Perl: Append to file and get new line count - perl

Question

Quick question, and I'm sure it's something I'm doing completely wrong with variables, however, here is the issue.
Code first:
#!/usr/bin/perl
use strict;
use warnings;
my $File = "file.txt";
my $CurrentLinesCount = `wc -l < $File` or die "wc failed: $?";
chomp($CurrentLinesCount);
sub GetStatistics() {
if (-d $dir) {
print "Current Lines In File: $CurrentLinesCount\n";
}
else {
exit;
}
}
sub EditFile() {
my $editfile = $File;
my $text = "1234\n12345\n234324\n2342\n2343";
open(MYFILE,">>$editfile") || die("Cannot Open File");
print MYFILE "$text";
close(MYFILE);
sleep 5;
}
## MAIN
GetStatistics();
EditFile();
GetStatistics();
This is the output I get:
Current Lines In File: 258
Current Lines In File: 258
I verified that the file is being written and appended to. Can someone point me in the correct direction on how to have a variable set, updated, and then called again properly?

Answer 1

You call subs, not variables.
Try:
sub CurrentLinesCount {
my $CurrentLinesCount = `wc -l < $File` or die "wc failed: $?";
chomp($CurrentLinesCount);
return $CurrentLinesCount;
}
...
print "Current Lines In File: ", CurrentLinesCount(), "\n";

Answer 2

You're only doing the call to wc once. Thus you're setting the value of $CurrentLinesCount once, and you get the same number when you print it twice.
You'll have to redo the
$CurrentLinesCount = `wc -l < $File` or die "wc failed: $?";
line after you append to the file.
Edit: Or put that line in the GetStatistics function, which would probably be a better place for it.

Answer 3

I would probably move the code block
my $CurrentLinesCount = `wc -l < $File` or die "wc failed: $?";
chomp($CurrentLinesCount);
to the GetStatistics subroutine, so the variable is updated whenever you call your sub.

Answer 4

As an optimization, you can count how many lines you added rather than recounting the whole file (unless another process may also be writing to the file).
use strict;
use warnings;
use FileHandle;
use IPC::Open2;
our $CurrentLinesCount;
our $file = "file.txt";
sub CountLines {
my $File = shift;
my $CurrentLinesCount = `wc -l < $File` or die "wc failed: $?";
$CurrentLinesCount =~ s/\s+//g;
return $CurrentLinesCount;
}
sub ShowStatistics {
my $file = shift;
if (-f $file) {
print "Current Lines In File: $CurrentLinesCount\n";
} else {
exit;
}
}
sub EditFile {
my $editfile = shift;
my $sleeptime = shift || 5;
my $text = "1234\n12345\n234324\n2342\n2343";
open(MYFILE,">>$editfile") || die("Cannot Open File");
print MYFILE "$text";
close(MYFILE);
# Look here:
my $pid = open2(*Reader, *Writer, "wc -l" );
print Writer $text;
close Writer;
$CurrentLinesCount += <Reader>;
sleep $sleeptime;
}
$CurrentLinesCount = CountLines($file);
ShowStatistics($file);
# EditFile updates $CurrentLinesCount
EditFile($file, 2);
ShowStatistics($file);
Still one too many globals for my taste, but I suppose this isn't a program of consequence. On the other hand, globals can be habit forming.
Note that wc doesn't count anything after the final "\n" when counting lines (it views "\n" as a line terminator). If you want to view "\n" as a line separator and count those trailing characters as a line, you'll need an alternate method of counting lines.