topic Re: Perl Regular Expression in SAS Programming

Perl Regular Expression

Rajaram — Wed, 16 Sep 2015 14:39:59 GMT

I am working on some RTF code generation. I am using following code that is working fine but i am not well in PRX functions.

Is there any way to simplyfy my code?

Code:

data _null_;
   length tmptxt $100.;
   tmptxt="a\b Refer $crossref(Table 1) and $italic.Section $crossref(3.1)$enditalic";
   tmptxt=prxchange('s/([\\{}])/\\$1/',-1,tmptxt);
   tmptxt= prxchange('s/([\$][a-zA-Z]+)([\(])/%$1$2/',-1,tmptxt);
   tmptxt=prxchange('s/%\$/%/',-1,tmptxt);
   tmptxt=prxchange('s/([\$][a-zA-Z]+)/&$1$2/',-1,tmptxt);
   tmptxt=prxchange('s/&\$/&/',-1,tmptxt);
   put tmptxt;
run;

Thanks in advance

Re: Perl Regular Expression

FriedEgg — Wed, 16 Sep 2015 16:47:10 GMT

You can reduce the number of PRXCHANGE functions by collapsing the two-step changes you are making for $->% and $->&


data _null_;
   length tmptxt $100.;
   tmptxt="a\b Refer $crossref(Table 1) and $italic.Section $crossref(3.1)$enditalic";
   tmptxt=prxchange('s/([\\{}])/\\$1/',-1,tmptxt);
   /*
      tmptxt=prxchange('s/([\$][a-zA-Z]+)([\(])/%$1$2/',-1,tmptxt);
      tmptxt=prxchange('s/%\$/%/',-1,tmptxt);
   */
   tmptxt=prxchange('s#[\$]([a-z]+)(?=\()#%$1#i',-1,tmptxt);
   /*
      tmptxt=prxchange('s/([\$][a-zA-Z]+)/&$1$2/',-1,tmptxt);
      tmptxt=prxchange('s/&\$/&/',-1,tmptxt);
   */
   tmptxt=prxchange('s#[\$]([a-z]+)#&$1#i',-1,tmptxt);
   put tmptxt;
run;

With comments removed:

data _null_;
   length tmptxt $100.;
   tmptxt="a\b Refer $crossref(Table 1) and $italic.Section $crossref(3.1)$enditalic";
   tmptxt=prxchange('s/([\\{}])/\\$1/',-1,tmptxt);
   tmptxt=prxchange('s#[\$]([a-z]+)(?=\()#%$1#i',-1,tmptxt);
   tmptxt=prxchange('s#[\$]([a-z]+)#&$1#i',-1,tmptxt);
   put tmptxt;
run;

Re: Perl Regular Expression

Jagadishkatam — Wed, 16 Sep 2015 17:33:56 GMT

I could help you to understand what the prxchange function is doing, as you are aware the prxchange function is used to replace the captured text and replace with another text or make it blank. Here are explanations of what the prxchange function is trying to do. prxchange is best for these kind of replacements.

prxchange('s/([\\{}])/\\$1/',-1,tmptxt); /* trying to locate any one of \\{} and replace with 
blank*/

prxchange('s/([\$][a-zA-Z]+)([\(])/%$1$2/',-1,tmptxt); /* Trying to locate to capture buffers
first capture for $ followed by any alphabet followed by + and second capture bufferfor \( 
and replace them with %*/

prxchange('s/%\$/%/',-1,tmptxt); /*

prxchange('s/%\$/%/',-1,tmptxt);/* trying to locate % followed by $ and when found this will be 
replaced with %*/

prxchange('s/([\$][a-zA-Z]+)/&$1$2/',-1,tmptxt); /* Trying to locate a text with $ followed by 
any small or capital letter alphabet followed by + , then this whole text is when identified 
will be replaced with &*/



prxchange('s/&\$/&/',-1,tmptxt); /* trying to locate the special character like & $ and 
replace with &*/

Thanks,

Jag

Re: Perl Regular Expression

Rajaram — Thu, 17 Sep 2015 09:24:41 GMT

Hi FriedEgg

Thanks a bunch.

I reduced my code

Could you explain two things

What is the role of ( )? becuase i misplaced in my code
I know ? is zero or one time. what is the meaning of ?=

Thanks in advance.

Rajaram

Re: Perl Regular Expression

FriedEgg — Thu, 17 Sep 2015 17:14:58 GMT

This is a non-capturing group that performs a positive look-ahead assertion.

[\$]([a-z]+)(?=\()

Options: case insensitive; ^ and $ match at line breaks

Match a $ character «[\$]»
Match the regular expression below and capture its match into backreference number 1 «([a-z]+)»
   Match a single character in the range between “a” and “z” «[a-z]+»
      Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
Assert that the regex below can be matched, starting at this position (positive lookahead) «(?=\()»
   Match the character “(” literally «\(»