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_Expressions_

# Regular expressions

The `=~` and `!~` operators can be used to check against regular expressions.

The expression `a =~ b` is true if `a` matches `b`, while
`a !~ b` is true if `a` does _not_ match `b`.

Just as with comparison operators, these operators may be used
as unary versions to define a set of strings.


<!-- CUE editor -->
_regexp.cue:_
```
a: "foo bar" =~ "foo [a-z]{3}"
b: "maze" !~ "^[a-z]{3}$"

c: =~"^[a-z]{3}$" // any string with lowercase ASCII of length 3

d: c
d: "foo"

e: c
e: "foo bar"
```

<!-- result -->
`$ cue eval -i regexp.cue`
```
a: true
b: true
c: =~"^[a-z]{3}$"
d: "foo"
e: _|_ /* invalid value "foo bar" (does not match =~"^[a-z]{3}$") */
```