(R-intro.info)The command-line editor

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Appendix C The command-line editor
**********************************

C.1 Preliminaries
=================

When the GNU *readline* library is available at the time R is configured
for compilation under UNIX, an inbuilt command line editor allowing
recall, editing and re-submission of prior commands is used.  Note that
other versions of *readline* exist and may be used by the inbuilt
command line editor: this used to happen on macOS.

   It can be disabled (useful for usage with ESS (1)) using the startup
option '--no-readline'.

   Windows versions of R have somewhat simpler command-line editing: see
'Console' under the 'Help' menu of the GUI, and the file 'README.Rterm'
for command-line editing under 'Rterm.exe'.

   When using R with GNU(2) *readline* capabilities, the functions
described below are available, as well as others (probably) documented
in 'man readline' or 'info readline' on your system.

   Many of these use either Control or Meta characters.  Control
characters, such as 'Control-m', are obtained by holding the <CTRL> down
while you press the <m> key, and are written as 'C-m' below.  Meta
characters, such as 'Meta-b', are typed by holding down <META>(3) and
pressing <b>, and written as 'M-b' in the following.  If your terminal
does not have a <META> key enabled, you can still type Meta characters
using two-character sequences starting with 'ESC'.  Thus, to enter
'M-b', you could type <ESC><b>.  The 'ESC' character sequences are also
allowed on terminals with real Meta keys.  Note that case is significant
for Meta characters.

   Some but not all versions(4) of *readline* will recognize resizing of
the terminal window so this is best avoided.

C.2 Editing actions
===================

The R program keeps a history of the command lines you type, including
the erroneous lines, and commands in your history may be recalled,
changed if necessary, and re-submitted as new commands.  In Emacs-style
command-line editing any straight typing you do while in this editing
phase causes the characters to be inserted in the command you are
editing, displacing any characters to the right of the cursor.  In _vi_
mode character insertion mode is started by 'M-i' or 'M-a', characters
are typed and insertion mode is finished by typing a further <ESC>.
(The default is Emacs-style, and only that is described here: for _vi_
mode see the *readline* documentation.)

   Pressing the <RET> command at any time causes the command to be
re-submitted.

   Other editing actions are summarized in the following table.

C.3 Command-line editor summary
===============================

Command recall and vertical motion
----------------------------------

'C-p'
     Go to the previous command (backwards in the history).
'C-n'
     Go to the next command (forwards in the history).
'C-r TEXT'
     Find the last command with the TEXT string in it.  This can be
     cancelled by 'C-g' (and on some versions of R by 'C-c').

   On most terminals, you can also use the up and down arrow keys
instead of 'C-p' and 'C-n', respectively.

Horizontal motion of the cursor
-------------------------------

'C-a'
     Go to the beginning of the command.
'C-e'
     Go to the end of the line.
'M-b'
     Go back one word.
'M-f'
     Go forward one word.
'C-b'
     Go back one character.
'C-f'
     Go forward one character.

   On most terminals, you can also use the left and right arrow keys
instead of 'C-b' and 'C-f', respectively.

Editing and re-submission
-------------------------

'TEXT'
     Insert TEXT at the cursor.
'C-f TEXT'
     Append TEXT after the cursor.
'<DEL>'
     Delete the previous character (left of the cursor).
'C-d'
     Delete the character under the cursor.
'M-d'
     Delete the rest of the word under the cursor, and "save" it.
'C-k'
     Delete from cursor to end of command, and "save" it.
'C-y'
     Insert (yank) the last "saved" text here.
'C-t'
     Transpose the character under the cursor with the next.
'M-l'
     Change the rest of the word to lower case.
'M-c'
     Change the rest of the word to upper case.
'<RET>'
     Re-submit the command to R.

   The final <RET> terminates the command line editing sequence.

   The *readline* key bindings can be customized in the usual way _via_
a '~/.inputrc' file.  These customizations can be conditioned on
application 'R', that is by including a section like

     $if R
       "\C-xd": "q('no')\n"
     $endif

   ---------- Footnotes ----------

   (1) The 'Emacs Speaks Statistics' package; see the URL
<https://ESS.R-project.org/>

   (2) It is possible to build R using an emulation of GNU *readline*,
such as one based on NetBSD's *editline*, it which case only a subset of
the capabilities may be provided.

   (3) On a PC keyboard this is usually the Alt key, occasionally the
'Windows' key.  On a Mac keyboard normally no meta key is available.

   (4) In particular, not versions 6.3 or later: this is worked around
as from R 3.4.0.