Regular Expressions 101

1st Alternative[1-9]\d{4}

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

\d{4}a digit, repeated exactly 4 times

2nd Alternative0[1-9]\d{3}

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

\d{3}a digit, repeated exactly 3 times

3rd Alternative00[1-9]\d{2}

00the literal text 00

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

\d{2}a digit, repeated exactly 2 times

4th Alternative000[1-9]\d

000the literal text 000

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

\da digit

5th Alternative0000[1-9]

0000the literal text 0000

Character Class[1-9]

1-9one character from 1 (49₁₀) to 9 (57₁₀)

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Regular Expression

[1-9]\d{4}|0[1-9]\d{3}|00[1-9]\d{2}|000[1-9]\d|0000[1-9]

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