Regular Expressions containing square brackets [ ]

[hsriat]

I need to compare a string with a regular expression that contains square brackets in itself.

eg. If I test() a regExp ("^[b]", "i") with string "[b]Bold Text[/b]", it should return true. But its returning false due to square brackets.
How can I solve this?

[code=javascript]var txt = "[b]Page starts[/b]";
function matchTag(start) {
var regStart = new RegExp("^["+start+"]", "i");
if (regStart.test( txt))
alert ('Matching');
}[/code]

[acoder]

Square brackets are special characters in regular expressions, so you will need to escape them.

[hsriat]

Square brackets are special characters in regular expressions, so you will need to escape them.

oops... how could I miss using escape().

Thanks, I got it working. :)

[code=javascript]var txt = "[b]Page starts[/b]";
function matchTag(start) {
var regStart = new RegExp("^"+esca pe("["+start+"]"), "i");
if (regStart.test( escape(txt)))
alert ('Matching');
}[/code]

[acoder]

Yes, or just the escape character (backslash).

[hsriat]

Yes, or just the escape character (backslash).

Are you talking about this?
[code=javascript]var txt = "[b]Page starts[/b]";
function matchTag(start) {
var regStart = new RegExp("^\["+start+"\]", "i");
if (regStart.test( txt))
alert ('Matching');
}[/code]

This isn't working.

[mrhoo]

To include the literal escape in a string
you have to escape the escape- "\\["

var regStart = new RegExp("^\\["+start+"\\]", "i")

[hsriat]

To include the literal escape in a string
you have to escape the escape- "\\["

var regStart = new RegExp("^\\["+start+"\\]", "i")

Well, thats working, and saved me from lots of escape()s and unescape()s later in the code.
Thank you :)

But I could not get the reason for escaping the backslash for second time escaping. When did it require to escape it second time in the process?

[mrhoo]

A regular expression uses the slash to escape special characters-

var rx=/^\[(\w+)\]/

but strings in javascript escape characters using the same slash

alert('\[') returns the '[', because [ is not a special character in a string.

alert('\\[') returns '\[' because the first slash escaped the second- the slash is a special character in strings.

You will mostly run into it when you create regular expressions from strings,

[hsriat]

Okey... got it now.

Thanks for the explanation :)

Regards,
Harpreet