From d0e4b94623b5840a212c97c75b1641dbbbff77ea Mon Sep 17 00:00:00 2001
From: Jim Porter <jporterbugs@gmail.com>
Date: Sun, 15 Jan 2023 18:35:31 -0800
Subject: [PATCH] Add more detail about how to invoke Eshell commands

* doc/misc/eshell.texi (Commands): Move explanation about kernel
functions to here.
(Invocation): Describe command form and Lisp form.  Fix documentation
about priority of commands in command form.
---
 doc/misc/eshell.texi | 93 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 70 insertions(+), 23 deletions(-)

diff --git a/doc/misc/eshell.texi b/doc/misc/eshell.texi
index fc7d52eb711..b5444741b66 100644
--- a/doc/misc/eshell.texi
+++ b/doc/misc/eshell.texi
@@ -193,6 +193,12 @@ Commands
 chapter covers command invocations in Eshell, including the command
 history and invoking commands in a script file.
 
+Unlike regular system shells, Eshell never invokes kernel functions
+directly, such as @code{exec(3)}.  Instead, it uses the Lisp functions
+available in the Emacs Lisp library.  It does this by transforming the
+input line into a callable Lisp form.@footnote{To see the Lisp form
+that will be invoked, type: @samp{eshell-parse-command 'echo hello'}}
+
 @menu
 * Invocation::
 * Arguments::
@@ -207,23 +213,16 @@ Commands
 
 @node Invocation
 @section Invocation
-Unlike regular system shells, Eshell never invokes kernel functions
-directly, such as @code{exec(3)}.  Instead, it uses the Lisp functions
-available in the Emacs Lisp library.  It does this by transforming the
-input line into a callable Lisp form.@footnote{To see the Lisp form that will be invoked, type: @samp{eshell-parse-command "echo hello"}}
+Eshell is both a command shell and an Emacs Lisp @acronym{REPL}.  As a
+result, you can invoke commands in two different ways: in @dfn{command
+form} or in @dfn{lisp form}.
 
-The command can be either an Elisp function or an external command.
-Eshell looks first for an alias (@pxref{Aliases}) with the same name as the
-command, then a built-in (@pxref{Built-ins}) or a function with the
-same name; if there is no match, it then tries to execute it as an
-external command.
-
-The semicolon (@code{;}) can be used to separate multiple command
-invocations on a single line.  You can also separate commands with
-@code{&&} or @code{||}. When using @code{&&}, Eshell will execute the
-second command only if the first succeeds (i.e.@: has an exit
-status of 0); with @code{||}, Eshell will execute the second command
-only if the first fails.
+You can use the semicolon (@code{;}) to separate multiple command
+invocations on a single line, executing each in turn.  You can also
+separate commands with @code{&&} or @code{||}. When using @code{&&},
+Eshell will execute the second command only if the first succeeds
+(i.e.@: has an exit status of 0); with @code{||}, Eshell will execute
+the second command only if the first fails.
 
 A command invocation followed by an ampersand (@code{&}) will be run
 in the background.  Eshell has no job control, so you can not suspend
@@ -232,12 +231,64 @@ Invocation
 can be controlled the same way as any other background process in
 Emacs.
 
+@subsection Command form
+Command form looks much the same as in other shells.  A command
+consists of arguments separated by spaces; the first argument is the
+command to run, with any subsequent arguments being passed to that
+command.
+
+@example
+~ $ echo hello
+hello
+@end example
+
+The command can be either an Elisp function or an external command.
+Eshell looks for the command in the following order:
+
+@enumerate
+@item
+As a command alias (@pxref{Aliases})
+
+@item
+As a built-in command (@pxref{Built-ins})
+
+@item
+As an external program
+
+@item
+As an ordinary Lisp function
+@end enumerate
+
+@vindex eshell-prefer-lisp-functions
+If you would prefer to use ordinary Lisp functions over external
+programs, set the option @code{eshell-prefer-lisp-functions} to
+@code{t}.
+
+@subsection Lisp form
+Lisp form looks like ordinary Emacs Lisp code, because that's what it
+is.  As a result, you can use any syntax normally available to an
+Emacs Lisp program (@pxref{Top, , , elisp, The Emacs Lisp Reference
+Manual}).
+
+@example
+~ $ (format "hello, %s" user-login-name)
+hello, user
+@end example
+
+In addition, you can @emph{combine} command forms and Lisp forms
+together into single statements, letting you use whatever form is the
+most convenient for expressing your intentions.
+
+@example
+~ $ ls *.patch > (format-time-string "%F.log")
+@end example
+
 @node Arguments
 @section Arguments
-Ordinarily, command arguments are parsed by Eshell as either strings
+Ordinarily, Eshell parses arguments in command form as either strings
 or numbers, depending on what the parser thinks they look like.  To
-specify an argument of some other data type, you can use an
-@ref{Dollars Expansion, Elisp expression}:
+specify an argument of some other data type, you can use a
+@ref{Invocation, Lisp form}:
 
 @example
 ~ $ echo (list 1 2 3)
@@ -354,10 +405,6 @@ Built-ins
 sudo is an alias, defined as "*sudo $@@*"
 @end example
 
-@vindex eshell-prefer-lisp-functions
-If you would prefer to use the built-in commands instead of the external
-commands, set @code{eshell-prefer-lisp-functions} to @code{t}.
-
 Some of the built-in commands have different behavior from their
 external counterparts, and some have no external counterpart.  Most of
 these will print a usage message when given the @code{--help} option.
-- 
2.25.1