regular expression url rewrite based on folder

Question

I need to be able to take /calendar/MyCalendar.ics where MyCalendar.ics coudl be about anything with an ICS extention and rewrite it to /feeds/ics/ics_classic.asp?MyCalendar.ics

Thanks

Answer 1

C:\x>perl foo.pl
Before: a=/calendar/MyCalendar.ics
After: a=/feeds/ics/ics_classic.asp?MyCalendar.ics

...or how about this way?
(regex kind of seems like overkill for this problem)
b=/calendar/MyCalendar.ics
index=9
c=MyCalendar.ics (might want to add check for ending with '.ics')
d=/feeds/ics/ics_classic.asp?MyCalendar.ics

Here's the code:

C:\x>type foo.pl
my $a = "/calendar/MyCalendar.ics";
print "Before: a=$a\n";
my $match = (
   $a =~ s|^.*/([^/]+)\.ics$|/feeds/ics/ics_classic.asp?$1.ics|i
);
if( ! $match ) {
   die "Expected path/filename.ics instead of \"$a\"";
}
print "After: a=$a\n";
print "\n";
print "...or how about this way?\n";
print "(regex kind of seems like overkill for this problem)\n";
my $b = "/calendar/MyCalendar.ics";
my $index = rindex( $b, "/" ); #find last path delim.
my $c = substr( $b, $index+1 );
print "b=$b\n";
print "index=$index\n";
print "c=$c (might want to add check for ending with '.ics')\n";
my $d = "/feeds/ics/ics_classic.asp?" . $c;
print "d=$d\n";
C:\x>

General thoughts:

If you do solve this with a regex, a semi-tricky bit is making sure your capture group (the parens) exclude the path separator. Some things to consider:

Are your paths separators always forward-slashes?

Regex seems like overkill for this; the simplest thing I can think of of to get the index of your last path separator and do simple string manipulation (2nd part of sample program).

Libraries often have routines for parsing paths. In Java I'd look at the java.io.File object, for example, specifically getName() Returns the name of the file or directory denoted by this abstract pathname. This is just the last name in the pathname's name sequence

Answer 2

Regular expressions are meant for searching/matching text. Usually you will use regex to define what you search for some text manipulation tool, and then use a tool specific way to tell the tool with what to replace the text.

Regex syntax use round brackets to define capture groups inside the whole search pattern. Many search and replace tools use capture groups to define which part of the match to replace.
We can take the Java Pattern and Matcher classes as example. To complete your task with the Java Matcher you can use the following code:

Pattern p = Pattern.compile("/calendar/(.*\.(?i)ics)");

Matcher m = p.matcher(url);

String rewritenUrl = "";
if(m.matches()){
    rewritenUrl = "/feeds/ics/ics_classic.asp?" + url.substring( m.start(1), m.end(1)); 
}

This will find the requested pattern but will only take the first regex group for creating the new string.

Here is a link to regex replacement information in (imho) a very good regex information site: http://www.regular-expressions.info/refreplace.html