The example you linked to deals with files with fixed-length records - i.e. generally binary files. As you're talking about "line by line", I assume you're talking about a text-based file - e.g. plain text, HTML, CSV, etc.
# Set the character which will be used to indicate the end of a line.
# This defaults to the system's end of line character, but it doesn't
# hurt to set it explicitly, just in case some other part of your code
# has altered it from the default.
local $/ = "\n";
# Open the file for read access:
open my $filehandle, '<', 'myfile.txt';
my $line_number = 0;
# Loop through each line:
while (defined($line = <$filehandle>))
{
# The text of the line, including the linebreak
# is now in the variable $line.
# Keep track of line numbers
$line_number++;
# Strip the linebreak character at the end.
chomp $line;
# Do something with the line.
do_something($line);
# Perhaps bail out of the loop
if ($line =~ m/^ERROR/)
{
warn "Error on line $line_number - skipping rest of file";
last;
}
}
But we can make the above more concise, because Perl usefully defines a variable called $_ which is used as a default variable in many cases; and a variable called $. which keeps track of the current line number.
# Set the character which will be used to indicate the end of a line.
local $/ = "\n";
# Open the file for read access:
open my $filehandle, '<', 'myfile.txt';
# Loop through each line:
while (<$filehandle>)
{
# The text of the line, including the linebreak
# is now in the variable $_.
# Strip the linebreak character at the end.
chomp;
# Do something with the line.
do_something($_);
# Perhaps bail out of the loop
if (m/^ERROR/)
{
warn "Error on line $. - skipping rest of file";
last;
}
}
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