Errata

The paragraph with the mistake:
But if you (or a program) may be waiting impatiently for the output, you may wish to take that performance hit and flush the output buffer each time you print. See $! in the perlvar documentation for more information on controlling buffering in that case.

There is most likely a typo -- the $! is variable which contains recent errno value, while output autoflush control variable is a $|
Source: perldoc ( https://perldoc.perl.org/perlvar#$%7C and https://perldoc.perl.org/perlvar#$! )

Note from the Author or Editor:
Change as noted. The $! should be $|

Perl.org have upgraded to more secure connection.

Correct address:

https://learn.perl.org/

Note from the Author or Editor:
Update "http://learn.perl.org" to be "https://learn.perl.org", including the link

$rock_fh --> $rocks_fh

Note from the Author or Editor:
In the last line on the page, change $rock_fh to $rocks_fh

$rock_fh --> $rocks_fh

Note from the Author or Editor:
In the first line on the page, change $rock_fh to $rocks_fh

"Found a URL\n" --> "Found a .png\n"

Note from the Author or Editor:
In the second code block, change

if ( /\.png\z/ ) {
print "Found a URL\n";
}

to

if ( /\.png\z/ ) {
print "Found a PNG\n";
}

First comment should be "one or more digits" instead of "one or more digits before the decimal point"

Note from the Author or Editor:
In this example

/
[0-9]+ # one or more digits before the decimal point
[#] # literal pound sign
/x

Change as noted to

/
[0-9]+ # one or more digits
[#] # literal pound sign
/x

"the pattern /\.old$/" was not updated to corresponding "/\.old\z/" showed in the code example.

Note from the Author or Editor:
In the last paragraph, change:

So you use the pattern /\.old$/ to mean

to

So you use the pattern /\.old\z/ to mean

it could be better to add the comment "# or Ctrl-Z" for people who use Windows.

Note from the Author or Editor:
In the two code lines on that page that are:

print "Enter some lines, then press Ctrl-D:\n";

we can change that to

print "Enter some lines, then press Ctrl-D:\n"; # or Ctrl-Z on Windows

Perlbrew have upgraded to more secure connection.
Correct address: https://perlbrew.pl

Note from the Author or Editor:
Change URL to have https

= (binding operator) seems typo


Correct one:
=~ (binding operator)

Note from the Author or Editor:
Correct as noted.

Typo:
qw()()

Correct one:

qw()

Note from the Author or Editor:
In that index entry, there should be only one set of parentheses.