Cron表达式相似性判定与特定交替调度表达式构建问询

Are the three Cron expressions similar? Which are redundant? #

All three expressions are identical in their execution behavior—they’ll trigger at 15, 35, and 55 minutes past every hour, every day, no exceptions. Here’s the breakdown:

• Expression a: 15,35,55 * * * *
  The hour field uses *, which means "every hour" (0 through 23).

• Expression b: 15,35,55 */1 * * *
*/1 in the hour field translates to "every 1 hour starting from the first valid hour (0)". This is functionally the same as * because stepping by 1 over the full 0-23 hour range covers every hour.

• Expression c: 15,35,55 0/1 * * *
0/1 means "start at hour 0, increment by 1 each time". This also covers every hour from 0 to 23, matching the behavior of * and */1.

Since all three do exactly the same thing, expressions b and c are redundant compared to a. Expression a is the most concise and standard way to write this schedule.

Custom Cron Schedule for the Desired Pattern #

Your requested schedule follows a repeating rhythm:

• Even-numbered hours (8, 10, 12, ..., 22): Trigger at 35 minutes past the hour
• Odd-numbered hours (9, 11, 13, ..., 23): Trigger at 15 and 55 minutes past the hour

Standard Unix Cron doesn’t support conditional logic (like "if hour is even, use this minute; else use those minutes") in a single expression. The cleanest, most compatible solution is to use two separate Cron expressions:

1. For even hours (runs at 35 past every even hour):

   35 */2 * * *
   

   • */2 in the hour field selects every 2nd hour starting from 0 (so 0, 2, 4, ..., 22—all even hours).

2. For odd hours (runs at 15 and 55 past every odd hour):

   15,55 1-23/2 * * *
   

   • 1-23/2 in the hour field selects every 2nd hour starting from 1 (so 1, 3, 5, ..., 23—all odd hours).

If you’re using a Cron implementation with advanced syntax (like Quartz), you could combine these into one expression with logical OR, but the two-expression approach works with all standard Cron systems and is easier to read/maintain.

内容的提问来源于stack exchange，提问作者rethabile