How can I loop through some files in my script? - linux

Question

I am very much a beginner at this and have searched for answers my question but have not found any that I understand how to implement. Any help would be greatly appreciated.
I have a script:
FILE$=`ls ~/Desktop/File_Converted/`
mkdir /tmp/$FILE
mv ~/Desktop/File_Converted/* /tmp/$FILE/
So I can use Applescript to say when a file is dropped into this desktop folder, create a temp directory, move the file there and the do other stuff. I then delete the temp directory. This is fine as far as it goes, but the problem is that if another file is dropped into File_Converted directory before I am doing doing stuff to the file I am currently working with it will change the value of the $FILE variable before the script has completed operating on the current file.
What I'd like to do is use a variable set up where the variable is, say, $FILE1. I check to see if $FILE1 is defined and, if not, use it. If it is defined, then try $FILE2, etc... In the end, when I am done, I want to reclaim the variable so $FILE1 get set back to null again and the next file dropped into the File_Converted folder can use it again.
Any help would be greatly appreciated. I'm new to this so I don't know where to begin.
Thanks!
Dan

Answer 1

Your question is a little difficult to parse, but I think you're not really understanding shell globs or looping constructs. The globs are expanded based on what's there now, not what might be there earlier or later.
DIR=$(mktemp -d)
mv ~/Desktop/File_Converted/* "$DIR"
cd "$DIR"
for file in *; do
: # whatever you want to do to "$file"
done

Answer 2

You don't need a LIFO -- multiple copies of the script run for different events won't have conflict over their variable names. What they will conflict on is shared temporary directories, and you should use mktemp -d to create a temporary directory with a new, unique, and guaranteed-nonconflicting name every time your script is run.
tempdir=$(mktemp -t -d mytemp.XXXXXX)
mv ~/Desktop/File_Converted/* "$tempdir"
cd "$tempdir"
for f in *; do
...whatever...
done

Answer 3

What you describe is a classic race condition, in which it is not clear that one operation will finish before a conflicting operation starts. These are not easy to handle, but you will learn so much about scripting and programming by handling them that it is well worth the effort to do so, even just for learning's sake.
I would recommend that you start by reviewing the lockfile or flock manpage. Try some experiments. It looks as though you probably have the right aptitude for this, for you are asking exactly the right questions.
By the way, I suspect that you want to kill the $ in
FILE$=`ls ~/Desktop/File_Converted/`
Incidentally, #CharlesDuffy correctly observes that "using ls in scripts is indicative of something being done wrong in and of itself. See mywiki.wooledge.org/ParsingLs and mywiki.wooledge.org/BashPitfalls." One suspects that the suggested lockfile exercise will clear up both points, though it will probably take you several hours to work through it.