This file is shift.def, from which is created shift.c.
It implements the builtin "shift" in Bash.

Copyright (C) 1987-2020 Free Software Foundation, Inc.

This file is part of GNU Bash, the Bourne Again SHell.

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it under the terms of the GNU General Public License as published by
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$PRODUCES shift.c

#include <config.h>

#if defined (HAVE_UNISTD_H)
#  ifdef _MINIX
#    include <sys/types.h>
#  endif
#  include <unistd.h>
#endif

#include "../bashansi.h"
#include "../bashintl.h"

#include "../shell.h"
#include "common.h"

$BUILTIN shift
$FUNCTION shift_builtin
$SHORT_DOC shift [n]
Shift positional parameters.

Rename the positional parameters $N+1,$N+2 ... to $1,$2 ...  If N is
not given, it is assumed to be 1.

Exit Status:
Returns success unless N is negative or greater than $#.
$END

int print_shift_error;

/* Shift the arguments ``left''.  Shift DOLLAR_VARS down then take one
   off of REST_OF_ARGS and place it into DOLLAR_VARS[9].  If LIST has
   anything in it, it is a number which says where to start the
   shifting.  Return > 0 if `times' > $#, otherwise 0. */
int
shift_builtin (list)
     WORD_LIST *list;
{
  intmax_t times;
  int itimes, nargs;

  CHECK_HELPOPT (list);

  if (get_numeric_arg (list, 0, &times) == 0)
    return (EXECUTION_FAILURE);

  if (times == 0)
    return (EXECUTION_SUCCESS);
  else if (times < 0)
    {
      sh_erange (list ? list->word->word : NULL, _("shift count"));
      return (EXECUTION_FAILURE);
    }
  nargs = number_of_args ();
  if (times > nargs)
    {
      if (print_shift_error)
	sh_erange (list ? list->word->word : NULL, _("shift count"));
      return (EXECUTION_FAILURE);
    }
  else if (times == nargs)
    clear_dollar_vars ();
  else
    shift_args (itimes = times);

  invalidate_cached_quoted_dollar_at ();

  return (EXECUTION_SUCCESS);
}