unless ( open( FILE, "name_of_file" ) ) {
    die "Could not open file for reading\n";
}

##</code><code>##

while (<FILE>) {
    if ($_ =~ /^(maintenance_mode)\s([\w,=]*)$/) {

##</code><code>##

$var =~ /whatever/;

##</code><code>##

$_ =~ /whatever/;

##</code><code>##

/whatever/;

##</code><code>##

for ($foo) {
    s/^"//;
    s/"$//;
    s/\W+/-/;
}
# or also:
# s/^"//, s/"$//, s/\W+/-/ for $foo;

##</code><code>##

    $hash{$1} = $2;

    }
}