Info Catalog sed: sed regular expressions sed: BRE vs ERE

sed: Regular Expressions Overview

 
 5.1 Overview of regular expression in 'sed'
 ===========================================
 
 To know how to use 'sed', people should understand regular expressions
 ("regexp" for short).  A regular expression is a pattern that is matched
 against a subject string from left to right.  Most characters are
 "ordinary": they stand for themselves in a pattern, and match the
 corresponding characters.  Regular expressions in 'sed' are specified
 between two slashes.
 
    The following command prints lines containing the word 'hello':
 
      sed -n '/hello/p'
 
    The above example is equivalent to this 'grep' command:
 
      grep 'hello'
 
    The power of regular expressions comes from the ability to include
 alternatives and repetitions in the pattern.  These are encoded in the
 pattern by the use of "special characters", which do not stand for
 themselves but instead are interpreted in some special way.
 
    The character '^' (caret) in a regular expression matches the
 beginning of the line.  The character '.' (dot) matches any single
 character.  The following 'sed' command matches and prints lines which
 start with the letter 'b', followed by any single character, followed by
 the letter 'd':
 
      $ printf "%s\n" abode bad bed bit bid byte body | sed -n '/^b.d/p'
      bad
      bed
      bid
      body
 
    The following sections explain the meaning and usage of special
 characters in regular expressions.
 

Info Catalog sed: sed regular expressions sed: BRE vs ERE