scripts: environment: Use system* instead of system.

This allows for direct program invokation without needing a shell to act
as a command interpreter.

* guix/scripts/environment.scm (%default-shell): New variable.
  (show-help): Adjust description.  Remove '--exec' reference.
  (%default-options): Use '%default-shell'.
  (%options): Adjust '--exec' to run command via the default shell.
  (parse-args): New procedure.
  (guix-environment): Use 'parse-args'.  Use 'system*' instead of
  'system'.
* tests/guix-environment.sh: Add test for '--' command invokation.
* doc/guix.texi ("Invoking guix environment"): Use new syntax.  Remove
  '--exec' documentation.

1 files changed, 6 insertions, 10 deletions

diff --git a/doc/guix.texi b/doc/guix.texi
index 6da7281566..39b76c7bf6 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -4538,11 +4538,12 @@ and Emacs are available:
 guix environment guile emacs
 @end example
 
-Sometimes an interactive shell session is not desired.  The
-@code{--exec} option can be used to specify the command to run instead.
+Sometimes an interactive shell session is not desired.  An arbitrary
+command may be invoked by placing the @code{--} token to separate the
+command from the rest of the arguments:
 
 @example
-guix environment guile --exec=make
+guix environment guile -- make -j4
 @end example
 
 In other situations, it is more convenient to specify the list of
@@ -4551,7 +4552,7 @@ runs @command{python} from an environment containing Python@tie{}2.7 and
 NumPy:
 
 @example
-guix environment --ad-hoc python2-numpy python-2.7 -E python
+guix environment --ad-hoc python2-numpy python-2.7 -- python
 @end example
 
 The available options are summarized below.
@@ -4582,11 +4583,6 @@ As an example, @var{file} might contain a definition like this
 @verbatiminclude environment-gdb.scm
 @end example
 
-
-@item --exec=@var{command}
-@item -E @var{command}
-Execute @var{command} in the new environment.
-
 @item --ad-hoc
 Include all specified packages in the resulting environment, as if an
 @i{ad hoc} package were defined with them as inputs.  This option is
@@ -4596,7 +4592,7 @@ package expression to contain the desired inputs.
 For instance, the command:
 
 @example
-guix environment --ad-hoc guile guile-sdl -E guile
+guix environment --ad-hoc guile guile-sdl -- guile
 @end example
 
 runs @command{guile} in an environment where Guile and Guile-SDL are