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] [-p prompt] [-a array] [-e] [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, and so
on, 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 no NAMEs are supplied, the
line read is stored in the REPLY variable.  If the -r option is given,
this signifies `raw' input, and backslash escaping is disabled.  If
the `-p' option is supplied, the string supplied as an argument is
output without a trailing newline before attempting to read.  If -a is
supplied, the words read are assigned to sequential indices of ARRAY,
starting at zero.  If -e is supplied and the shell is interactive,
readline is used to obtain the line.
$END

#include <config.h>

#include <stdio.h>

#if defined (HAVE_UNISTD_H)
#  include <unistd.h>
#endif

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

#if defined (READLINE)
#include "../bashline.h"
#include <readline/readline.h>
#endif

#define issep(c)	(strchr (ifs_chars, (c)))

extern int interrupt_immediately;

#if defined (READLINE)
static char *edit_line ();
#endif
static SHELL_VAR *bind_read_variable ();

/* 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. */
int
read_builtin (list)
     WORD_LIST *list;
{
  register char *varname;
  int size, i, raw, pass_next, saw_escape, eof, opt, retval, edit;
  char c;
  char *input_string, *orig_input_string, *ifs_chars, *prompt, *arrayname;
  char *e, *t, *t1;
  SHELL_VAR *var;
#if defined (ARRAY_VARS)
  WORD_LIST *alist;
#endif
#if defined (READLINE)
  char *rlbuf;
  int rlind;
#endif

  i = 0;		/* Index into the string that we are reading. */
  raw = edit = 0;	/* Not reading raw input by default. */
  arrayname = prompt = (char *)NULL;

#if defined (READLINE)
  rlbuf = (char *)0;
  rlind = 0;
#endif

  reset_internal_getopt ();
  while ((opt = internal_getopt (list, "erp:a:")) != -1)
    {
      switch (opt)
        {
        case 'r':
	  raw = 1;
	  break;
	case 'p':
	  prompt = list_optarg;
	  break;
	case 'e':
#if defined (READLINE)
	  edit = 1;
#endif
	  break;
#if defined (ARRAY_VARS)
	case 'a':
	  arrayname = list_optarg;
	  break;
#endif
	default:
	  builtin_usage ();
	  return (EX_USAGE);
	}
    }
  list = loptend;

  /* IF IFS is unset, we use the default of " \t\n". */
  var = find_variable ("IFS");
  ifs_chars = var ? value_cell (var) : " \t\n";
  if (ifs_chars == 0)		/* XXX */
    ifs_chars = "";		/* XXX */

  input_string = xmalloc (size = 128);

  begin_unwind_frame ("read_builtin");
  add_unwind_protect (xfree, input_string);
#if defined (READLINE)
  add_unwind_protect (xfree, rlbuf);
#endif
  interrupt_immediately++;

  /* If the -p or -e flags were given, but input is not coming from the
     terminal, turn them off. */
  if ((prompt || edit) && (isatty (0) == 0))
    {
      prompt = (char *)NULL;
      edit = 0;
    }

  if (prompt && edit == 0)
    {
      fprintf (stderr, "%s", prompt);
      fflush (stderr);
    }

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

  for (eof = 0;;)
    {
#if defined (READLINE)
      if (edit)
	{
	  if (rlbuf && rlbuf[rlind] == '\0')
	    {
	      xfree (rlbuf);
	      rlbuf = (char *)0;
	    }
	  if (rlbuf == 0)
	    {
	      rlbuf = edit_line (prompt ? prompt : "");
	      rlind = 0;
	    }
	  if (rlbuf == 0)
	    {
	      eof = 1;
	      break;
	    }
	  c = rlbuf[rlind++];
	}
      else
#endif   
      if (read (0, &c, 1) != 1)
	{
	  eof = 1;
	  break;
	}

      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 == 0)
	{
	  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");

  retval = eof ? EXECUTION_FAILURE : EXECUTION_SUCCESS;

#if defined (ARRAY_VARS)
  /* If -a was given, take the string read, break it into a list of words,
     an assign them to `arrayname' in turn. */
  if (arrayname)
    {
      var = find_variable (arrayname);
      if (var == 0)
        var = make_new_array_variable (arrayname);
      else if (array_p (var) == 0)
        var = convert_var_to_array (var);

      empty_array (array_cell (var));

      alist = list_string (input_string, ifs_chars, 0);
      if (alist)
	{
	  assign_array_var_from_word_list (var, alist);
	  dispose_words (alist);
	}
      xfree (input_string);
      return (retval);
    }
#endif /* ARRAY_VARS */ 

  /* If there are no variables, save the text of the line read to the
     variable $REPLY.  ksh93 strips leading and trailing IFS whitespace,
     so that `read x ; echo "$x"' and `read ; echo "$REPLY"' behave the
     same way, but I believe that the difference in behaviors is useful
     enough to not do it.  Without the bash behavior, there is no way
     to read a line completely without interpretation or modification.
     If you disagree, change the occurrences of `#if 0' to `#if 1' below. */
  if (list == 0)
    {
#if 0
      orig_input_string = input_string;
      for (t = input_string; ifs_chars && *ifs_chars && spctabnl(*t) && issep(*t); t++)
	;
      input_string = t;
      input_string = strip_trailing_ifs_whitespace (input_string, ifs_chars, saw_escape);
#endif

      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;
#if 0
      free (orig_input_string);
#else
      free (input_string);
#endif
      return (retval);
    }

  /* This code implements the Posix.2 spec for splitting the words
     read and assigning them to variables. */
  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 && *ifs_chars && spctabnl(*t) && issep(*t); t++)
    ;
  input_string = t;

  for (; list->next; list = list->next)
    {
      varname = list->word->word;
#if defined (ARRAY_VARS)
      if (legal_identifier (varname) == 0 && valid_array_reference (varname) == 0)
#else
      if (legal_identifier (varname) == 0)
#endif
	{
	  builtin_error ("`%s': not a valid identifier", 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_read_variable (varname, t1);
	      free (t1);
	    }
	  else
	    var = bind_read_variable (varname, t);
	}
      else
	{
	  t = (char *)0;
	  var = bind_read_variable (varname, "");
	}

      FREE (t);
      if (var == 0)
	{
	  free (orig_input_string);
	  return (EXECUTION_FAILURE);
	}

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

  /* Now assign the rest of the line to the last variable argument. */
#if defined (ARRAY_VARS)
  if (legal_identifier (list->word->word) == 0 && valid_array_reference (list->word->word) == 0)
#else
  if (legal_identifier (list->word->word) == 0)
#endif
    {
      builtin_error ("`%s': not a valid identifier", 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_read_variable (list->word->word, t);
      free (t);
    }
  else
    var = bind_read_variable (list->word->word, input_string);
  stupidly_hack_special_variables (list->word->word);
  if (var)
    var->attributes &= ~att_invisible;
  free (orig_input_string);

  return (retval);
}

static SHELL_VAR *
bind_read_variable (name, value)
     char *name, *value;
{
#if defined (ARRAY_VARS)
  if (valid_array_reference (name) == 0)
    {
      if (legal_identifier (name) == 0)
        {
	  builtin_error ("`%s': not a valid identifier", name);
	  return ((SHELL_VAR *)NULL);
        }
      return (bind_variable (name, value));
    }
  else
    return (do_array_element_assignment (name, value));
#else
  return bind_variable (name, value);
#endif
}

#if defined (READLINE)
static char *
edit_line (p)
     char *p;
{
  char *ret;
  int len;

  if (!bash_readline_initialized)
    initialize_readline ();
  ret = readline (p);
  if (ret == 0)
    return ret;
  len = strlen (ret);
  ret = xrealloc (ret, len + 2);
  ret[len++] = '\n';
  ret[len] = '\0';
  return ret;
}
#endif