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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