Before the regular expression shown in the study, we need to learn positive expression delimiter is shown.
Delimiter, a boundary is set, that is, the regular expression has been shown within the boundary.
PHP regular expression shown delimiter defined as follows:
Delimiter, you can not use a-zA-Z0-9 \ others can be used. It must be paired with a start there is an end. Marble mechanical components repair
Let cases a few examples:
| example | Explanation |
|---|---|
| / Write regular middle / | correct |
| Middle to write regular $ $ | correct |
| % Intermediate to write regular% | correct |
| ^ ^ Middle to write regular | correct |
| @ @ Middle to write regular | correct |
| (Middle to write regular) | error |
| A middle write regular A | error |
Note: \ is the escape character, if the regular expression shown in the later need to match the inside / below:
/ / /
This time we really want to match / when the need to put inside the delimiter / escape it with the escape character, written in the following example:
/ \/ /
If you do not bother to meet this need the escape character when you can put two forward slashes (/ /) delimited, instead of the other delimiters (##).