Perl regular expression to get number between PT and either M or H

[tarheel13]

Here is my desired output and sample data in datalines. Can someone help me with the Perl code to get the number that is between PT and M or PT and M? It's elapsed time since dose. I know there has to be a quicker way than using scan function. 

data times;
input pceltm $;
datalines;
PT30M
PT2H
PT4H
PT6H
;
run;

Thanks!

[Ksharp]

data times;
input pceltm $;
datalines;
PT30M
PT2H
PT4H
PT6H
PT6C
;
run;

data want;
 set times;
 pid=prxparse('/(?<=PT)\d+(?=M|H)/');
 call prxsubstr(pid,pceltm,p,l);
 if p then want=substr(pceltm,p,l);
 drop p l pid;
run;

[tarheel13]

It works but I only know prxmatch and prxchange. Can you explain what p and l do? I got that pid is the pattern id. 

[Ksharp]

p is position and l is length .
which could be used in SUBSTR() .

[PeterClemmensen · Accepted solution]

data times;
input pceltm $;
datalines;
PT30M
PT2H
PT4H
PT6H
;
run;

data want;
   retain r;
   if _N_ = 1 then r = prxparse('/PT(\d+)[HM]/');
   set times;
   if prxmatch(r, pceltm) then time = prxposn(r, 1, pceltm);
run;

[tarheel13]

Amazing! Thanks both!

[r_behata]

data times;
input pceltm $;
datalines;
PT30M
PT2H
PT4H
PT6H
;
run;


data want;
set times;
time=prxchange('s/(PT)(\d+)((M|H))/$2/',-1,pceltm);
run;