FBB::ReadLineStream - std::istream offering line-editing and
history
#include <bobcat/readlinestream>
Linking option: -lreadline -lbobcat
A FBB::ReadLineStream object is a std::istream
objects, allowing line-editing and history manipulation.
The ReadLineStream class uses Gnu’s readline library
to allow editing of input lines. The ReadLineStream object can be
used to construct a std::istream allowing in-line editing of lines
read from the terminal. All lines may be preceded by a configurable
prompt.
Since Gnu’s readline library operates on global data there
can only be one ReadLineStream (and underlying ReadLineBuf)
object. ReadLineStream is a singleton class: in any program there can
only be one ReadLineStream object.
ReadLineStream offers editing capabilities while the user
is entering lines. Like Gnu’s readline(3) function, the line
editing commands are by default similar to those of emacs(1), but can
easily be reconfigured, e.g. to offer vi(1)-like characteristics.
History manipulation is provided as an option. The collected
history may be accessed for reading using an FBB::ReadLineHistory
object.
Specific information about the facilities offered by the Gnu
software used by ReadLineStream is provided in the GNU Readline
Library documentation
(http://cnswww.cns.cwru.edu/php/chet/readline/rltop.html).
Gnu’s readline function reads its information from
the standard input file. Programs using ReadLineStream should
normally not extract information from std::cin. However, as the
standard input file has a file descriptor (0), redirection should be
possible (e.g., using FBB::Redirector).
When the command line is kept, history expansion is offered as an
option. History expansion introduces words from the history list into the
input stream, making it easy to repeat commands, to insert elements of a
previous input line into the current input line, or to fix errors in
previous command lines.
History expansion is usually performed immediately after a
complete line is read.
The line selected from the history is called the event, and
the portions of that line that are processed are called words.
Various modifiers are available to manipulate selected words. This is
comparable to the way a program like bash(1) breaks up its input line
into `words’.
History expansion is introduced by the use of the history
expansion character, by default equal to the !-character. Only
backslash (\) and single quotes can change the history expansion
character into a normal character.
The remainder of this section is copied almost verbatim from the
history(3) man-page. The reader is referred to that man-page or to
the Gnu History Library documentation for further details.
The following event designators are supported:
- o
- !: starts a history substitution, except when followed by a blank,
newline, = or (.
- o
- !n: refers to command line n.
- o
- !-n: refers to the current command line minus n.
- o
- !! refers to the previous command. This is a synonym for
`!-1’.
- o
- !string refers to the most recent command starting with
string.
- o
- !?string[?] refers to the most recent command containing string.
The trailing ? may be omitted if string is followed immediately by
a newline.
- o
- ^string1^string2^ (quick substitution) repeats the last command,
replacing string1 with string2. Equivalent to
!!:s/string1/string2/.
- o
- !# the entire command line typed so far.
Word Designators
Word designators are used to select desired words from the event.
A : separates the event specification from the word designator. It
may be omitted if the word designator begins with a ^, $, *, -, or
%. Words are numbered from the beginning of the line, with the first
word being denoted by 0 (zero). Words are inserted into the current line
separated by single spaces.
- o
- 0 (zero) The zeroth word. For the shell, this is the command
word.
- o
- n The nth word.
- o
- ^ The first argument. That is, word 1.
- o
- $ The last argument.
- o
- % The word matched by the most recent ?string? search.
- o
- x-y A range of words; `-y’ abbreviates `0-y’.
- o
- * All of the words but the zeroth. This is a synonym for
1-$. It is not an error to use * if there is just one word in the
event; the empty string is returned in that case.
- o
- x* Abbreviates x-$.
- o
- x- Abbreviates x-$ like x*, but omits the last word.
If a word designator is supplied without an event specification, the
previous command is used as the event.
Modifiers
After the optional word designator, there may appear a sequence of
one or more of the following modifiers, each preceded by a :.
- o
- h removes a trailing file name component, leaving only the
head.
- o
- t removes all leading file name components, leaving the tail.
- o
- r removes a trailing suffix of the form .xxx, leaving the
basename.
- o
- e removes all but the trailing suffix.
- o
- p prints the new command but does not execute it.
- o
- q quotes the substituted words, escaping further
substitutions.
- o
- x quotes the substituted words as with q, but break into words at
blanks and newlines.
- o
- s/old/new/ substitutes new for the first occurrence of old in the
event line. Any delimiter can be used in place of /. The final
delimiter is optional if it is the last character of the event line. The
delimiter may be quoted in old and new with a single backslash. If
& appears in new, it is replaced by old. A single backslash
will quote the &. If old is null, it is set to the last
old substituted, or, if no previous history substitutions took place, the
last string in a !?string[?] search.
- o
- & repeats the previous substitution.
- o
- g Causes changes to be applied over the entire event line. This is
used in conjunction with :s (e.g., :gs/old/new/) or
:&. If used with :s, any delimiter can be used in place
of /, and the final delimiter is optional if it is the last
character of the event line. An a may be used as a synonym for
g.
- o
- G Apply the following s modifier once to each word in the
event line.
FBB
All constructors, members, operators and manipulators, mentioned in this
man-page, are defined in the namespace FBB.
FBB::ReadLineBuf (privately), std::istream
(publicly)
The enum Type defines the following value:
- o
- DONT_EXPAND_HISTORY: history expansion is not requested;
- o
- EXPAND_HISTORY: history expansion is requested.
The enum Expansion provides meaningful return values for
the history expansion process. Its values are:
- o
- DONT_EXEC: history expansion succeeded, but the expanded line
should not be executed. E.g., after entering the line
ls *
the line
!!:p
should cause the using program to display, rather than exectute
ls *. Note that interpretation of this expansion return
value is not the task of the ReadLineBuf object, but of the program
using the ReadLineBuf object.
- o
- ERROR: the history expansion failed. See also the member
expansionError below;
- o
- EXPANDED: the history expansion succeeded;
- o
- NO_EXPANSION: no history expansion took place.
Preamble: since there can only be one ReadLineBuf object,
any attempt to define a second ReadLineStream object will fail as
there can only be a single ReadLineBuf object in any program. An
attempt to define a second ReadLineBuf object results in a
logic_error exception being thrown.
- o
- ReadLineStream(std::string const &prompt = "", Type type
= NO_EXPANSION):
This constructor initializes the ReadLineStream object with an
initial prompt, using a history of at most
std::numeric_limits<int>::max() lines, by default not using
history expansion.
- o
- ReadLineStream(std::string const &prompt, size_t historySize,
Type type = NO_EXPANSION):
This constructor initializes the ReadLineStream with an initial
prompt, an initial history of a predefined maximum size, by default not
using history expansion. Specifying a history size 0 results in no history
being kept, any value equal to or exceeding the predefined constant
std::numeric_limits<int>::max() results in a history of at
most std::numeric_limits<int>::max() lines. If no history is
requested but type is specified as EXPAND_HISTORY a
logic_error exception is thrown.
Copy and move constructors (and assignment operators) are not
available.
All members of std::streambuf are available, as
FBB::ReadLineStream inherits from this class.
- o
- ReadLineStream::Expansion expansion() const:
The status of the history expansion after retrieving a line from the
terminal is returned. Its value is determined after each line retrieved
from the terminal. If no history expansion is requested it returns
Expansion::ERROR.
- o
- std::string const &expansionError() const:
A short textual description of the nature of the error when expansion
returns Expansion::ERROR is returned. If no history expansion is
requested an empty string is returned.
- o
- bool setExpansion(Type type):
History expansion can be activated or stopped using this member. When
history expansion is requested but the ReadLineStream object
maintains no history the function returns false. Otherwise it
returns true.
- o
- void setPrompt(std::string const &prompt = ""):
The prompt that is displayed in front of the next line read from the
terminal can be modified by this member. When called without arguments no
prompt will be displayed. setPrompt can be called while input lines
are being received. The new prompt will be active after the current line
has been read from the terminal.
- o
- bool useTimestamps(std::string (*timestamp)() = 0):
When initialized with the address of a function returning a
std::string the entered commands will be given a timestamp equal to
the text returned by the function pointed to by timestamp. The
timestamps can be retrieved using the ReadLineHistory(3) object. By
default or after passing an explicit 0-pointer to useTimestamps no
timestamps are stored. The value false is returned when no history
is kept, otherwise true is returned.
#include <iostream>
#include <istream>
#include <cstdio>
#include <sstream>
#include <iomanip>
#include <bobcat/readlinestream>
using namespace std;
using namespace FBB;
int main()
{
ReadLineStream in("", 10, ReadLineBuf::EXPAND_HISTORY);
size_t count = 0;
string line;
while (true)
{
ostringstream prompt;
prompt << setw(2) << ++count << ": ";
in.setPrompt(prompt.str());
if (!getline(in, line)) // uses the last-set prompt
break;
cout << "Retrieved: " << line << "\n"
"Expansion status: ";
switch (in.expansion())
{
case ReadLineBuf::ERROR:
cout << "ERROR: " << in.expansionError() << ’\n’;
break;
case ReadLineBuf::NO_EXPANSION:
cout << "no expansion performed\n";
break;
case ReadLineBuf::DONT_EXEC:
cout << "don’t execute the expanded line\n";
break;
case ReadLineBuf::EXPANDED:
cout << "expansion successfully performed\n";
break;
}
}
}
bobcat/readlinebuf - defines the class interface
- o
- https://fbb-git.gitlab.io/bobcat/: gitlab project page;
- o
- bobcat_5.07.00-x.dsc: detached signature;
- o
- bobcat_5.07.00-x.tar.gz: source archive;
- o
- bobcat_5.07.00-x_i386.changes: change log;
- o
- libbobcat1_5.07.00-x_*.deb: debian package containing the
libraries;
- o
- libbobcat1-dev_5.07.00-x_*.deb: debian package containing the
libraries, headers and manual pages;
Bobcat is an acronym of `Brokken’s Own Base Classes And
Templates’.
This is free software, distributed under the terms of the GNU
General Public License (GPL).
Frank B. Brokken (f.b.brokken@rug.nl).