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

Copyright (C) 1987, 1989, 1991 Free Software Foundation, Inc.

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

Bash is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 1, or (at your option) any later
version.

Bash is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License along
with Bash; see the file COPYING.  If not, write to the Free Software
Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

$PRODUCES read.c

$BUILTIN read
$FUNCTION read_builtin
$SHORT_DOC read [-r] [name ...]
One line is read from the standard input, and the first word is
assigned to the first NAME, the second word to the second NAME, etc.
with leftover words assigned to the last NAME.  Only the characters
found in $IFS are recognized as word delimiters.  The return code is
zero, unless end-of-file is encountered.  If the -r option is given,
this signifies `raw' input, and backslash processing is disabled.
$END

#include <stdio.h>
#include "../shell.h"
#include "common.h"

#define issep(c)	(strchr (ifs_chars, (c)) != (char *)0)

static int stream_close ();

extern int interrupt_immediately;

/* Read the value of the shell variables whose names follow.
   The reading is done from the current input stream, whatever
   that may be.  Successive words of the input line are assigned
   to the variables mentioned in LIST.  The last variable in LIST
   gets the remainder of the words on the line.  If no variables
   are mentioned in LIST, then the default variable is $REPLY.

   S. R. Bourne's shell complains if you don't name a variable
   to receive the stuff that is read.  GNU's shell doesn't.  This
   allows you to let the user type random things. */
read_builtin (list)
     WORD_LIST *list;
{
  register char *varname;
  int size, c, i, fildes, raw_mode, pass_next, saw_escape, retval;
  char *input_string, *orig_input_string, *ifs_chars, *t;
  FILE *input_stream;
  SHELL_VAR *var;

  i = 0;		/* Index into the string that we are reading. */
  raw_mode = 0;		/* Not reading raw input be default. */

  while (list)
    {
      if (ISOPTION (list->word->word, 'r'))
	{
	  raw_mode = 1;
	  list = list->next;
	}
      else if (ISOPTION (list->word->word, '-'))
	{
	  list = list->next;
	  break;
	}
      else if (*list->word->word == '-')
	{
	  bad_option (list->word->word);
	  builtin_error ("usage: read [-r] [name ...]");
	  return (EX_USAGE);
	}
      else
	break;
    }

  /* We need unbuffered input from stdin.  So we make a new stream with
     the same file descriptor as stdin, then unbuffer it. */
  fildes = dup (fileno (stdin));

  if (fildes == -1)
    return (EXECUTION_FAILURE);

  input_stream = fdopen (fildes, "r");

  if (!input_stream)
    {
      close (fildes);
      return (EXECUTION_FAILURE);
    }

  var = find_variable ("IFS");
  ifs_chars = var ? value_cell (var) : " \t\n";
  
  input_string = xmalloc (size = 128);

  setbuf (input_stream, (char *)NULL);

  begin_unwind_frame ("read_builtin");
  add_unwind_protect (xfree, input_string);
  add_unwind_protect (stream_close, input_stream);
  interrupt_immediately++;

  pass_next = 0;	/* Non-zero signifies last char was backslash. */
  saw_escape = 0;	/* Non-zero signifies that we saw an escape char */

  while ((c = getc (input_stream)) != EOF)
    {
      if (i + 2 >= size)
	input_string = xrealloc (input_string, size += 128);

      /* If the next character is to be accepted verbatim, a backslash
	 newline pair still disappears from the input. */
      if (pass_next)
	{
	  if (c == '\n')
	    i--;		/* back up over the CTLESC */
	  else
	    input_string[i++] = c;
	  pass_next = 0;
	  continue;
	}

      if (c == '\\' && !raw_mode)
	{
	  pass_next++;
	  saw_escape++;
	  input_string[i++] = CTLESC;
	  continue;
	}

      if (c == '\n')
	break;

      if (c == CTLESC || c == CTLNUL)
	{
	  saw_escape++;
	  input_string[i++] = CTLESC;
	}

      input_string[i++] = c;
    }
  input_string[i] = '\0';

  interrupt_immediately--;
  discard_unwind_frame ("read_builtin");

  fclose (input_stream);

  if (c == EOF)
    {
      retval = EXECUTION_FAILURE;
      /* input_string[0] = '\0'; */
    }
  else
    retval = EXECUTION_SUCCESS;

  if (!list)
    {
      if (saw_escape)
	{
	  t = dequote_string (input_string);
	  var = bind_variable ("REPLY", t);
	  free (t);
	}
      else
	var = bind_variable ("REPLY", input_string);
      var->attributes &= ~att_invisible;
      free (input_string);
    }
  else
    {
      /* This code implements the Posix.2 spec for splitting the words
	 read and assigning them to variables.  If $IFS is unset, we
	 use the default value of " \t\n". */
      orig_input_string = input_string;

      /* Remove IFS white space at the beginning of the input string.  If
	 $IFS is null, no field splitting is performed. */
      for (t = input_string; *ifs_chars && spctabnl (*t) && issep (*t); t++)
	;
      input_string = t;

      for (; list->next; list = list->next)
	{
	  char *e, *t1;

	  varname = list->word->word;
	  if (legal_identifier (varname) == 0)
	    {
	      builtin_error ("%s: not a legal variable name", varname);
	      free (orig_input_string);
	      return (EXECUTION_FAILURE);
	    }

	  /* If there are more variables than words read from the input,
	     the remaining variables are set to the empty string. */
	  if (*input_string)
	    {
	      /* This call updates INPUT_STRING. */
	      t = get_word_from_string (&input_string, ifs_chars, &e);
	      if (t)
		*e = '\0';
	      /* Don't bother to remove the CTLESC unless we added one
		 somewhere while reading the string. */
	      if (t && saw_escape)
		{
		  t1 = dequote_string (t);
		  var = bind_variable (varname, t1);
		  free (t1);
		}
	      else
		var = bind_variable (varname, t);
	    }
	  else
	    {
	      t = (char *)0;
	      var = bind_variable (varname, "");
	    }

	  stupidly_hack_special_variables (varname);
	  var->attributes &= ~att_invisible;

	  if (t)
	    free (t);
	}

      if (legal_identifier (list->word->word) == 0)
	{
	  builtin_error ("%s: not a legal variable name", list->word->word);
	  free (orig_input_string);
	  return (EXECUTION_FAILURE);
	}

      /* This has to be done this way rather than using string_list
	 and list_string because Posix.2 says that the last variable gets the
	 remaining words and their intervening separators. */
      input_string = strip_trailing_ifs_whitespace (input_string, ifs_chars,
						      saw_escape);

      if (saw_escape)
	{
	  t = dequote_string (input_string);
	  var = bind_variable (list->word->word, t);
	  free (t);
	}
      else
	var = bind_variable (list->word->word, input_string);
      stupidly_hack_special_variables (list->word->word);
      var->attributes &= ~att_invisible;
      free (orig_input_string);
    }

  return (retval);
}

/* This way I don't have to know whether fclose () is a
   function or a macro. */
static int
stream_close (file)
     FILE *file;
{
  return (fclose (file));
}