envsubst

Clone of envsubst. Supports parameter expansion.

usage

envsubst-cli [VARIABLE] ... < INPUT > OUTPUT

semantics

I try to be true to the semantics of the original envsubst which are slightly different from the semantics in a shell. These differences include:

• Most "bad substitutions" are allowed
  • ${} -> ${}
  • ${{foo} -> ${{foo}
• Nested expansions are allowed:
  • export foo=bar ${${foo}} -> ${bar}
  • ...but they only expand at depth=1 ;p

Differences from the original envsubst include:

• Shell builtin variables like $$ and $0 are not supported
• Unset variables throw an error by default (use ${parameter-} or ${parameter+} to ignore unset variables)
• Instead of using SHELL-FORMAT whitelisted variable names are passed as arguments

parameter expansion

The following expansions are supported:

form	set and not null	set but null	unset
${parameter:-word}	substitute parameter	substitute word	substitute word
${parameter-word}	substitute parameter	substitute null	substitute word
${parameter:?[word]}	substitute parameter	error, exit	error, exit
${parameter?[word]}	substitute parameter	substitute null	error, exit
${parameter:+word}	substitute word	substitute null	substitute null
${parameter+word}	substitute word	substitute word	substitute null

testing

chicken-install -test

todo if ur bored

• Escapes
• Inplace
• Add reference tests against envsubst
• Add --posix