Kleene star

An asterisk repeating the preceding element any number of times.

Also known as: Repetition star, Regex wildcard

Everyday & digitalMathematicalStandard profile

Meanings

In a regular expression the asterisk applies to whatever comes immediately before it, matching that element zero or more times. It is named after Stephen Kleene, who introduced the operation in 1951.

Officially standardisedVerified fact
POSIX defines the asterisk in a regular expression as matching zero or more occurrences of the preceding element.
Contexts: Software
Common modern usageVerified fact
Takes its name from Stephen Kleene's work on regular sets, where the star denotes closure under concatenation.
Contexts: Software

Visual description

A small star of straight strokes radiating from a common centre, placed immediately after the element it repeats.

Symmetry: radial
Orientation: upright

Commonly confused with: Glob wildcard
Both are asterisks in pattern matching with different meanings — the glob star stands for characters, this one repeats what precedes it.
Part of the same system as: Regular expression caret anchor
Both are used in software contexts.

Compare: Glob wildcard vs Kleene star →

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is defined by a current official standard.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references.

Sources

POSIX.1-2024, Regular Expressions
The Open Group / IEEE · retrieved 2026-08-01
Cited for the metacharacters of basic and extended regular expressions. Later dialects (PCRE, ECMAScript) extend this and diverge from it; where a record describes a construct POSIX does not define, it says so and is typed as documented practice.
Regular expression
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for widely-agreed identity, origin and current use, not for contested detail or exact dates.

Last reviewed 2026-08-01

Part of

Regular expression metacharacters

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Meanings

In a regular expression the asterisk applies to whatever comes immediately before it, matching that element zero or more times. It is named after Stephen Kleene, who introduced the operation in 1951.

Officially standardisedVerified fact

POSIX defines the asterisk in a regular expression as matching zero or more occurrences of the preceding element.

Contexts: Software

Common modern usageVerified fact

Takes its name from Stephen Kleene's work on regular sets, where the star denotes closure under concatenation.

Contexts: Software

Related & commonly confused symbols

Commonly confused with: Glob wildcard
Both are asterisks in pattern matching with different meanings — the glob star stands for characters, this one repeats what precedes it.
Part of the same system as: Regular expression caret anchor
Both are used in software contexts.

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is defined by a current official standard.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references.

Sources

POSIX.1-2024, Regular Expressions
The Open Group / IEEE · retrieved 2026-08-01
Cited for the metacharacters of basic and extended regular expressions. Later dialects (PCRE, ECMAScript) extend this and diverge from it; where a record describes a construct POSIX does not define, it says so and is typed as documented practice.
Regular expression
Wikipedia · retrieved 2026-08-01
Tertiary reference. Used for widely-agreed identity, origin and current use, not for contested detail or exact dates.

Last reviewed 2026-08-01