如何在同一Perl脚本中读取整个文件和逐行文件

Question

Whenever I want Perl to read the whole file I put undef $/ before reading the file. I tried to find more information about the variable $/ but without success.

What I need to do is to write a script in Perl that first reads the whole file to a variable and then read another file line by line. How could this be done?

Answer 1

You can try opening and reading the first file in a local scope, and then limit the setting of $/ to that scope.

my $firstfile;
{
    open my $fh, '<', $file or die;
    local $/ = undef;
    $firstfile = <$fh>;
    close $fh;
}

# continue with $/ still set

Link:

http://perlmaven.com/slurp (section: localize the change)

Either that, or save the value of $/ to another variable before setting it to undef , and then reset it after reading the first file.

If you don't want to use $/ , look into File::Slurp . There is a section on using it in the link I provided.

Answer 2

Here's another way to do it without directly using $/.

You can use File::Slurp's read_file to read the first file and store its data in memory.

my $text = read_file('filename');
my $bin = read_file('filename' { binmode => ':raw' });
my @lines = read_file('filename');
my $lines = read_file('filename', array_ref => 1);

And, the simplest reading method to read the second file line by line.

open(my $fh, '<', 'input.txt');
while (my $line = <$fh>) {
    ...
}
close $fh;