Output redirection to block-defined filehandle

[Martin Langhoff <martin.langhoff@xxxxxxxxx>]

The flock binary in modern linuxes (from util-linux-ng) supports
flocking a filehandle that is handled by the shell. Combining this
with per-code-block filehandles / io redirection, it is an incredibly
useful construct to protect a code block with a lock.

The resulting code looks like this (from man flock on Fedora 11):

      (
         flock -s 200
         # ... commands executed under lock ...
       ) 200>/var/lock/mylockfile

I am now discovering that this works in bash, but not in dash.

Is there a posixly correct way to do this? Can dash handle it? Is
there a syntax for this that is both dash and bash friendly?

If the answer is not -- this codepath is conditional. Is there a way
for me to test for which shell is running (and only attempt it under
bash)?

thanks!


martin
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