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Re^3: read file line by line then do something and write to same file

by oiskuu (Pilgrim)
on Jun 16, 2014 at 19:36 UTC ( #1090066=note: print w/ replies, xml ) Need Help??


in reply to Re^2: read file line by line then do something and write to same file
in thread read file line by line then do something and write to same file

A cursory strace perl -pi reveals a more sloppy pattern than described, however. I see open/unlink/open/read+write/close/close. The unlinked source file is still readable; it gets released upon close.

A relatively safe update sequence is: mkstemp/read+write/fsync/rename. The final rename is atomic, but that itself does not prevent races with multiple updaters (of course).


Comment on Re^3: read file line by line then do something and write to same file
Re^4: read file line by line then do something and write to same file
by davido (Archbishop) on Jun 16, 2014 at 19:44 UTC

    Yes, I believe you're correct regarding the strace. I recall now that the documentation is not 100% truthful as to what is happening behind the scenes. If you use -i.bak instead of -i, you'll probably see an open/rename/open/read+write/close/close instead of open/unlink...


    Dave

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