execline: the importas program
Keywords: execline command importas import environment variable

execline
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# The `importas` program

`importas` replaces a literal with the value of an environment variable, then executes another program.

## Interface

         importas [ -i | -D default ] [ -u ] [ -s ] [ -C | -c ] [ -N | -n ] [ -d delim ] variable envvar prog...
         importas -S [ -i | -D default ] [ -u ] [ -s ] [ -C | -c ] [ -N | -n ] [ -d delim ] envvar prog...

- `importas` fetches the value of envvar in the environment. If neither the -D nor the -i option is given, and envvar is undefined, no word is returned (that is different from the empty word).
- `importas` then performs variable substitution on prog..., with variable as key and that string as value.
- `importas` then execs into the modified prog....

## Options

- `-D` default : If this option is given and envvar is undefined, substitute default for the value of variable instead of no word. For instance, to substitute the empty word, use `-D ""`.
- `-i` : Insist. If envvar is undefined, `importas` will not do anything; instead, it will exit 100 with an error message. This has precedence over any `-D` option.
- `-u` : Unexport. envvar will be removed from the environment after the substitution. `importas -u variable envvar` is equivalent to `importas variable envvar unexport envvar`.
- `-S` : import with same name. This option allows variable to be omitted; it will be the same as envvar. In other words, `importas -S var` is the same as `importas var var`.
- Other options are used to control the substitution mechanism.

## Notes

- When envvar is undefined, and the `-D` option is not given, any variable substitution with variable as the key will return no word; that is true even when the `${variable}` form to be substituted happens in the middle of a word (with a prefix and/or a postfix), which means the whole word will be deleted. If this is not the behaviour you want, use the `-D` option.