envsubst

envsubst is a Go package for expanding variables in a string using ${var} syntax. Includes support for bash string replacement functions.

Documentation

Documentation can be found on GoDoc.

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

For a deeper reference, see bash-hackers or gnu pattern matching.

Unsupported Functions

• ${var-default}
• ${var+default}
• ${var:?default}
• ${var:+default}