Re: [PLUG] bash script help needed (take 2)

[Art Alexion <art.alexion@verizon.net>]

bergman@merctech.com wrote:

>Ooops...I sent the wrong version of my reply...see below for the full info...
>  
>
Yeah.  This is more like what is happening.

>In the message dated: Wed, 22 Feb 2006 09:39:56 EST,
>The pithy ruminations from Art Alexion on 
><[PLUG] bash script help needed> were:
>
>=> 
>=> I am trying to iron out a script that renames all files in a current
>=> directory to replace embedded spaces with underscores, and makes
>=> everything lower case.
>
>A common need...and a fun "quiz" type interview question.
>
>=> 
>=> The suggestion that I was given was (in pertinent part):
>=> 
>=> for OLD in *
>=>   do
>=>     NEW=`echo $OLD|sed s/\ /\_/g | tr [:upper:] [:lower:]`
>=>     echo "OLD=\"$OLD\""
>=>     echo "NEW=\"$NEW\""
>=>     echo -e "mv \"$OLD\" \"$NEW\"\n"
>=>   done
>=> 
>=> But while the messages sent to the console indicated what I wanted to do
>=> was happening, and there were no errors reported, no changes were
>=> actually being made to the filenames.
>=> 
>=> I read the echo man page and it seemed that the line
>=> 
>=> echo -e "mv \"$OLD\" \"$NEW\"\n"
>=> 
>=> didn't actually execute the mv command, so I added the line
>=> 
>=> mv $OLD $NEW
>
>OK.
>
>
>=> 
>=> after it, so it now reads
>=> 
>=> for OLD in *
>=>   do
>=>     NEW=`echo $OLD|sed s/\ /\_/g | tr [:upper:] [:lower:]`
>=>     echo "OLD=\"$OLD\""
>=>     echo "NEW=\"$NEW\""
>=>     echo -e "mv \"$OLD\" \"$NEW\"\n"
>=>     mv $OLD $NEW
>=>   done
>=> 
>=> But this results in the error
>=> 
>=> mv: when moving multiple files, last argument must be a directory
>
>Good. You're actually lucky to get this message. I've seen instances where this 
>kind of simple programming error has destroyed a production e-commerce database 
>server...
>
>What doe the echo statements display before the error message? Are they:
>
>	OLD="*"
>	NEW="*"
>	mv "*" "*"
>
>That's what I'd expect if there are no files or directories in the current directory.
>
>If there are files in the current directory with spaces in their names, then
>you'd see something like:
>	OLD="file name with spaces"
>	NEW="file_name_with_spaces"
>	mv "file name with spaces" "file_name_with_spaces"
>However, the mv command actually gets called as:
>
>	mv  file name with spaces  file_name_with_spaces
>
>(note the lack of quotes). Thus, mv receives the following arguments:
>
>	file
>	name
>	with
>	spaces
>	file_name_with_spaces
>
>and promptly checks if "file_name_with_spaces" is a directory. If not, you get
>an error message.
>
>Try changing the mv command to:
>	mv "$OLD" "$NEW"
>
>=> 
>=> even though $NEW does not yet exist, so I am not really moving multiple
>=> files.
>
>The issue isn't that $NEW doesn't exist, but either that the initial
>expansion of the "*" wildcard failed to produce a list of files to be
>renamed, thus the literal character "*" is passed to the mv command,
>or that the expansion succeeded, and spaces are being passed to the
>mv command.
>
>=> 
>=> What am I doing wrong?
>
>Well, what you're "doing wrong" is not checking or escaping whitespace
>in the results of the metacharacter expansion before calling mv(1). The
>action of mv will vary, depending on what files and directories are in
>the directory where the script is executing.
>
>
>I'd suggest that you go back and take another look at the thread "Interactive 
>rm" from a couple of weeks ago. That thread deals with this very issue--how the 
>shell handles wildcard expansion.
>
>You may also want to look at:
>
>	http://www.oreilly.com/catalog/bash3/
>	http://www.oreilly.com/catalog/shellsrptg/
>  
>


-- 

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Art Alexion
Arthur S. Alexion LLC

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