Regular Expressions 101

Explanation

Pro

^start of line

Positive Lookahead(?=[ ]*$|(?![ ]))

1st Alternative[ ]*$

Character Class[ ]*

*matches any number of characters from the set below:

the literal (32₁₀ / 40₈ / 20₁₆)

$end of line

2nd Alternative(?![ ])

Negative Lookahead(?![ ])

Character Class[ ]

the literal (32₁₀ / 40₈ / 20₁₆)

Negative Lookahead(?!.*([!&-]).*(?!\1)[!&-])

.*any character (except for line terminators), repeated any number of times

Group 1([!&-])

Character Class[!&-]

!the literal ! (33₁₀ / 41₈ / 21₁₆)

&the literal & (38₁₀ / 46₈ / 26₁₆)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

.*any character (except for line terminators), repeated any number of times

Negative Lookahead(?!\1)

\1the text saved by group 1

Character Class[!&-]

!the literal ! (33₁₀ / 41₈ / 21₁₆)

&the literal & (38₁₀ / 46₈ / 26₁₆)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

Character Class[a-zA-Z0-9 !&-]{8}

{8}matches exactly 8 characters from the set below:

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

0-9one character from 0 (48₁₀) to 9 (57₁₀)

the literal (32₁₀ / 40₈ / 20₁₆)

!the literal ! (33₁₀ / 41₈ / 21₁₆)

&the literal & (38₁₀ / 46₈ / 26₁₆)

-the literal - (45₁₀ / 55₈ / 2D₁₆)

$end of line

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Detailed match information will be displayed here automatically.

25 tokens

^(?=[ ]*$|(?![ ]))(?!.*([!&-]).*(?!\1)[!&-])[a-zA-Z0-9 !&-]{8}$

New

Legal: 

B-123---
AB&& &&&
A!!!!!!!
B 123---
        

Illegal:

 B-123--
 AB&& &&
B-123!!!
AB&& -
A-&!