odo - an atomic odometer for the command line
odo [-c | -i | -r | -s COUNT] [-p] file
odo atomically updates a count in a file, which will be created if not present. The count is text-formatted (e.g. "00012345\n"), and will be accurately incremented or reset even when multiple processes attempt to change the counter at the same time. (It uses memory mapping and atomic compare-and-swap operations to eliminate race conditions.)
This could be used to track some intermittent event, like services being restarted. Since the counter is just a number in a text file, it's easy ls to compose odo with other tools.
These options impact how the counter is updated:
-cPrint the current counter value without updating.
-iIncrement the counter. (This is the default.)
-rReset the counter to 0.
-s COUNTUpdate the counter to a specific value.
-pPrint the new value of the counter after updating.
Returns 0 if the counter has been successfully updated. Returns 1 if the file could not be read, created, or written, or if its current contents do not match the expected format of a counter file.
This atomically increments a counter in /log/restarts. If the counter file does not exist, it is created as 0 and incremented to 1.
$ odo /log/restarts
Same, but print the updated count:
$ odo -p /log/restarts
Reset the count to 0:
$ ./odo -r /log/restarts
Set the count to a number (for testing notifications, perhaps):
$ ./odo -s 12345 /log/restarts
Print the current counter value without incrementing:
$ ./odo -c /log/restarts
Print usage / help:
$ ./odo -h
odo's atomicity is only as reliable as the underlying filesystem's. Inconsistencies may still occur if used on a non-local filesystems such as nfs.
odo is Copyright (C) 2014 Scott Vokes scott.vokes@atomicobject.com.
runit(8), sqlite3(1), nfsd(8)