How di I enter a sub-shell in a shell-function

Question

Hi Community,
I'm searching for a quick and dirty solution to determine the folder size in a specific location. I tried to do this job in a for-loop but I ran into trouble with folders containing a space in it's name. So I changed the environment variable IFS (Internal Field Separator) to a new-line only instead the default whitespace. But after this I have to leave the shell to get rid of the user-defined IFS variable. Yes I could write the IFS variable in another (auxiliary) variable first to set it back to the default value after running the for-loop but this isn't a quick and dirty solution just for a short look to the folder size in a one line command.
So the one liner looks like:
IFS=$'\n' && for i in `ls`; do du -hs "$i"; done
With the result that the IFS variable changed for this session to a single new line. So I tried to define a shell-function who switch to a sub-shell, set temporary the IFS variable, run the for-loop and exit the sub-shell:
$ foldersize()
> {
> /bin/bash
> IFS=$'\n'
> for i in `ls`; do
> du -hs $i;
> done
> exit
> }
But running the function it only switch to the sub-shell and nothing more happens:
$ foldersize
bash-3.2$
So my question is how can I switch in a sub-shell using in a shell function?
Thx & Bye Tom

Answer 1

What is wrong with
du -hs *
if you want to call it 'foldersize' you can create an alias
alias foldersize='du -hs *'
If you really want to do your loop, you could try something like
foldersize()
    ls -1 "$@" | while read file
    do
        du -hs "$file"
    done
The 'while' loop is running in a sub-shell, so any shell variable changes made in the sub-shell will not be visible when you finish.  For that you could use the following notation:
foldersize()
    while read file
    do
        do -hs "$file"
    done <  <(ls -1 "$@")
Which will run the 'ls' in a sub-process and the 'while' loop will be run in the current shell invocation, and thus any shell variable changes made in the 'while' loop will be available when the loop finishes.
If you just want to do it your way, and do not need any shell variable changes returned to the invoking shell you could use:
foldersize()
    ( IFS=$'\n'
      for i in `ls "$@"`; do
        du -hs $i;
      done
Where everything inside the (...) will be run in a sub-shell, and all variable changes will not show up in the invoking shell.
Then again, you could have just put 'foldersize' in its own script file, made the file executable, and placed the script in $HOME/bin, then added $HOME/bin to your PATH environment variable, and when the script is invoked, it too will run in its own sub-shell.  Simple
#!/usr/bin/env bash
IFS=$'\n'
for i in `ls "$@"`; do
    du -hs $i;
done
The "$@" syntax says if there are any function arguments substute them here and preserve any white space.  The syntax includes the "..." as well as the $@.  All 4 characters need to be specified as "$@" to get the white space preserving effect.  And if there are no function arguments, then it is as if the 'ls' command was specified without additional arguments, as you have used it.  This gives you the ability to get the folder size of the current directory as well as specify any directory you choose.
NOTE:  All of the above should work as shown, most without the need for IFS
Message was edited by: BobHarris