On 03/22/2018 05:47 PM, Jorgen Harmse wrote:
I see Eric's point, but it seems to me that my use case is not unusual. (Rename
a file unless the target exists, in which case check that they are the same
before removing one.) Perhaps the documentation of mv could suggest a solution,
e.g.
(ls b &> /dev/null && diff a b > /dev/null && rm a) || mv -n a b
That's a TOCTTOU race.
It sounds like what you want is close to the kernel's
renameat2(,RENAME_NOREPLACE) semantics, which atomically renames a file
or fails if the destination already exists, then on failure check if the
two files are identical before removing the source.
I don't know if mv exposes RENAME_NOREPLACE semantics yet, but it should
be taught to do so, where such semantics are available.
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