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On 03/23/2013 01:44 PM, Alec Warner wrote:
> On Sat, Mar 23, 2013 at 9:26 AM, Michał Górny <[email protected]>
> wrote:
>> + # Close the lock file when we are done
>> with it. + # Prevents deadlock if we aren't
>> in a subshell. + eval "exec ${lock_fd}>&-"
>
> Not following this bit.
>
> The bash manpage says N>&DIGIT- redirects fd DIGIT to fd N. N may
> be unspecified and defaults to 1.
>
> It doesn't say what happens if DIGIT is unspecified. Nor does it
> say it closes any file descriptors.
>
The relevant section of bash(1) is reproduced below:
Duplicating File Descriptors
The redirection operator
[n]<&word
is used to duplicate input file descriptors. If word expands to
one or more digits, the file descriptor denoted by n is made to
be a copy of that file descriptor. If the digits in word do not
specify a file descriptor open for input, a redirection error
occurs. If word evaluates to -, file descriptor n is closed.
If n is not specified, the standard input (file descriptor 0) is
used.
The operator
[n]>&word
is used similarly to duplicate output file descriptors. If n is
not specified, the standard output (file descriptor 1) is used.
If the digits in word do not specify a file descriptor open for
output, a redirection error occurs. As a special case, if n is
omitted, and word does not expand to one or more digits, the
standard output and standard error are redirected as described
previously.
While the outcome of n>&- is not specified directly in the man page,
it is treated exactly as n<&- is.
- --
Jonathan Callen
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