envsubst

README

Envsubst

Expands variables in a string using ${var} syntax.

Supported Functions

Expression	Meaning
${var}	Value of $var
${#var}	String length of $var
${var^}	Uppercase first character of $var
${var^^}	Uppercase all characters in $var
${var,}	Lowercase first character of $var
${var,,}	Lowercase all characters in $var
${var:n}	Offset $var n characters from start
${var:n:len}	Offset $var n characters with max length of len
${var#pattern}	Strip shortest pattern match from start
${var##pattern}	Strip longest pattern match from start
${var%pattern}	Strip shortest pattern match from end
${var%%pattern}	Strip longest pattern match from end
${var-default	If $var is not set, evaluate expression as $default
${var:-default	If $var is not set or is empty, evaluate expression as $default
${var=default	If $var is not set, evaluate expression as $default
${var:=default	If $var is not set or is empty, evaluate expression as $default
${var/pattern/replacement}	Replace as few pattern matches as possible with replacement
${var//pattern/replacement}	Replace as many pattern matches as possible with replacement
${var/#pattern/replacement}	Replace pattern match with replacement from $var start
${var/%pattern/replacement}	Replace pattern match with replacement from $var end

Skip expansion with a ! prefix.

Expression	Substitution
${HOME}	/home/user
${!HOME}	${HOME}
${UNSET:-default}	default
${!UNSET:-default}	${UNSET:-default}

Documentation

Index

• func Eval(s string, mapping func(string) string) (string, error)
• func EvalEnv(s string) (string, error)
• type Template
  • func Parse(s string) (t *Template, err error)
  • func ParseFile(path string) (*Template, error)
  • func (t *Template) Execute(mapping func(string) string) (str string, err error)

Functions

func Eval

func Eval(s string, mapping func(string) string) (string, error)

Eval replaces ${var} in the string based on the mapping function.

func EvalEnv

func EvalEnv(s string) (string, error)

EvalEnv replaces ${var} in the string according to the values of the current environment variables. References to undefined variables are replaced by the empty string.

Types

type Template

type Template struct {
	// contains filtered or unexported fields
}

Template is the representation of a parsed shell format string.

func Parse

func Parse(s string) (t *Template, err error)

Parse creates a new shell format template and parses the template definition from string s.

func ParseFile

func ParseFile(path string) (*Template, error)

ParseFile creates a new shell format template and parses the template definition from the named file.

func (*Template) Execute

func (t *Template) Execute(mapping func(string) string) (str string, err error)

Execute applies a parsed template to the specified data mapping.