rgrep.1 -lRE 'errorutil\.Handler' | xargs.1posix sed -i -E 's/Handler\(([A-Za-z0-9_\.]+)\)/Handler(\1, "default value")/'
print lines matching a pattern
-l, --files-with-matches
       Suppress normal output; instead print the name of each input file from which output would normally
       have been printed.  The scanning will stop on the first match.  (-l is specified by POSIX.)
    -R, -r, --recursive
           Read all files under each directory, recursively; this is equivalent to the -d recurse option.

Other Options
    --line-buffered
           Use line buffering on output.  This can cause a performance penalty.
Pipelines
    A  pipeline is a sequence of one or more commands separated by one of the control operators | or |&.  The
    format for a pipeline is:

           [time [-p]] [ ! ] command [ [||&] command2 ... ]

    The standard output of command is connected  via  a  pipe  to  the  standard  input  of  command2.   This
    connection  is performed before any redirections specified by the command (see REDIRECTION below).  If |&
    is used, the standard error of command is connected to command2's standard input through the pipe; it  is
    shorthand  for  2>&1  |.   This  implicit  redirection  of  the  standard  error  is  performed after any
    redirections specified by the command.

    The return status of a pipeline is the exit status of the last command, unless  the  pipefail  option  is
    enabled.   If  pipefail  is  enabled,  the  pipeline's return status is the value of the last (rightmost)
    command to exit with a non-zero status, or zero if all commands exit successfully.  If the reserved  word
    !   precedes  a  pipeline, the exit status of that pipeline is the logical negation of the exit status as
    described above.  The shell waits for all commands in the pipeline to terminate before returning a value.

    If the time reserved word precedes a pipeline, the elapsed as well as user and system  time  consumed  by
    its execution are reported when the pipeline terminates.  The -p option changes the output format to that
    specified by POSIX.  When the shell is in posix mode, it does not recognize time as a  reserved  word  if
    the  next  token begins with a `-'.  The TIMEFORMAT variable may be set to a format string that specifies
    how the timing information should be displayed; see the description of TIMEFORMAT under  Shell  Variables
    below.

    When the shell is in posix mode, time may be followed by a newline.  In this case, the shell displays the
    total user and system time consumed by the shell and its children.  The TIMEFORMAT variable may  be  used
    to specify the format of the time information.

    Each command in a pipeline is executed as a separate process (i.e., in a subshell).
construct argument lists and invoke utility
-E  eofstr
       Use  eofstr  as  the logical end-of-file string. If -E is not specified, it is unspecified whether
       the logical end-of-file string is the underscore character (  '_'  )  or  the  end-of-file  string
       capability  is disabled. When eofstr is the null string, the logical end-of-file string capability
       shall be disabled and underscore characters shall be taken literally.
source manpages: rgrepxargs