@node Dollars Expansion
@section Dollars Expansion
-Eshell has different @code{$} expansion syntax from other shells. There
-are some similarities, but don't let these lull you into a false sense
-of familiarity.
+Like in many other shells, you can use @code{$} expansions to insert
+various values into your Eshell invocations. While Eshell's @code{$}
+expansion syntax has some similarities to the syntax from other
+shells, there are also many differences. Don't let these similarities
+lull you into a false sense of familiarity.
+
+When using command form (@pxref{Invocation}), Eshell will ignore any
+leading nil values, so if @var{foo} is @code{nil}, @samp{$@var{foo}
+echo hello} is equivalent to @samp{echo hello}.
@table @code
COMMAND may result in an alias being executed, or a plain command."
(unless eshell-allow-commands
(signal 'eshell-commands-forbidden '(named)))
+ ;; Strip off any leading nil values. This can only happen if a
+ ;; variable evaluates to nil, such as "$var x", where `var' is nil.
+ ;; In that case, the command name becomes `x', for compatibility
+ ;; with most regular shells (the difference is that they do an
+ ;; interpolation pass before the argument parsing pass, but Eshell
+ ;; does both at the same time).
+ (while (and (not command) args)
+ (setq command (pop args)))
(setq eshell-last-arguments args
- eshell-last-command-name (eshell-stringify command))
+ eshell-last-command-name (eshell-stringify command))
(run-hook-with-args 'eshell-prepare-command-hook)
(cl-assert (stringp eshell-last-command-name))
- (if eshell-last-command-name
- (or (run-hook-with-args-until-success
- 'eshell-named-command-hook eshell-last-command-name
- eshell-last-arguments)
- (eshell-plain-command eshell-last-command-name
- eshell-last-arguments))))
+ (when eshell-last-command-name
+ (or (run-hook-with-args-until-success
+ 'eshell-named-command-hook eshell-last-command-name
+ eshell-last-arguments)
+ (eshell-plain-command eshell-last-command-name
+ eshell-last-arguments))))
(defalias 'eshell-named-command* 'eshell-named-command)
(defun eshell-handle-local-variables ()
"Allow for the syntax `VAR=val <command> <args>'."
- ;; strip off any null commands, which can only happen if a variable
- ;; evaluates to nil, such as "$var x", where `var' is nil. The
- ;; command name in that case becomes `x', for compatibility with
- ;; most regular shells (the difference is that they do an
- ;; interpolation pass before the argument parsing pass, but Eshell
- ;; does both at the same time).
- (while (and (not eshell-last-command-name)
- eshell-last-arguments)
- (setq eshell-last-command-name (car eshell-last-arguments)
- eshell-last-arguments (cdr eshell-last-arguments)))
+ ;; Eshell handles local variable settings (e.g. 'CFLAGS=-O2 make')
+ ;; by making the whole command into a subcommand, and calling
+ ;; `eshell-set-variable' immediately before the command is invoked.
+ ;; This means that 'FOO=x cd bar' won't work exactly as expected,
+ ;; but that is by no means a typical use of local environment
+ ;; variables.
(let ((setvar "\\`\\([A-Za-z_][A-Za-z0-9_]*\\)=\\(.*\\)\\'")
- (command (eshell-stringify eshell-last-command-name))
- (args eshell-last-arguments))
- ;; local variable settings (such as 'CFLAGS=-O2 make') are handled
- ;; by making the whole command into a subcommand, and calling
- ;; setenv immediately before the command is invoked. This means
- ;; that 'BLAH=x cd blah' won't work exactly as expected, but that
- ;; is by no means a typical use of local environment variables.
- (if (and command (string-match setvar command))
- (throw
- 'eshell-replace-command
- (list
- 'eshell-as-subcommand
- (append
- (list 'progn)
- (let ((l (list t)))
- (while (string-match setvar command)
- (nconc
- l (list
- (list 'eshell-set-variable
- (match-string 1 command)
- (match-string 2 command))))
- (setq command (eshell-stringify (car args))
- args (cdr args)))
- (cdr l))
- (list (list 'eshell-named-command
- command (list 'quote args)))))))))
+ (command eshell-last-command-name)
+ (args eshell-last-arguments))
+ (when (and (stringp command) (string-match setvar command))
+ (throw 'eshell-replace-command
+ `(eshell-as-subcommand
+ (progn
+ ,@(let (locals)
+ (while (and (stringp command)
+ (string-match setvar command))
+ (push `(eshell-set-variable
+ ,(match-string 1 command)
+ ,(match-string 2 command))
+ locals)
+ (setq command (pop args)))
+ (nreverse locals))
+ (eshell-named-command ,command ,(list 'quote args)))
+ )))))
(defun eshell-interpolate-variable ()
"Parse a variable interpolation.
(eshell-match-command-output "echo ${echo $value}"
"hello\n")))
+(ert-deftest esh-cmd-test/skip-leading-nils ()
+ "Test that Eshell skips leading nil arguments for named commands."
+ (eshell-command-result-equal "$eshell-test-value echo hello" "hello")
+ (eshell-command-result-equal
+ "$eshell-test-value $eshell-test-value echo hello" "hello"))
+
(ert-deftest esh-cmd-test/let-rebinds-after-defer ()
"Test that let-bound values are properly updated after `eshell-defer'.
When inside a `let' block in an Eshell command form, we need to
(eshell-match-command-output "VAR=hello env" "VAR=hello\n")
(should (equal (getenv "VAR") "value"))))
+(ert-deftest esh-var-test/local-variables/skip-nil ()
+ "Test that Eshell skips leading nil arguments after local variable setting."
+ (with-temp-eshell
+ (push "VAR=value" process-environment)
+ (eshell-match-command-output "VAR=hello $eshell-test-value env"
+ "VAR=hello\n")
+ (should (equal (getenv "VAR") "value"))))
+
\f
;; Variable aliases
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