Next: , Up: Expansion

3.1 Dollars Expansion

Eshell has different $ expansion syntax from other shells. There are some similarities, but don't let these lull you into a false sense of familiarity.

Expands to the value bound to var. This is the main way to use variables in command invocations.
Expands to the length of the value bound to var. Raises an error if the value is not a sequence (see Sequences).
Expands to the result of evaluating the S-expression (lisp). On its own, this is identical to just (lisp), but with the $, it can be used in a string, such as ‘/some/path/$(lisp).txt’.
Returns the output of command, which can be any valid Eshell command invocation, and may even contain expansions.
Expands to the ith element of the value bound to var. If the value is a string, it will be split at whitespace to make it a list. Again, raises an error if the value is not a sequence.
$var[: i]
As above, but now splitting occurs at the colon character.
$var[: i j]
As above, but instead of returning just a string, it now returns a list of two strings. If the result is being interpolated into a larger string, this list will be flattened into one big string, with each element separated by a space.
$var["\\\\" i]
Separate on backslash characters. Actually, the first argument – if it doesn't have the form of a number, or a plain variable name – can be any regular expression. So to split on numbers, use ‘$var["[0-9]+" 10 20]’.
Calls assoc on var with "hello", expecting it to be an alist (see Association Lists).
Returns the length of the cdr of the element of var who car is equal to "hello".