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Assertions

Also called anchors or even zero-width assertions, these specify a position in the source text, not any text itself.

  • ^ - match the beginning of the source text.

  • $ - match the end of the source text.

  • \b - match a boundary between word and non-word characters.

Drill

  • Use the pattern ^Re.
  • Now enable the m for multiline option.
  • Can you match a literal . at the end of a line? Try it with and without the m option.
  • Use the pattern the and look closely at all the matches found.
  • Now try \bthe.
  • the\b.
  • \bthe\b.

Practice Exercise

When the m or multiline option is used,

  • ^ matches the absolute beginning of the source text, or any position immediately after a newline.

  • $ matches the very end of the source text, or any position immediately before a newline.

  • \A matches the absolute beginning of the source text.

  • \Z matches the very end of the source text.

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