preg_replace() pattern "/ /" delimiter will not work with $_POST variable.

[sabinmash]

preg_replace() asks that "Delimiter must not be alphanumeric or backslash" in the pattern.  So I changed

 

$new_text = preg_replace($_POST['withthis'] ,$_POST['withthis'],$_POST['text']);

to this

$replacethis = $_POST['replacethis'];
$new_text = preg_replace("/$replacethis/",$_POST['withthis'],$_POST['text']);

It works fine, but out of curiosity, is there any way to have the POST variable as a parameter directly, and why does it not work? 

 

Just to try it, I attempted: "/$_POST['withthis']/"  and $_POST["/'withthis'/"] and both do not work.  str_replace is a better option I think, but I am just trying to get a better understanding of this delimiter rule.  Thanks for your time!

[scootstah]

Sure, if the $_POST variable contains the delimiters.

$_POST['pattern'] = '/hello/';

$foo = 'hello world';

$foo = preg_replace($_POST['pattern'], '', $foo);

echo $foo;

 

Outputs " world".

[xyph]

You'd have to escape any existing delimiters within the expression.

 

For example '~delim~iter~' is bad. '~delim\~iter~' is good.

 

You'd have to use str_replace to replace every instance of '~' with '\~' before you used it in the preg_* functions.

 

~ can be any valid delimiter.

[scootstah]

You'd have to escape any existing delimiters within the expression.

 

For example '~delim~iter~' is bad. '~delim\~iter~' is good.

 

You'd have to use str_replace to replace every instance of '~' with '\~' before you used it in the preg_* functions.

 

~ can be any valid delimiter.

 

True, but then again if the pattern already had escaped delimiters then you'd totally botch it up.

 

For example if the pattern was "~a string with \~ in it~" then it would end up "~a string with \\~ in it~".

 

So you'd need regex to validate your regex. o.O

[Psycho]

I think part of his question is also why he couldn't use the POST value directly inside the parens with the forwardslashes such as

"/$_POST['withthis']/"

 

As I am sure you know, you can use variables directly inside a double quoted string. But, when you have an array value with quotes around the key, PHP gets confused. The simple solution is to enclose the variables inside curly braces. I try to do this for ALL my variables within double quoted strings out of habit so I don't have to worry about the scenarios where they would fail.

 

This should work for you.

$new_text = preg_replace("/{$_POST['replacethis']}/" ,$_POST['withthis'],$_POST['text']);

[scootstah]

The simple solution is to enclose the variables inside curly braces. I try to do this for ALL my variables within double quoted strings out of habit so I don't have to worry about the scenarios where they would fail.

 

I find that syntax ugly, so I always concatenate.

 

Actually, I find double quotes to be ugly in general so I avoid them like the plague unless I need to use special characters (like \n).

[Psycho]

I find that syntax ugly, so I always concatenate.

 

Actually, I find double quotes to be ugly in general so I avoid them like the plague unless I need to use special characters (like \n).

 

Well, I find breaking in and out of quotes to concatenate things ugly. So, there. Thankfully, PHP supports both ways of working with strings/variables, your way and the right way 

 

Plus, I find it hilarious when I see people do this (note the end of the string) which I see all the time.

$query = 'SELECT * FROM table_name WHERE field_id = ' . $fieldID . '';

 

But, to each his own.

 

EDIT: I suppose that breaking out of quotes to concatenate a variable would make sense if you cannot easily differentiate your variables inside the strings. But, that is an editor dependent issue. The editor I use makes it easy for me to 'see' the variables in the quoted strings. Something to think about if your editor does not do that for you.

[scootstah]

Thankfully, PHP supports both ways of working with strings/variables, your way and the right way 

 

Pssshhh.

 

Plus, I find it hilarious when I see people do this (note the end of the string) which I see all the time.

$query = 'SELECT * FROM table_name WHERE field_id = ' . $fieldID . '';

 

I do use double quotes for queries like that, but I still concatenate it. So it would look like this:

$query = "SELECT * FROM table_name WHERE field_id = '" . $fieldID . "'";

 

Meh. I usually use a database wrapper so I hardly ever write a query like that anyway.

[xyph]

Why wouldn't you just use

 

SELECT `whatever` FROM `table` WHERE `column` = "value"

 

I'm not sure about mysql_real_escape_string(), but I know for sure mysqli->escape_string() escapes doulbe quotes as well.

 

From what I understand, MySQL treats single and double quotes the same.

[scootstah]

We're talking about storing the query in a variable.

[xyph]

$query = 'SELECT `whatever` FROM `table` WHERE `column` = "' . $value . '"';

 

I understand that. I was referring to why you'd use double quotes around a MySQL query string. Why wouldn't you continue to use single quotes, and instead double-quote strings within the query.

[Psycho]

I think you both missed what I was talking about. I see a lot of people that continually enter/exit the quoted string to concatenate variables where the string they are wanting to create needs to end with a variable. But, I routinely see them concatenating a null string in quotes at the end. Whenever I ask someone why they do that they never have a good answer. Usually something like "I thought it had to be that way".

 

Example:

$query = "SELECT * from tbl ORDER BY " . $sort_field . "";

 

lame

[xyph]

I understand what you're saying.

 

I just notice a lot of people who use single quotes for strings switch to double quotes so their SQL queries can have single-quote string declarations. I was saying, why not simply use double-quotes for your SQL-strings.

[scootstah]

I don't know. Just stuck with me from all those years ago I guess.

[sabinmash]

I think part of his question is also why he couldn't use the POST value directly inside the parens with the forwardslashes such as

"/$_POST['withthis']/"

 

As I am sure you know, you can use variables directly inside a double quoted string. But, when you have an array value with quotes around the key, PHP gets confused. The simple solution is to enclose the variables inside curly braces. I try to do this for ALL my variables within double quoted strings out of habit so I don't have to worry about the scenarios where they would fail.

 

This should work for you.

$new_text = preg_replace("/{$_POST['replacethis']}/" ,$_POST['withthis'],$_POST['text']);

 

Worked like a charm, thanks!