Re: Redirecting to a stream number held in a variable

[Mark Hobley]

--- On Tue, 29/12/09, Eric Blake <address@hidden> wrote:

> From: Eric Blake <address@hidden>
> Subject: Re: Redirecting to a stream number held in a variable

> You'll have to demonstrate an instance of the bug in
> context, first.

Here is what I have so far:

In an empty directory create a configure.ac file as follows:

#                                               -*- Autoconf -*-
# Process this file with autoconf to produce a configure script.

AC_PREREQ([2.64])
AC_INIT([FULL-PACKAGE-NAME], [VERSION], [BUG-REPORT-ADDRESS])

# Checks for programs.

# Checks for libraries.

# Checks for header files.

# Checks for typedefs, structures, and compiler characteristics.

# Checks for library functions.

AC_OUTPUT

Now run:

autoconf

Using an editor examine the file configure and search for &$

The problematic line appears in the function as_fn_error as follows:

as_fn_error ()
{
  as_status=$?; test $as_status -eq 0 && as_status=1
  if test "$3"; then
    as_lineno=${as_lineno-"$2"} as_lineno_stack=as_lineno_stack=$as_lineno_stack
    $as_echo "$as_me:${as_lineno-$LINENO}: error: $1" >&$3
  fi
  $as_echo "$as_me: error: $1" >&2
  as_fn_exit $as_status
} # as_fn_error

Modify the script to populate $3 with a value of 5 and call as_fn_error()

An error will occur as a result of the >&$3 syntax being used.

This error may occur in real circumstances because $3 is being set to a value 
of 5 as part of the LOG_FD

I found this snipped of code elsewhere in the configure file:

 # Handling of arguments.
for ac_config_target in $ac_config_targets
do
  case $ac_config_target in

  *) as_fn_error "invalid argument: \`$ac_config_target'" "$LINENO" 5;;
  esac
done

Note the number 5. I reckon this may trip the error when the handler runs.

I think that the shells are tripping up on the >&$3 syntax **before** the
substitution to a value is being made.

Mark.