Moving files

[pll at lanminds.com]

In a message dated: Mon, 06 Jan 2003 11:32:55 EST
Michael O'Donnell said:

>>        perl -e 'opendir DIR,".";@f = grep { ! /^\./ && -f $_ } readdir(DIR);
>\
>>          map {($n = $_)=~ s/\s+/_/g; rename ($_, $n) } @f;'
>
>On a more serious note, I (for one) would be grateful for
>a blow-by-blow analysis of what you've done, since I'm in
>trying to learn how to look at Perl code without my eyes
>automatically crossing...

Keep in mind that perl one liners are not necessarilly the easiest 
thing to learn from, however, this is pretty straighforward.  
References are in ()s:

	perl -e	                 # execute the following snipped of code (perlrun)

	opendir DIR,"."          # open the directory "." and assign 
                                 # file handle DIR, same as open() for a file
                                 # (perlfunc)

	@f =                     # assign the following to an array named 'f'
                                 # (perlsyn)

        grep {                   # user perl's grep function to match 
                                 # what comes next in the {} against the list
                                 # of things at the end (perlfunc)

	! /^\./                  # anything not beginning with a '.' (perlre)

	&&                       # and operator (perlop)

	-f                       # file test operator (perlop)

        $_                       # magic var, default "thing" being 
                                 # operated on in a loop context usually (perlvar)

	}                        # end grep block

        readdir (DIR)            # reads from the file handle DIR (perlfunc)

        map {                    # basically creates a 'for' loop 
                                 # around the block contained in {} and
                                 # operates on the list at the end (perlfunc)

       ($n = $_)=~ s/\s+/_/g;    # Assing val of $_ to $n *after* s/\s+/_/g
                                 # (perlre, perlop for =~)

       rename ($_, $n)           # use rename to 'mv' the file from 
                                 # the old to the new name (perlfunc)

       }                         # end map block

       @f                        # the list previously created with the grep call 
			

The one liner might make more sense if formatted more like a real 
program:

    perl -e '\
             opendir DIR,".";\
             @f = grep { ! /^\./ && -f $_ } readdir(DIR);\
             map {($n = $_)=~ s/\s+/_/g;\
             rename ($_, $n) } @f;\
            '

This way it's pretty obvious what the individual steps are:

    perl -e '\                                         # exec a code snippet
         opendir DIR,".";\                             # open the cwd
         @f = grep { ! /^\./ && -f $_ } readdir(DIR);\ # find files that ! ^\.
         map {($n = $_)=~ s/\s+/_/g;\                  # replace ' ' w/ '_'
         rename ($_, $n) } @f;\                        # rename the file
         '
HTH,
-- 

Seeya,
Paul
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