$i', check permissions\n\n"
        }
    done
}

example:

$ make_dir temp_dir_{1..3}
$ ls -1d temp_*
temp_dir_1
temp_dir_2
temp_dir_3

Answer 3

change the following line:

mkdir "$directory"

with

eval mkdir -p "$directory"