>perl -wMstrict -le
"use YAPE::Regex::Explain;
 ;;
 my $rx = qr/^update\ (\w*)[^\s]/;
 print YAPE::Regex::Explain->new($rx)->explain;
"
The regular expression:

(?-imsx:^update\ (\w*)[^\s])

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  update                   'update'
----------------------------------------------------------------------
  \                        ' '
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    \w*                      word characters (a-z, A-Z, 0-9, _) (0 or
                             more times (matching the most amount
                             possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  [^\s]                    any character except: whitespace (\n, \r,
                           \t, \f, and " ")
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------