Other Resources:
Backreferences \g1, \g2, ...
What is a backreference? How to use a backreference?
How to write a regular expression using a backreferences to capture 5-letter reversible words in a text string like this: civic, level, radar, rotor or stats?
✍: FYIcenter.com
Backreferences are references representing catured sub strings already matched in earlier groups. Backreferences are expressed as \g1, \g2, ... with \g1 referring the sub string resulted from the first group. For example:
(\w+)\s+\g1 # match the same word repeated
The regular expression to match 5-letter reversible words is:
(\w)(\w)\w\g2\g1
(\w) - matches the first letter and capture it as the first group
(\w) - matches the second letter and capture it as the second group
\w - matches the third letter
\g2 - the fourth letter must match the second group result
\g1 - the fifth letter must match the first group result
2013-01-23, 0👍, 0💬
Popular Posts:
According to the IEEE 802 specification, a MAC address has 6 groups of 2 hexadecimal digits separate...
How to write a regular expression to parse key-value entries from Windows .INI files? Here is an exa...
According to the IEEE 802 specification, a MAC address has 6 groups of 2 hexadecimal digits separate...
According to the IEEE 802 specification, a MAC address has 6 groups of 2 hexadecimal digits separate...
How to capture the Baidu spider entries from Web log file? Here are some Web log file entries: 127.0...