There are multiple issues here:
- First, your console queries work fine in MongoDB v2.0.2 but don't work in MongoDB v2.2.1. This is probably a regression bug, but the JavaScript parser may have intentionally been changed between versions. The
... after entering a command means the console is waiting for a multi-line command to be completed; I'm not sure why in this specific situation.
- Also, the backslash character
\ in the $regex string must itself be escaped. (The JavaScript parser consumes the escape first, before the regex engine gets to see it.)
> db.test.find({word:{$regex:"\["}}); // no result
> db.test.find({word:{$regex:"\\["}}); // returns result when escaped properly
{ "_id" : 0, "word" : "[" }
{ "_id" : 1, "word" : "[]" }
MongoDB 2.0.2 console output:
> db.test.drop(); version()
version: 2.0.2
>
> db.test.insert({_id: 0, word: '['});
> db.test.insert({_id: 1, word: '[]'});
> db.test.insert({_id: 2, word: ']'});
> db.test.insert({_id: 9, word: 'no brackets'});
>
> db.test.find({word:/[\[]/}); // could not be run in console
{ "_id" : 0, "word" : "[" }
{ "_id" : 1, "word" : "[]" }
> db.test.find({word:/\[/ }); // could not be run in console
{ "_id" : 0, "word" : "[" }
{ "_id" : 1, "word" : "[]" }
> db.test.find({word:/\]/}); //returns result
{ "_id" : 1, "word" : "[]" }
{ "_id" : 2, "word" : "]" }
> db.test.find({word:/[\]]/}); //returns result
{ "_id" : 1, "word" : "[]" }
{ "_id" : 2, "word" : "]" }
> db.test.find({word:{$regex:"\["}}); //no result
> db.test.find({word:{$regex:"\\["}}); //returns result when escaped properly
{ "_id" : 0, "word" : "[" }
{ "_id" : 1, "word" : "[]" }
> db.test.find({word:{$regex:"\[[]"}}); //returns result
{ "_id" : 0, "word" : "[" }
{ "_id" : 1, "word" : "[]" }
MongoDB 2.2.1 console output:
> db.test.drop(); version()
version: 2.2.1
>
> db.test.insert({_id: 0, word: '['});
> db.test.insert({_id: 1, word: '[]'});
> db.test.insert({_id: 2, word: ']'});
> db.test.insert({_id: 9, word: 'no brackets'});
>
> db.test.find({word:/[\[]/}); // could not be run in console
... db.test.find({word:/\[/ }); // could not be run in console
... db.test.find({word:/\]/}); // returns result
... db.test.find({word:/[\]]/}); // returns result
{ "_id" : 1, "word" : "[]" }
{ "_id" : 2, "word" : "]" }
> db.test.find({word:{$regex:"\["}}); // no result
> db.test.find({word:{$regex:"\\["}}); // returns result when escaped properly
{ "_id" : 0, "word" : "[" }
{ "_id" : 1, "word" : "[]" }
> db.test.find({word:{$regex:"\[[]"}}); // returns result
MongoDB 2.2.1 console output (commented out lines that don't parse as expected):
> db.test.drop(); version()
version: 2.2.1
>
> db.test.insert({_id: 0, word: '['});
> db.test.insert({_id: 1, word: '[]'});
> db.test.insert({_id: 2, word: ']'});
> db.test.insert({_id: 9, word: 'no brackets'});
>
> // db.test.find({word:/[\[]/}); // could not be run in console
> // db.test.find({word:/\[/ }); // could not be run in console
> db.test.find({word:/\]/}); // returns result
{ "_id" : 1, "word" : "[]" }
{ "_id" : 2, "word" : "]" }
> db.test.find({word:/[\]]/}); // returns result
{ "_id" : 1, "word" : "[]" }
{ "_id" : 2, "word" : "]" }
> db.test.find({word:{$regex:"\["}}); // no result
> db.test.find({word:{$regex:"\\["}}); // returns result when escaped properly
{ "_id" : 0, "word" : "[" }
{ "_id" : 1, "word" : "[]" }
> db.test.find({word:{$regex:"\[[]"}}); // returns result
{ "_id" : 0, "word" : "[" }
{ "_id" : 1, "word" : "[]" }
>
