The sed regular expressions are essentially the same as the grep regular expressions. They are summarized below.

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  matches the beginning of the line
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<td>
  matches the end of the line
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<td>
  Matches any single character
</td>

<td>
  match arbitrarily many occurences of (character)
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<td>
  Match 0 or 1 instance of (character)
</td>

<td>
  Match any character enclosed in [] (in this instance, a b c d e or f)<br /> ranges of characters such as <code>[a-z]</code> are permitted. The behaviour<br /> of this deserves more description. See the page on <a HREF="grep.html">grep</a><br /> for more details about the syntax of lists.
</td>

<td>
  Match any character <em>NOT</em> enclosed in [] (in this instance, any character other than a b c d e or f)
</td>

<td>
  Match m-n repetitions of (character)
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<td>
  Match m or more repetitions of (character)
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<td>
  Match n or less (possibly 0) repetitions of (character)
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<td>
  Match exactly n repetitions of (character)
</td>

<td>
  Group operator.
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<td>
  Backreference - matches nth group
</td>

<td>
  Matches expression1 or expression 2. Works with GNU sed, but this feature might not work with other forms of sed.
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