CODEWITHSUNDEEP
linuxshellunix
peedee
peedee

Reputation: 2031

Shell script to nullify a file everytime it reaches a specific size

I am in the middle of writing a shell script to nullify/truncate a file if it reaches certain size. Also the file is being opened/written by a process all the time. Now every time when I nullify the file, will the file pointer be repositioned to the start of the file or will it remain in its previous position? Let me know if we could reset the file pointer once the file has been truncated?

Upvotes: 0

Views: 1827

Answers (2)

user197292
user197292

Reputation: 361

A cron job or something like this will do the task; it will find every files bigger than 4096bytes then nullified the files

$ find -type f -size 4096c -print0 | while IFS= read -r -d $'\0' line; do cat /dev/null > $line; done

enter link description here

Upvotes: 0

Jonathan Leffler
Jonathan Leffler

Reputation: 753675

The position of the file pointer depends on how the file was opened by the process that has it open. If it was opened in append mode, then truncating the file will mean that new data will be written at the end of the file, which is actually the beginning too the first time it writes after the file is truncated. If it was not opened in append mode, then truncating the file will simply mean that there is a series of virtual zero bytes at the start of the file, but the real data will continue to be written at the same point as the last write finished. If the file is being reopened by the other process, rather than being held open, then roughly the same rules apply, but there is a better chance that the file will be written at the beginning. It all depends on how the first process to write to the file after the truncation is managing its file pointer.

You can't reset the file pointer of another process, AFAIK.

Upvotes: 2

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