Documentation

Work with regular expression types

A regular expression type represents a regular expression pattern.

Type name: regexp

Regular expression syntax

Flux uses the Go regexp implementation and syntax. This syntax is similar to regular expressions in Perl, Python, and other languages. Regular expression literals are enclosed in forward slash characters (/).

/^[a-z0-9]{1,}$/

Use regular expression flags

Flux supports the following regular expression flags:

FlagDescription
icase-insensitive
mmulti-line mode: ^ and $ match begin/end line in addition to begin/end text
slet . match \n
Uungreedy: swap meaning of x* and x*?, x+ and x+?, etc

Include regular expression flags at the beginning of your regular expression pattern enclosed in parentheses (()) and preceded by a question mark (?).

/(?iU)foo*/

Use regular expressions in predicate expressions

To use regular expressions in predicate expressions, use the =~ and !~ comparison operators. The right operand must be a string. The left operand must be a regular expression.

"abc" =~ /\w/
// Returns true

"z09se89" =~ /^[a-z0-9]{7}$/
// Returns true

"foo" !~ /^f/
// Returns false

"FOO" =~ /(?i)foo/
// Returns true

Convert a string to a regular expression

  1. Import the regexp package.
  2. Use regexp.compile() to compile a string into a regular expression type.
import "regexp"

regexp.compile(v: "^- [a-z0-9]{7}")
// Returns ^- [a-z0-9]{7} (regexp type)

Examples

Replace all substrings that match a regular expression

  1. Import the regexp package.

  2. Use regexp.replaceAllString() and provide the following parameters:

    • r: regular expression
    • v: string to search
    • t: replacement for matches to r.
import "regexp"

regexp.replaceAllString(
  r: /a(x*)b/,
  v: "-ab-axxb-",
  t: "T"
)
// Returns "-T-T-"

Return the first regular expression match in a string

  1. Import the regexp package.

  2. Use regexp.findString() to return the first regular expression match in a string. Provide the following parameters:

    • r: regular expression
    • v: string to search
import "regexp"

regexp.findString(
  r: /foo.?/,
  v: "seafood fool"
)
// Returns "food"

Escape regular expression metacharacters in a string

If a string contains regular expression metacharacters that should be evaluated as literal characters, escape the metacharacters before converting the string to a regular expression:

  1. Import the regexp package.
  2. Use regexp.quoteMeta() and provide the string to escape regular expression metacharacters in:
import "regexp"

regexp.quoteMeta(v: ".+*?()|[]{}^$")
// Returns "\.\+\*\?\(\)\|\[\]\{\}\^\$"

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