29.2. Readline Interaction
Often during an interactive session you type in a long line of text,
only to notice that the first word on the line is misspelled. The
Readline library gives you a set of commands for manipulating the text
as you type it in, allowing you to just fix your typo, and not forcing
you to retype the majority of the line. Using these editing commands,
you move the cursor to the place that needs correction, and delete or
insert the text of the corrections. Then, when you are satisfied with
the line, you simply press [RET]. You do not have to be at the
end of the line to press [RET]; the entire line is accepted
regardless of the location of the cursor within the line.
29.2.1. Readline Bare Essentials
In order to enter characters into the line, simply type them. The typed
character appears where the cursor was, and then the cursor moves one
space to the right. If you mistype a character, you can use your
erase character to back up and delete the mistyped character.
Sometimes you may mistype a character, and
not notice the error until you have typed several other characters. In
that case, you can type C-b to move the cursor to the left, and then
correct your mistake. Afterwards, you can move the cursor to the right
with C-f.
When you add text in the middle of a line, you will notice that characters
to the right of the cursor are `pushed over' to make room for the text
that you have inserted. Likewise, when you delete text behind the cursor,
characters to the right of the cursor are `pulled back' to fill in the
blank space created by the removal of the text. A list of the bare
essentials for editing the text of an input line follows.
- C-b
Move back one character.
- C-f
Move forward one character.
- [DEL] or [Backspace]
Delete the character to the left of the cursor.
- C-d
Delete the character underneath the cursor.
- Printing characters
Insert the character into the line at the cursor.
- C-_ or C-x C-u
Undo the last editing command. You can undo all the way back to an
empty line.
(Depending on your configuration, the [Backspace] key be set to
delete the character to the left of the cursor and the [DEL] key set
to delete the character underneath the cursor, like C-d, rather
than the character to the left of the cursor.)
29.2.2. Readline Movement Commands
The above table describes the most basic keystrokes that you need
in order to do editing of the input line. For your convenience, many
other commands have been added in addition to C-b, C-f,
C-d, and [DEL]. Here are some commands for moving more rapidly
about the line.
- C-a
Move to the start of the line.
- C-e
Move to the end of the line.
- M-f
Move forward a word, where a word is composed of letters and digits.
- M-b
Move backward a word.
- C-l
Clear the screen, reprinting the current line at the top.
Notice how C-f moves forward a character, while M-f moves
forward a word. It is a loose convention that control keystrokes
operate on characters while meta keystrokes operate on words.
29.2.3. Readline Killing Commands
Killing text means to delete the text from the line, but to save
it away for later use, usually by yanking (re-inserting)
it back into the line.
(`Cut' and `paste' are more recent jargon for `kill' and `yank'.)
If the description for a command says that it `kills' text, then you can
be sure that you can get the text back in a different (or the same)
place later.
When you use a kill command, the text is saved in a kill-ring.
Any number of consecutive kills save all of the killed text together, so
that when you yank it back, you get it all. The kill
ring is not line specific; the text that you killed on a previously
typed line is available to be yanked back later, when you are typing
another line.
Here is the list of commands for killing text.
- C-k
Kill the text from the current cursor position to the end of the line.
- M-d
Kill from the cursor to the end of the current word, or, if between
words, to the end of the next word.
Word boundaries are the same as those used by M-f.
- M-[DEL]
Kill from the cursor the start of the current word, or, if between
words, to the start of the previous word.
Word boundaries are the same as those used by M-b.
- C-w
Kill from the cursor to the previous whitespace. This is different than
M-[DEL] because the word boundaries differ.
Here is how to yank the text back into the line. Yanking
means to copy the most-recently-killed text from the kill buffer.
- C-y
Yank the most recently killed text back into the buffer at the cursor.
- M-y
Rotate the kill-ring, and yank the new top. You can only do this if
the prior command is C-y or M-y.
29.2.4. Readline Arguments
You can pass numeric arguments to Readline commands. Sometimes the
argument acts as a repeat count, other times it is the sign of the
argument that is significant. If you pass a negative argument to a
command which normally acts in a forward direction, that command will
act in a backward direction. For example, to kill text back to the
start of the line, you might type M- C-k.
The general way to pass numeric arguments to a command is to type meta
digits before the command. If the first `digit' typed is a minus
sign (-), then the sign of the argument will be negative. Once
you have typed one meta digit to get the argument started, you can type
the remainder of the digits, and then the command. For example, to give
the C-d command an argument of 10, you could type M-1 0 C-d,
which will delete the next ten characters on the input line.
29.2.5. Searching for Commands in the History
Readline provides commands for searching through the command history
for lines containing a specified string.
There are two search modes: incremental and non-incremental.
Incremental searches begin before the user has finished typing the
search string.
As each character of the search string is typed, Readline displays
the next entry from the history matching the string typed so far.
An incremental search requires only as many characters as needed to
find the desired history entry.
To search backward in the history for a particular string, type
C-r. Typing C-s searches forward through the history.
The characters present in the value of the isearch-terminators variable
are used to terminate an incremental search.
If that variable has not been assigned a value, the [ESC] and
C-J characters will terminate an incremental search.
C-g will abort an incremental search and restore the original line.
When the search is terminated, the history entry containing the
search string becomes the current line.
To find other matching entries in the history list, type C-r or
C-s as appropriate.
This will search backward or forward in the history for the next
entry matching the search string typed so far.
Any other key sequence bound to a Readline command will terminate
the search and execute that command.
For instance, a [RET] will terminate the search and accept
the line, thereby executing the command from the history list.
A movement command will terminate the search, make the last line found
the current line, and begin editing.
Readline remembers the last incremental search string. If two
C-rs are typed without any intervening characters defining a new
search string, any remembered search string is used.
Non-incremental searches read the entire search string before starting
to search for matching history lines. The search string may be
typed by the user or be part of the contents of the current line.
