increment a value pulled from a file I have a cron that I am writing that will repeat every hour, and I need a simple way to pass a counter from the last run to the next run. My plan was to add the number to a file at the end, and then call it back at the beginning, e.g. At end of the first cron run: INC_COUNT=1 echo $INC_COUNT > inc_counter.txt Then at the start of the second run: INC_COUNT_FILE="inc_counter.txt" OLD_INC_COUNTER=$(cat "$INC_COUNT_FILE") So far so good, but now I need to increment that number. I tried: NEW_INC_COUNTER="$OLD_INC_COUNTER"+1 NEW_INC_COUNTER="$OLD_INC_COUNTER+1" neither of which worked. What is the best way to increment this number?

The following methods will work:

1. `NEW_INC_COUNTER=$((OLD_INC_Counter+1))`
2. `((NEW_INC_COUNTER = OLD_INC_Counter+1))`
3. `((OLD_INC_Counter+=1))`
4. `((OLD_INC_Counter++))`
5. `let "NEW_INC_COUNTER = OLD_INC_Counter+1"`
6. `let "OLD_INC_Counter+=1"`
7. `let "OLD_INC_Counter++"`



**Good luck!**