[Gprename-users] Perl backreferences in GPRename in Replace/Remove

[Zurd <zu...@ya...>]

> Ooups ... your reply as been "junked" by my mail client
> I was thinking that my question was so stupid that it didn't worth 
> answering ;-)

Not at all, your question is actually one of the most "head scratching" I've
got since I first started coding GPRename !

Thanks for the clarification and the examples, I've searched a lot the internet
for information on this and I've learned what is "backreferences" in Perl
Regular Expression.

Now, here's a little perl script that I've made, if you copy that in a text file
and call it by "perl file" it will produce the result "x = 7"
It's really quite simple, if it match a digit, here the number 7, then print this
number, and it do.  Backreference works perfectly well here.
$x = "7";
$x =~ s/([0-9])/$1/g;
print "x = $x\n";

Now another example, the same thing, but this one's not working.  It will print
"a =", not printing the number 7 :
$a = "7";
$b = "$1";
$a =~ s/([0-9])/$b/g;
print "a = $a\n";

After much research, it looks like that $1 from $b is treated as an empty
variable, so it doesn't print anything.  But if you call $b = '$1'; 
(single quote instead of double quotes), it's going to treat $1 completely 
as a string and print the string '$1', not a backreference, which is what
GPRename is doing, unfortunately.

Here's the GPRename code doing this :
$new_name =~ s/$replace_this/$replace_with/g;
It's a simple Perl Regular Expression using Substitution, which is exactly
the same as the first example, which shoud work the way we want it to, 
not much I can change here.

Someone on #perl on IRC gave me this trick which works :
$g = "7";
$h = "1";
$g =~ s/([0-9])/$$h/g;
print "g = $g\n";
It sure looks strange and is not a standard, but in a shell script, it works!
In GPRename, it doesn't work, it says :
Can't use string ("1") as a SCALAR ref while "strict refs"
Whatever, that way is not clean and useful, so let's not bother with this.

And now I'm almost out of idea on what to do.  I've searched the web a lot and
I didn't found anything useful.  The last thing I tought, was to install KRename 
and see if it works in their software, if it does, then I'll have a look at 
their code and see if I can implement the same thing in GPRename.

Else I will post a note in Help/Tips that backreferences in Replace/Remove
cannot be use.

As for your files, since you said there's another way to rename them, well go
ahead, for now it's the best way to deal with them :-)

And actually, I'd say there's always another way to rename files without
backreferences, so it's not a big loss if I can't implement it ;-)




> > --- Hippo31 <hi...@fr...> a écrit :
> Actually i want to modify filenames by reusing some part of the original 
> one, example:
> DBZ - 277 Prochaine victime la Terre HQ-FR-Jaxx21.avi
> replace with
> DBZ 277 - Prochaine victime la Terre HQ-FR-Jaxx21.avi
> 
> Backreferences are extremely useful in this case (even if this is not 
> the only way to do it).
> With sed it could be made like this:
> echo "DBZ - 277 Prochaine victime la Terre HQ-FR-Jaxx21.avi" | sed 's/- 
> \([0-9][0-9][0-9]\)/\1 -/'
> As you can see i have put the group of tree digits in the search pattern 
> between (necessary escaped) brackets which places it in the first 
> "pattern space". I call it back in the replace pattern using the \1 
> special key
> Of course perl allows this kind of substitute constructions and even 
> simpler !
> filename = s/- (\d+)/$1 -/;
> Which could be translated in full word in: "REPLACE a minus followed by 
> a space followed by (being of the pattern space) one digit (\d) or more 
> (+) (end of the pattern space) BY 1st pattern space followed by a space 
> followed a minus"
> 
> To come back with gprename when i try this kind of substitution i get
> DBZ $1 - Prochaine victime la Terre HQ-FR-Jaxx21.avi
> so ... no call back of the pattern space.



> Zurd a écrit :
> > Well, I'm not an expert on perl regular expression and your command almost
> > looks cryptic to me ;-)
> >
> > As I understand, you want to switch the "- " to the end of the filename?
> >
> > If you could provide me with a few filenames examples I'll be able to better grasp
> > what you're trying to achieve.
> >
> > What I'm sure of though, is that if you use the Perl Regular Expression checkbox,
> > the replace/with becomes a normal substitute regular expression like
> > sed 's/replace_this_field/with_this_field/g'


> > --- Hippo31 <hi...@fr...> a écrit :
> >   
> >> Hello,
> >> I recently discorered this nice tool and feel it quite useful, but i 
> >> would like to make a replacement like this "s!- (\d+)!\1 -!"
> >> Through gprename i have tried
> >> Replace "- (\d+)" with "\1 -"
> >> and also
> >> Replace "- (\d+)" with "$1 -"
> >>
> >> but the displayed result doesn't look like what i was expected
> >>
> >> Isn't there possible to use the backreferences in the target space ?
> >>
> >> Hippo31

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