UNIX for Beginners Questions & Answers

echo "123 abc" | sed 's/[0-9]*/& www &/'


Output: 
123 www 123 abc

       s/regexp/replacement/
              Attempt to match regexp against the pattern space.  If  success‐
              ful,   replace  that  portion  matched  with  replacement.   The
              replacement may contain the special character & to refer to that
              portion  of  the  pattern  space  which matched, and the special
              escapes \1 through \9 to refer  to  the  corresponding  matching
              sub-expressions in the regexp.

echo "123 abc" | sed 's/[0-9]*/& www &/'