If you have a cadence sensor on your bike such as the Garmin GSC-10, you can approximate the number of pedal turns you made on the bike ride using the following script (requires GPSBabel):
#!/bin/sh STYLE="$(mktemp)" cat >${STYLE} <<EOF FIELD_DELIMITER COMMA RECORD_DELIMITER NEWLINE OFIELD CADENCE,"","%d" EOF exec gpsbabel -i garmin_fit -f "${1}" -o xcsv,style=${STYLE} -F- | awk '{x += $1} END {print int(x / 60)}'
... then call with:
$ sh cadence.sh ~/path/to/2014-11-16-14-46-05.fit
24344
Unfortunately the Garmin .fit format doesn't store the actual number of pedal turns, only the average for each particular second. However, it should be reasonably accurate given that one keeps a reasonably steady cadence.
As a bonus, using a small amount of shell plumbing you can then sum an entire year's worth of riding like so:
$ for X in ~/path/to/2014-*.fit; do sh cadence.sh ${X}; done | awk '{x += $1} END { print x }' 749943