Errata

my $regex = eval { qr/$pattern/ };
die "Check your pattern! $@" if $@;
while( <> ) {
if( m/$regex/ ) {
print "$_";
print "\t\t\$&: ",
substr( $_, $-[$i], $+[$i] - $-[$i] ), ## Error
"\n";
foreach my $i ( 1 .. $#- ) {
print "\t\t\$$i: ",
substr( $_, $-[$i], $+[$i] - $-[$i] ),
"\n";
}
}
}

## The first substr line is invalid. $i is not even initialized.

Note from the Author or Editor:
Change that line to

substr( $_, $-[0], $+[0] - $-[0] ),

m/[:alpha:]/ should be m/[[:alpha:]]/, and so on.
Otherwise, m/[:alpha:]/ matches a character from the class {:,a,l,p,h,a,:}.

Note from the Author or Editor:
Change as noted

Examples such as:

print "Didn't find spaces!\n" if $string =~ m/[:^space:]/;

don't do what the text suggests. Not finding spaces is not the same as finding non-spaces. There are four occurences of this (two with [:^, two with \P).

Note from the Author or Editor:
Those lines should read:


I negate those with a caret, C<^>, after the first colon:

print "Found non-alphabetics!\n" if $string =~ m/[[:^alpha:]]/;
print "Found non-spaces!\n" if $string =~ m/[[:^space:]]/;

I can say the same thing in another way by specifying a named property.
The C<\p{Name}> sequence (little p) includes the characters for the named
property, and the C<\P{Name}> sequence (big P} is its complement:

print "Found ASCII character!\n" if $string =~ m/\p{IsASCII}/;
print "Found control characters!\n" if $string =~ m/\p{IsCntrl}/;

print "Found non-punctuation characters!\n" if $string =~ m/\P{IsPunct}/;
print "Found non-uppercase characters!\n" if $string =~ m/\P{IsUpper}/;

$ perl tainted-args.pl
Argument [foo] is tainted

## Should be $ perl -T tainted-args.pl foo

Note from the Author or Editor:
Change as noted

The code line reads:

setuid( $<, $< )

but should be

setuid( $< );

Note from the Author or Editor:
Change as noted.