#!/usr/bin/perl --
#
# Usage:
#    perl indentmk.pl < crud.mk > indented-crud.mk
#    perl indentmk.pl crud.mk crud.mk > indented-crud.mk
# 
# 
use strict;
use warnings;

Main( @ARGV );
exit( 0 );

sub Main {
    local *ARGV;
## uncomment to edit files and make backups instead of printing to STD
+OUT
#~     local $^I = ".orig";
    local @ARGV = @_;
    my $dent = 0;
    my $oldent = 0;
    my $space = "\t";
    LINE: while (defined($_ = <ARGV>)) {
        next if /^#/;
        
        my $w = /^\s*\.(\S+)/  ? $1 : '';
        if( $w ) {
            $oldent = $dent;
            if( $w =~ /^END/i ){
                $dent--;
                s/^/ $space x ( $dent )/e  ;
            } else {
                $dent++ if $w =~ /^IF/i;
                s/^/ $space x ( $dent - 1 )/e  ;
            }
        } else {
            s/^/ $space x ( $dent )/e;
        }
    }
    continue {
        die "-p destination: $!\n" unless print $_;
    }
}

__END__
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Example usage

$ perl indentmk.pl crud.mk > indented-crud.mk

$ cat crud.mk
CC                      *= gcc
CCTYPE          *= GCC
.IF "$(CCTYPE)" == "GCC"
GCC_MAJOR_VERSION *= 12
.IF  "$(GCC_MAJOR_VERSION)" == "4"
CFLAGS          += -static-libgcc
LIBC            += -static-libgcc
.ELSE
GCC_MAJOR_VERSION *= 42
.ENDIF
.ENDIF
.IF "$(CCTYPE)" == "GCC"
$(XCOPY) $(CCHOME)\bin\*dll ..\t\$(NULL)
.ENDIF


$ cat indented-crud.mk
CC                      *= gcc
CCTYPE          *= GCC
.IF "$(CCTYPE)" == "GCC"
        GCC_MAJOR_VERSION *= 12
        .IF  "$(GCC_MAJOR_VERSION)" == "4"
                CFLAGS          += -static-libgcc
                LIBC            += -static-libgcc
        .ELSE
                GCC_MAJOR_VERSION *= 42
        .ENDIF
.ENDIF
.IF "$(CCTYPE)" == "GCC"
        $(XCOPY) $(CCHOME)\bin\*dll ..\t\$(NULL)
.ENDIF
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