perl : String extraction based on pattern match [closed] - string

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Closed 10 years ago.
A file FILE1 has several thousands of lines with a terminating pattern _Pattern1.
A second file too has several thousands of lines with the same terminating pattern _Pattern1.
I must now:
Read FILE1 line by line
Find out if the line has any string terminating with _Pattern1
Extract the string and store it into a variable
Open FILE2 and read it line by line
Find out if the line just read from FILE2 contains the string stored in the variable above
How is this to be done in perl?
EDIT2:
Allright, with a bit of googling and referring to the links enlisted below, I solved my problem.
Here is the code snippet.
#!/usr/bin/perl
use strict;
use warnings;
my $OriginalHeader=$ARGV[0]; ## Source file
my $GeneratedHeader=$ARGV[1];## File to compare against
my $DeltaHeader=$ARGV[2]; ## File to store misses
my $MatchingPattern="_Pos";
my $FoundPattern;
open FILE1, $OriginalHeader or die $!;
open FILE2, $GeneratedHeader or die $!;
open (FILE3, ">$DeltaHeader") or die $!;
my $lineFromOriginalHeader;
my $lineFromGeneratedHeader;
my $TotalMacrosExamined = 0;
my $TotalMacrosMissed = 0;
while($lineFromOriginalHeader=<FILE1>)
{
if($lineFromOriginalHeader =~ /$MatchingPattern/)
{
my $index = index($lineFromOriginalHeader,$MatchingPattern);
my $BackIndex = $index;
my $BackIndexStart = $index;
$BackIndex = $BackIndex - 1;
## Use this while loop to extract the substring.
while (1)
{
my $ExtractedChar = substr($lineFromOriginalHeader,$BackIndex,1);
if ($ExtractedChar =~ / /)
{
$FoundPattern = substr($lineFromOriginalHeader,$BackIndex + 1,$BackIndexStart + 3 -
$BackIndex);
print "Identified $FoundPattern \n";
$TotalMacrosExamined = $TotalMacrosExamined + 1;
##Skip the next line
$lineFromOriginalHeader = <FILE1>;
last;
}
else
{
$BackIndex = $BackIndex - 1;
}
} ##while(1)
## We now look for $FoundPattern in FILE2
while ($lineFromGeneratedHeader = <FILE2>)
{
if (index($lineFromGeneratedHeader,$FoundPattern)!= -1)
{
##Pattern found. Reset file pointer and break out of while loop
seek FILE2,0,0;
last;
}
else
{
if (eof(FILE2) == 1)
{
print FILE3 "Generated header misses $FoundPattern\n";
$TotalMacrosMissed = $TotalMacrosMissed + 1;
seek FILE2,0,0;
last;
}
}
} ##while(1)
}
else
{
##NOP
}
} ##while (linefromoriginalheader)
close FILE1;
close FILE2;
close FILE3;
print "Total number of bitfields examined = $TotalMacrosExamined\n";
print "Number of macros obsolete = $TotalMacrosMissed\n";

Answer 1

Just a first cut at making your code more Perly. Actually plenty more could be done, including $some_var is usually used vs $SomeVar in Perl, but I didn't get that far.
#!/usr/bin/perl
use strict;
use warnings;
my ($OriginalHeader, $GeneratedHeader, $DeltaHeader) = #ARGV;
my $MatchingPattern=qr/(\S*_Pos)/; # all non-whitespace terminated by _Pos
open my $file1, '<', $OriginalHeader or die $!;
open my $file2, '<', $GeneratedHeader or die $!;
open my $file3, '>', $DeltaHeader or die $!;
my $TotalMacrosExamined = 0;
my $TotalMacrosMissed = 0;
while(my $lineFromOriginalHeader=<$file1>) {
next unless $lineFromOriginalHeader =~ $MatchingPattern;
my $FoundPattern = $1; # matched string
print "Identified $FoundPattern \n";
$TotalMacrosExamined++;
##Skip the next line
<$file1>;
## We now look for $FoundPattern in FILE2
my $match_found = 0;
while (my $lineFromGeneratedHeader = <$file2>) {
if (index($lineFromGeneratedHeader,$FoundPattern)!= -1) {
##Pattern found. Close the file and break out of while loop
$match_found++;
last;
}
}
unless ($match_found) {
print $file3 "Generated header misses $FoundPattern\n";
$TotalMacrosMissed++;
}
seek $file2,0,0;
}
print "Total number of bitfields examined = $TotalMacrosExamined\n";
print "Number of macros obsolete = $TotalMacrosMissed\n";

Answer 2

Having programmed in C all my life, I googled usage of the perl constructs below and wrote a C like program. This works flawlessly for me. :-)
Edit : This is to clarify why I must skip a line in the algo below. The pattern which is retrieved and later searched for in the second file occurs on two consecutive lines. It therefore suffices that its first occurence is reliably detected. Also a nitpick, It is always guaranteed that the substring containing the pattern is always the second substring on the line.
e.g #define Something_Pos (Some Value)
#!/usr/bin/perl
use strict;
use warnings;
my $OriginalHeader=$ARGV[0];
my $GeneratedHeader=$ARGV[1];
my $DeltaHeader=$ARGV[2];
my $MatchingPattern="_Pos";
my $FoundPattern;
open FILE1, $OriginalHeader or die $!;
open FILE2, $GeneratedHeader or die $!;
open (FILE3, ">$DeltaHeader") or die $!;
my $lineFromOriginalHeader;
my $lineFromGeneratedHeader;
my $TotalMacrosExamined = 0;
my $TotalMacrosMissed = 0;
while($lineFromOriginalHeader=<FILE1>)
{
if($lineFromOriginalHeader =~ /$MatchingPattern/)
{
my $index = index($lineFromOriginalHeader,$MatchingPattern);
my $BackIndex = $index;
my $BackIndexStart = $index;
$BackIndex = $BackIndex - 1;
## Use this while loop to extract the substring.
while (1)
{
my $ExtractedChar = substr($lineFromOriginalHeader,$BackIndex,1);
if ($ExtractedChar =~ / /)
{
$FoundPattern = substr($lineFromOriginalHeader,$BackIndex + 1,$BackIndexStart + 3 -
$BackIndex);
print "Identified $FoundPattern \n";
$TotalMacrosExamined = $TotalMacrosExamined + 1;
##Skip the next line
$lineFromOriginalHeader = <FILE1>;
last;
}
else
{
$BackIndex = $BackIndex - 1;
}
} ##while(1)
## We now look for $FoundPattern in FILE2
while ($lineFromGeneratedHeader = <FILE2>)
{
##print "Read the following line from FILE2: $lineFromGeneratedHeader\n";
if (index($lineFromGeneratedHeader,$FoundPattern)!= -1)
{
##Pattern found. Close the file and break out of while loop
seek FILE2,0,0;
last;
}
else
{
if (eof(FILE2) == 1)
{
print FILE3 "Generated header misses $FoundPattern\n";
$TotalMacrosMissed = $TotalMacrosMissed + 1;
seek FILE2,0,0;
last;
}
}
} ##while(1)
}
else
{
}
} ##while (linefromoriginalheader)
close FILE1;
close FILE2;
close FILE3;
print "Total number of bitfields examined = $TotalMacrosExamined\n";
print "Number of macros obsolete = $TotalMacrosMissed\n";