What is wrong with this code?

teguh123

$Query404=preg_replace("[/\-]"," ",$Query404);//bad escape sequence - do you mean \-

$Query404=preg_replace("'[\_]'i"," ",$Query404);//bad escape sequence \_ do you mean \\_

Zend put warning

laserlight

The problem is that "\-" can be read as: two backslashes that represent a single backslash, then a backslash followed by a dash... hold on, that's an invalid escape sequence. It so happens that when an invalid escape sequence is found it is treated like it is not an escape sequence (i.e., two characters rather than one), but this can be confusing.

As such, to clarify you should either escape that third backslash, or remove it if it is a mistake.

By the way, I suggest using single quoted strings for regex patterns as it avoids various other escape sequences.

teguh123

What I mean by \- is either \ (hence \) or - (hence -) should be turned into space. Changing it using ' doesnt work.

Why is "" is different than ' in escaping regular expression?

laserlight

teguh123 wrote:
Why is "" is different than ' in escaping regular expression?

It is different with respect to PHP. The problem is that there are two levels of interpretation at work here. At one level, the string is interpreted according to the rules for strings in PHP. At the next level, the interpreted PHP string is then interpreted as a regular expression pattern.

Single quoted PHP strings have fewer escape sequences, hence it is easier to work with them when you have these two levels of interpretation. Unfortunately, \ is an escape sequence for single quoted strings as well, so using them in this specific pattern does not make a difference.

teguh123 wrote:
What I mean by \- is either \ (hence \) or - (hence -) should be turned into space.

To express a backslash in a regex pattern, you usually need to escape it with a backslash. To express a backslash in a PHP string, you also usually need to escape it with a backslash. Therefore, you should write '\\' to express a backslash.

Based on what you stated, the preceding forward slash should not be there. Therefore, you should write:

$Query404 = preg_replace('[\\\\-?]', ' ', $Query404);