Removing occurences of #ifdef/#endif from a file with perl

Question

I have a code file that has some #ifdefs I would like removed in the header file after building a library. My first thought was to do this as a perl script that XCode can run. While I can certainly open the header file and read all content of it into a string in perl, I'm curious as to the best way to do the following

1. Find any occurrence of #ifdef EXAMPLE

2. Remove it and anything in between the following #endif

So the example is:

int i;
NSString *someString;
#ifdef EXAMPLE
NSString *exampleString;
#endif
bool done;

and the output would be:

int i;
NSString *someString;
bool done;

Options I'm considering:

• finding index of every #ifdef EXAMPLE and removing it via substring with the next found #endif
• Write a regex that can somehow remove these occurences.

Considering I haven't written Perl before (Objective-C is my primary language) I was curious if any XCode or Perl developers had any suggestions on what the best approach would be

Answer 1

I'm not sure why you want to strip out ifdefs, and you can probably use a C pre-processor to do this, but here's how you'd do it in Perl because it means I get to play with the flip-flop operator.

First thing is to craft a sufficient regex to match the ifdefs. IIRC they can be indented and there can be indentation between the # and the word.

#ifdef
#    ifdef
    #ifdef

Not sure if that last one is valid, but I'm going with it anyway.

my $ifdef_re = qr{^\s*#\s*ifdef\b};
my $endif_re = qr{^\s*#\s*endif\b};

If it was just removing text between #ifdef and #endif, Perl has the little used flip flop scalar .. operator.

#!/usr/bin/env perl

use strict;
use warnings;

my $ifdef_re = qr{^\s*#\s*ifdef\b};
my $endif_re = qr{^\s*#\s*endif\b};

while(<DATA>) {
    my $in_ifdef = /$ifdef_re/ .. /$endif_re/;

    print if !$in_ifdef;
}

__DATA__
int i;
NSString *someString;
#ifdef EXAMPLE
NSString *exampleString;
#endif
bool done;

But since we need to worry about nested ifdefs, its insufficient. A depth counter takes care of that.

#!/usr/bin/env perl

use strict;
use warnings;

my $ifdef_re = qr{^\s*#\s*ifdef\b};
my $endif_re = qr{^\s*#\s*endif\b};

my $ifdef_count = 0;
while(<DATA>) {
    $ifdef_count++ if /$ifdef_re/;

    print if $ifdef_count <= 0;

    $ifdef_count-- if /$endif_re/;
}

__DATA__
int i;
NSString *someString;
#ifdef EXAMPLE
NSString *exampleString;
#    ifdef FOO
this should not appear
#    endif
nor should this
#endif
bool done;