envsubst

This is a fork of https://github.com/dnitsch/envsubst where the NoReplace restriction has been added.

This fork improves the NoReplace restriction by not replacing env variables defined with the default like this:

For this input:

ExistingEnvVarIsReplaced: $REPLACE
NoReplaceNotToBeUsedWithDefault: ${someVarWithDefault:=myDefault}
NoReplaceShouldNotReplaceNonExistingEnvVar: $ToIgnore

With these env vars set:

REPLACE=bar

Expected output is:

ExistingEnvVarIsReplaced: bar
NoReplaceNotToBeUsedWithDefault: myDefault
NoReplaceShouldNotReplaceNonExistingEnvVar: $ToIgnore