Re: Multiple files

[Simon Law <sfllaw@engmail.uwaterloo.ca>]

On 31 May 2002, Daniel D Jones wrote:

> How does one handle multiple files via most command line utilities?  For
> example, suppose you have a handful of perl scripts (*.pl) and you want
> to save them in the same directory with a different extension.  The
> command
> 
> cp *.pl *.bak
> 
> complains that you're copying multiple files but the last command isn't
> a directory.

	That's right.  Say you have a directory that looks like this:

$ ls
bar.pl  baz.pl  foo.pl

	Then, by shell globbing, `cp *.pl *.bak` expands to: 
`cp bar.pl baz.pl foo.pl` which would be copying two files into one
non-directory.  Obviously, incorrect.

> Or suppose you have a series of perl scripts which are saved in DOS
> line-end format.  The extra ^M on the bang line causes bash not to
> recognize the path to perl, and the script to fail.  Sounds like a job
> for sed.
> 
> sed s/^M// *.pl > *.unix

	sed doesn't QUITE work that way.  And you have that same problem
with globbing.

> Again, the file naming criteria doesn't work.  I could write a script
> which essentially generates a new command for each file fitting the
> naming pattern, or perhaps use find -exec but there's got to be a
> straightforward way to do this on the command line.  Doesn't there?

	The most straight-forward and portable Bourne way of doing this
is with a loop:

$ for i in *.pl; do cp $i `echo $i | sed -e 's/\.pl$/\.bak/'`; done

	So let's dissect this:

for i in *.pl; do ...; done
	Iterate over all the *.pl files in the directory, and use $i
	as the counter variable.

cp $i `...`
	Copy the file in counter $i to the name returned by the
	commands executed in `...` on stdout.

echo $i | sed -e 's/\.pl$/\.bak/'
	Replace the .pl extension at the end of $i with .bak

	Now, if you use GNU bash as your shell, you can simplify the
command by avoiding sed, and using the built-in pattern matching:

$ for i in *.pl; do cp $i ${i%.pl}.bak; done

Simon


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