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I'm using the following script which takes the data from a html form and stores in a Postgres DB. There is this pg_escape_string function which stores the value from the form to the php variable. Searching the web throughout, I found that pg_escape_string escapes a string for insertion into the database. I'm not much clear on this. What does it actually escaping? What actually happens when its said that a string is escaped?
<html>
<head></head>
<body>
<?php
if ($_POST['submit']) {
// attempt a connection
$dbh = pg_connect("host=localhost dbname=test user=postgres");
if (!$dbh) {
die("Error in connection: " . pg_last_error());
}
// escape strings in input data
$code = pg_escape_string($_POST['ccode']);
$name = pg_escape_string($_POST['cname']);
// execute query
$sql = "INSERT INTO Countries (CountryID, CountryName) VALUES('$code', '$name')";
$result = pg_query($dbh, $sql);
if (!$result) {
die("Error in SQL query: " . pg_last_error());
}
echo "Data successfully inserted!";
// free memory
pg_free_result($result);
// close connection
pg_close($dbh);
}
?>
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
Country code: <br> <input type="text" name="ccode" size="2">
<p>
Country name: <br> <input type="text" name="cname">
<p>
<input type="submit" name="submit">
</form>
</body>
</html>
426
Consider the following code:
$sql = "INSERT INTO airports (name) VALUES ('$name')";
Now suppose that $name is "Chicago O'Hare". When you do the string interpolation, you get this SQL code:
INSERT INTO airports (name) VALUES ('Chicago O'Hare')
which is ill-formed, because the apostrophe is interpreted as a SQL quote mark, and your query will error.
Worse things can happen, too. In fact, SQL injection was ranked #1 Most Dangerous Software Error of 2011 by MITRE.
But you should never be creating SQL queries using string interpolation anyway. Use queries with parameters instead.
$sql = 'INSERT INTO airports (name) VALUES ($1)';
$result = pg_query_params($db, $sql, array("Chicago O'Hare"));
pg_escape_string() prevent sql injection in your code
28
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