From c4f0b6ccea128d52a7b4a9ddc1e81dcf13bb25ea Mon Sep 17 00:00:00 2001 From: Jim Porter Date: Sun, 15 Jan 2023 18:35:31 -0800 Subject: [PATCH] Add more detail about how to invoke Eshell commands * doc/misc/eshell.texi (Variables): Move footnote explaining "REPL" from here... (Top): ... to its first use here. (Commands): Move explanation about kernel functions to here. (Invocation): Describe command form and Lisp form. Fix documentation about priority of commands in command form. (Arguments): Add a cross reference to the Invocation node. --- doc/misc/eshell.texi | 136 +++++++++++++++++++++++++++++++------------ 1 file changed, 100 insertions(+), 36 deletions(-) diff --git a/doc/misc/eshell.texi b/doc/misc/eshell.texi index 4ad1c3f74f6..1789cded9d3 100644 --- a/doc/misc/eshell.texi +++ b/doc/misc/eshell.texi @@ -64,10 +64,11 @@ modify this GNU manual.'' Eshell is a shell-like command interpreter implemented in Emacs Lisp. It invokes no external processes except for those requested by the -user. It is intended to be an alternative to the IELM (@pxref{Lisp Interaction, Emacs Lisp Interaction, , emacs, The Emacs Editor}) -REPL for Emacs @emph{and} with an interface similar to command shells -such as @command{bash}, @command{zsh}, @command{rc}, or -@command{4dos}. +user. It is intended to be an alternative to the IELM (@pxref{Lisp +Interaction, Emacs Lisp Interaction, , emacs, The Emacs Editor}) +REPL@footnote{Short for ``Read-Eval-Print Loop''.} for Emacs +@emph{and} with an interface similar to command shells such as +@command{bash}, @command{zsh}, @command{rc}, or @command{4dos}. @c This manual is updated to release 2.4 of Eshell. @insertcopying @@ -193,6 +194,13 @@ In a command shell, everything is done by invoking commands. This 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 this as the Eshell prompt: +@kbd{eshell-parse-command 'echo hello'}} + @menu * Invocation:: * Arguments:: @@ -207,23 +215,16 @@ history and invoking commands in a script file. @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 +233,80 @@ the foreground. That said, background processes invoked from Eshell 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 + +@cindex order of looking for commands +@cindex command lookup order +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}. This will swap the lookup order of the last two items. + +You can also group command forms together into a subcommand with curly +braces (@code{@{@}}). This lets you use the output of a subcommand as +an argument to another command, or within control flow statements +(@pxref{Control Flow}). + +@example +~ $ echo @{echo hello; echo there@} +hellothere +@end example + +@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 + +This command writes a list of all files matching the glob pattern +@code{*.patch} (@pxref{Globbing}) to a file named +@code{@var{current-date}.log} (@pxref{Redirection}). + @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 Lisp form +(@pxref{Invocation}): @example ~ $ echo (list 1 2 3) @@ -354,10 +423,6 @@ eshell/sudo is a compiled Lisp function in `em-tramp.el'. 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. @@ -923,15 +988,14 @@ For example, you could handle a subset of the options for the @node Variables @section Variables @vindex eshell-prefer-lisp-variables -Since Eshell is a combination of an Emacs @acronym{REPL}@footnote{ -Short for ``Read-Eval-Print Loop''. -} and a command shell, it can refer to variables from two different -sources: ordinary Emacs Lisp variables, as well as environment -variables. By default, when using a variable in Eshell, it will first -look in the list of built-in variables, then in the list of -environment variables, and finally in the list of Lisp variables. If -you would prefer to use Lisp variables over environment variables, you -can set @code{eshell-prefer-lisp-variables} to @code{t}. +Since Eshell is a combination of an Emacs @acronym{REPL} and a command +shell, it can refer to variables from two different sources: ordinary +Emacs Lisp variables, as well as environment variables. By default, +when using a variable in Eshell, it will first look in the list of +built-in variables, then in the list of environment variables, and +finally in the list of Lisp variables. If you would prefer to use +Lisp variables over environment variables, you can set +@code{eshell-prefer-lisp-variables} to @code{t}. You can set variables in a few different ways. To set a Lisp variable, you can use the command @samp{setq @var{name} @var{value}}, -- 2.39.2