Environment Variables

When Idio starts, all environment variables are instantiated as variables with dynamic scope, tagged as environ and referencing strings. A small number, PATH, HOME etc., will be set if no such value exists in the initial environment.

You manipulate environment variables as normal variables, they’re just strings.

Whenever an external command is about to be launched a new environment is calculated from the set of variables in scope tagged as environ variables.

simple-env.idio

;; USER is a variable so we'll get everything with my login id in it
env | grep USER

puts "\nTry again\n\n"

;; grep will now be passed the string USER as an argument
env | grep 'USER

$ idio simple-env
...
PATH=/home/idf/.local/bin:...
HOME=/home/idf
LOGNAME=idf
PWD=/home/idf/src/idio.git
USER=idf
_=/home/idf/.local/bin/idio
OLDPWD=/home/idf
IDIOLIB=/home/idf/.local/lib/idio/0.3
...

Try again

USER=idf

Extending the Environment

You can create a new environment variable with the :* operator (cf. the := operator for lexical variables).

If you use :* at the top level (ie. outside of a block) then it is a regular environment variable like any other.

Inside a block, though, these definitions become transient with a lifetime to the end of the block.

For new environment variables this works as you would expect. For existing environment variables, this new definition shadows the existing one (for the lifetime of the block).

Finally, in a block, !* will transiently unset an existing environment variable.

extend-env.idio

define (reporter msg) {
  puts msg
  (newline)
  if (not (env | grep ^USER)) (puts "Nothing to see here...\n")
  puts "\n"
}

reporter "initial state"

{
  USERNAME :* "Bob"

  reporter "with a new environment variable"
}

reporter "back to initial state"

{
  USER :* "Sue"

  reporter "with a shadowed environment variable"
}

reporter "back to initial state"

{
  !* USER

  reporter "with an environment variable unset"
}

reporter "back to initial state"

USER = "Rita"

reporter "just a regular variable"

$ idio extend-env
initial state
USER=idf

with a new environment variable
USERNAME=Bob
USER=idf

back to initial state
USER=idf

with a shadowed environment variable
USER=Sue

back to initial state
USER=idf

with an environment variable removed
Nothing to see here...

back to initial state
USER=idf

just a regular variable
USER=Rita

Last built at 2024-05-21T06:11:39Z+0000 from 77077af (dev) for Idio 0.3