queries about [:digit:] and cp --verbose effect: GNU shell
I'm new to shell scripting.
I have written the shell below to enable a set of otherwise identically-named .png files to share a single directory.
The script extracts two sample identifiers (numeric) from a parent directory name and adds them to the front of the file.png names which reside in a daughter 'Images' folder.
It all works but ...
1. the commented-out lines for the [:digit:] pattern match do not work (at all). I expected them to to be equivalent to the preceding lines with the less compact  form. What have I missed??
2. despite the fact that the script does what I want, the -v flag gives me verbose messages suggesting otherwise. These occur just after each
scriptname : line number : $f : not found. Which seems odd, since the script does what I want so the file must have been found. The line number is 24, which is the very last line of the script
I'm running Ubuntu 10.04 LTS & Gnome terminal 2.30.2
I have had a good look around this site (and elsewhere) but have been unable to figure out what's wrong. I'd appreciate some help.
So here is the modified code:
Well my first question back is ... which shell? You appear to not define an interpreter at the beginning and the default in Ubuntu is dash (so this may complicate some of the features you are trying to
As for the script:
1. How are you guaranteeing that all 'sdir' found are directories?
# We will assume number 1 is true, ie all dirs at top level
2. , [0-9] and [[:digit:]] are all equivalent character lists
3. Parsing ls is generally a bad idea as pointed out here
4. Most probably reason for error is spacing in file names which the for loop will perform word splitting.
5. As per point 1, there is no guarantee you are processing files in the inner for loop.
6. Not sure why you are using process substitution (``) for the copy line when you are not returning the data to anything
7. Assuming you do have unusual characters in file and / or directory names then you should quote your variables being used in the copy
Just to make it clear, the named character class as enclosed by [::] is equal to a predefined set of characters. This is separate from the  character range expression. You generally use the first one inside the second one.
So [:digit:] is equal to 0-9, and [[:digit:]] is equal to [0-9].
By the way, the use of expr is generally unnecessary in most modern shells. Almost everything that it can do is now built-in in some form or other.
Here are a few ways to extract a string of digits using only shell built-ins (with a guess about your directory name format).
In fact, if there's only a single string of digits in the name, you could even use this:
They may take an extra line or two of code, but since everything is done internally, they should be more efficient than calling an external tool like expr.
thanks to all responders!
@David the H. Thank you; your explanations were very clear, and the links inserted very useful
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