\1 refers to the match of the first group : Regexps Group « Development « Ruby

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Ruby » Development » Regexps Group 
\1 refers to the match of the first group

# \the second group,and so on.

# Outside the pattern,the special variables $1, $2, and so on, serve the samepurpose. 

"12:50am" =~ /(\d\d):(\d\d)(..)/ # 
"Hour is #$1, minute #$2" "Hour is 12, minute 50" 
"12:50am" =~ /((\d\d):(\d\d))(..)/ # 
"Time is #$1" "Time is 12:50" 
"Hour is #$2, minute #$3" "Hour is 12, minute 50" 
"AM/PM is #$4" "AM/PM is am" 

 
Related examples in the same category
1. An unescaped vertical bar(|) matches either the regular expression that precedes it or the regular expression that follows it.
2. use parentheses to group terms within a regular expression
3. unescape HTML
4. Backslash Sequences in the Substitution
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