Basic HTML version of Foils prepared Sept 20 97

Foil 44 Matched Variables in
Regular Expressions

From Tutorial on PERL Computational Science for Information Age Course CPS616 -- Sept 20 97. by Geoffrey C. Fox,Nancy McCracken,Tom Scavo
The variables \1, \2, \3 etc. correspond to parentheses inside the regex. Outside the regular expression use the PERL variables $1, $2, $3 etc.
In string matching, we identify three parts:
  • $` is variable holding substring BEFORE matched part
  • $& is variable holding substring matched by regular expression
  • $' is variable holding substring AFTER matched part
So original string is the concatenation $` . $& . $'
Note, however, any script that uses these variables suffers a significant performance hit!

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