What is Asterisk Wildcard (*)?
A special character meaning "every possible value" in a cron expression field.
Definition
The asterisk (*) is the most fundamental cron special character. When placed in any field, it means "match every possible value for this field." For example, * in the hour field means "every hour" (0-23), and * in the day-of-week field means "every day." The expression * * * * * matches every minute of every hour of every day.
Simple Analogy
The asterisk is like saying "any" or "all" — it is a blank check that matches everything in that time slot.
Why It Matters
The asterisk is the most-used and most-misunderstood cron character. It is the default value for any field you want to leave unrestricted. Understanding it prevents the classic mistake of writing * when you mean a specific value.
How to Verify
Read each field left to right and translate * as "every." The expression "*/5 * * * *" reads as "every 5th minute, every hour, every day of month, every month, every day of week." If you see more runs than expected, check if you accidentally left a * where you needed 0.
Common Mistakes
The #1 cron mistake: writing "* 9 * * *" thinking it means "at 9 AM." It actually means "every minute during the 9 AM hour" — 60 executions instead of 1. The correct expression is "0 9 * * *" (minute 0 of hour 9).
Best Practices
When building a new expression, start with "0 0 * * *" (daily at midnight) and modify from there. Never start with "* * * * *" and try to narrow down. For any field you want to restrict, replace the * with a specific value first.
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What is Asterisk Wildcard (*)?
The asterisk (*) is the most fundamental cron special character. When placed in any field, it means "match every possible value for this field." For example, * in the hour field means "every hour" (0-23), and * in the day-of-week field means "every day." The expression * * * * * matches every minute of every hour of every day.
Why does Asterisk Wildcard (*) matter for cron jobs?
The asterisk is the most-used and most-misunderstood cron character. It is the default value for any field you want to leave unrestricted. Understanding it prevents the classic mistake of writing * when you mean a specific value.
What are best practices for Asterisk Wildcard (*)?
When building a new expression, start with "0 0 * * *" (daily at midnight) and modify from there. Never start with "* * * * *" and try to narrow down. For any field you want to restrict, replace the * with a specific value first.
Related Terms
Cron Expression
A string of five fields that defines when a scheduled job should run.
Slash Step (/)
A special character specifying interval/step values — "every Nth" value.
Comma Separator (,)
A special character for specifying a list of discrete values in a cron field.
Hyphen Range (-)
A special character defining a contiguous range of values in a cron field.