4.4.2 Replacement expressions

For the replacement expression, following characters have special meanings:

• &

  • This represents what the regular expression matched. (use \& in emacs)

• \n

  • This represents what the n-th bracketed regular expression matched.

For Perl replacement string, $n is used instead of \n and & has no special meaning.

For example:

     $ echo zzz1abc2efg3hij4 | \
       sed -e 's/\(1[a-z]*\)[0-9]*\(.*\)$/=&=/'
     zzz=1abc2efg3hij4=
     $ echo zzz1abc2efg3hij4 | \
       sed -e 's/\(1[a-z]*\)[0-9]*\(.*\)$/\2===\1/'
     zzzefg3hij4===1abc
     $ echo zzz1abc2efg3hij4 | \
       perl -pe 's/(1[a-z]*)[0-9]*(.*)$/$2===$1/'
     zzzefg3hij4===1abc
     $ echo zzz1abc2efg3hij4 | \
       perl -pe 's/(1[a-z]*)[0-9]*(.*)$/=&=/'
     zzz=&=

Here please pay extra attention to the style of the bracketed regular expression and how the matched strings are used in the text replacement process on different tools.

These regular expressions can be used for the cursor movements and the text replacement actions in the editors too.

Please read all the related manual pages to learn these commands.