Differential D28071
cmp: fix -s (silent) when used with skip offsets Authored by emaste on Jan 9 2021, 10:02 PM. Tags None Referenced Files
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Details -s causes cmp to print nothing for differing files, for use when only the exit status is of interest. -z compares the file size first, for regular files, and fails the comparison early if they do not match. Prior to this change -s implied -z as an optimization, but this is not valid when file offsets are specified. Now, enable the -z optimization for -s only if both skip arguments are not provided / 0. PR: 252542
Diff Detail
Event TimelineComment Actions -z basically ignores user-specified file offsets: echo -n '1234567890' > a echo -n 'abc567890' > b cmp -z a b 4 3 => a and b differ I'm not sure if it's really a bug or not (if not some clarification in the man page would be good), but in principle you could retain the optimization if -z instead checks for size1 - skip1 != size2 - skip2. Comment Actions
Agreed, the documentation is not quite clear on this although the code matches the interpretation I would take from the man page. It's probably worth changing the optimization as you suggest, and making this explicit in the man page... I might take a look at it later. |