grep.1posix -lRE 'errorutil\.Handler' | xargs(1) sed(1) -i -E 's/Handler\(([A-Za-z0-9_\.]+)\)/Handler(\1, "default value")/'
search a file for a pattern
-l     (The letter ell.) Write only the names of files containing  selected  lines  to  standard  output.
       Pathnames  shall  be written once per file searched. If the standard input is searched, a pathname
       of "(standard input)" shall be written, in the POSIX locale. In other  locales,  "standard  input"
       may be replaced by something more appropriate in those locales.
-E     Match using extended regular expressions. Treat each pattern specified as an ERE, as described  in
       the  Base  Definitions  volume of IEEE Std 1003.1-2001, Section 9.4, Extended Regular Expressions.
       If any entire ERE pattern matches some part of an input line excluding the terminating  <newline>,
       the line shall be matched.  A null ERE shall match every line.
    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

    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).
build and execute command lines from standard input
stream editor for filtering and transforming text
-i[SUFFIX], --in-place[=SUFFIX]

       edit files in place (makes backup if extension supplied)
If no -e, --expression, -f, or --file option is given, then the first non-option argument is taken as the
sed script to interpret.  All remaining arguments are names  of  input  files;  if  no  input  files  are
specified, then the standard input is read.
source manpages: grepxargssed