I'm a newbie to SQL. When I tried to run a CGI with this:

my $sth = $dbh->prepare(<<SQL) or die $dbh->errstr;
select count(*) from userlist
where colemail = \'$FORM{'email'}\';
SQL

$sth->execute;
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I get a 500 error.

Drop the semicolon. A lot of SQL engines trip over them.

Taint error. Why aren't you using placeholders? Even if this could work for well-behaved user data entries, it can still easily fail for others. Using a placeholder would prevent that.

And if you've connected to the database with the raiseError attribute set to true, there's no need for the or die... part.

my $sth = $dbh->prepare(<<SQL);
select count(*) from userlist
where colemail = ?
SQL

$sth->execute($FORM{email});
[download]