Do shell script problem in Applescript

Question

Hi,
I am an Applescript novice and have been trying to write a code to go to a particular folder, look for all files in the folder tree with extension .m2v and run an executable file to decode them. My problem is that when I run my code (containing do shell script), it searches through all files and folders on Mac HD and starts decoding .m2v files elsewhere that I don't want.
Eventually it runs out of space (.m2v file decoding takes a lot of space), because it is dumping all decoded .yuv files onto the HD.
When I run the command on Terminal, it executes the decoding perfectly and stores the decoded files in the same folder.
Please help me about what's going on.
My code is something like:
tell application "Finder"
set DestinationFolder to "xxxxxx:xxxx:xxxx"
set NumFolders to (get count of folders under Destination folder)
repeat for SomeVar from 1 to NumFolders
set FolderinQuestion to folder SomeVar of DestinationFolder
-- Tried tell application "Terminal" here, but did not know --how to export the FolderinQuestion variable from Finder to --Terminal
do shell script " \" cd \" & (POSIX path of (result as text));
for file in `find $pwd \"*.mov\"`
do
/usr/local/bin/decode file
done"
end repeat
end tell
I would greatly appreciate some guidance.

Answer 1

The root of the problem is that you're trying to quote the cd command for some reason:
<pre class=command>do shell script " \" cd \" & (POSIX path of (result as text));
...</pre>
In addition to that you're including the & (POSIX path of (result as text)) as part of the shell command whereas this should be OUTSIDE of the quotes in order to get evaluated
If you work that through you'll end up with a shell command that looks like:
<pre class=command>" cd " & (POSIX path of (result as text))</pre>
If you try to run that in a terminal you'll get a cd : command not found error and that's why the rest of it appears to fail.
The solution to that one is simple - just don't bother quoting the cd and put the POSIX path stuff outside of the quotes to get it evaluated at runtime:
<pre class=command>do shell script "cd " & quoted form of POSIX path of (FolderInQuestion as text)) & ";
# rest of shell commands here"</pre>
Now, as for the rest of the script there are a few things I would change.
First, unless you need to know the index, don't do:
>repeat for SomeVar from 1 to NumFolders
set FolderinQuestion to folder SomeVar of DestinationFolder
the issue is that the number of folders to process may change during the script's execution (other processes may create or remove folders). This will, at best, cause some folders to be skipped and, at worst, cause the script to fail.
If you're iterating through a list, the best option is to just:
<pre class=command>repeat with FolderInQuestion in (folders of DestinationFolder)
...</pre>
This automatically sets the iterator (in this case, FolderInQuestion, to the first item in the list and increments it for each iteration through the loop.
Secondly, in your shell script itself, scrub the entire do/done loop. You're already using find, so have that do the hard work using the -exec switch:
<pre class=command>find path -name "*.mov" -exec /usr/local/bin/decode {} \;</pre>
In find's case, {} is substituted with the current file's path.
Putting this together you'd get:
<pre class=command>tell application "Finder"
set DestinationFolder to "xxxxxx:xxxx:xxxx"
repeat with folderInQuestion in (get folders of folder DestinationFolder)
do shell script "cd " & quoted form of POSIX path of folderInQuestion & "; find . -name \"*.mov\" -exec /usr/bin/decode {} \\;"
end repeat
end tell</pre>
Note that I've used 'quoted form of POSIX path' - this takes care of any shell-unsafe characters like spaces in the path name. I've also used \\; for the -exec switch - this is so that AppleScript passes the \ to the shell command rather than using it for its own escaping.
But you're not done yet!
There's still one fatal flaw in this process - and that is the fact that find by default, is recursive - it will walk through every directory that it finds.
This means that if you start at the top folder and iterate through, find will find all .mov files and decode them. Your script then cd's to the first subdirectory and repeats the process - decoding all the .mov files in that directory and all its subdirectories even though they've ALREADY been decoded.
The upshot is that you only need to run one loop starting at the top level. You don't need to iterate through all the subdirectories since find will do that for you.
In addition to that, there might not be a need to use cd at all since the first argument to find is the directory to start searching in. Unless there's some reason that you need to start decode from the top level directory (e.g. is that where it saves the files?), you can drop the whole repeat loop altogether and just run with:
<pre class=command>set startFolder to (choose folder)
do shell script "find " & quoted form of posix path of startFolder & " -name \"*.mov\" -exec /usr/bin/decode {} \\;"</pre>
That's the entire script - a radical compression of your original.