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troglobit / editline

A small replacement for GNU readline() for UNIX
https://troglobit.com/projects/editline/
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Editline

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Table of Contents

Introduction

This is a small line editing library. It can be linked into almost any program to provide command line editing and history functions. It is call compatible with the FSF readline library, but at a fraction of the size, and as a result fewer features. It is also distributed under a much more liberal License.

The small size (<30k), lack of dependencies (ncurses not needed!), and the free license should make this library interesting to many embedded developers.

Editline has several optional build-time features that can be enabled by supplying different options to the GNU configure script. See the output from configure --help for details. Some useful hints on how to use the library is available in the examples/ directory.

Editline is maintained collaboratively at GitHub.

Note: Windows is not a supported target for editline.

Example

Below is a very brief example to illustrate how one can use Editline to create a simple CLI, Ctrl-D exits the program. A slightly more advanced example is Jush, https://github.com/troglobit/jush/, a small and very simplistic UNIX shell. The Editline sources also include an examples/ sub-directory.

  1. Build and install the library, preferably using a release tarball The configure script defaults to a /usr/local prefix.

    tar xf editline-1.15.3.tar.xz
cd editline-1.15.3/
./configure --prefix=/usr
make all
sudo make install

  2. Place the below source code in a separate project directory, e.g. ~/src/example.c

    #include <stdio.h>
    #include <stdlib.h>
    #include <editline.h>

    int main(void)
    {
        char *p;

        while ((p = readline("CLI> ")) != NULL) {
            puts(p);
            free(p);
        }

        return 0;
    }

  1. Compile the example:

    cd ~/src/
make LDLIBS=-leditline example

Here I use make and rely on its implicit (built-in) rules to handle all the compiler magic, but you may want to create your own Makefile for the project. In particular if you don't change the default prefix (above), because then you need to specify the search path for the include file(s) and the library manually.

A simple ~/src/Makefile could look like this:

CFLAGS    = -I/usr/local/include
LDFLAGS   = -L/usr/local/lib
LDLIBS    = -leditline
EXEC      = example
OBJS      = example.o

all: $(EXEC)

$(EXEC): $(OBJS)

clean:
        $(RM) $(OBJS) $(EXEC)

distclean: clean
        $(RM) *.o *~ *.bak

Then simply type make from your ~/src/ directory. You can also use pkg-config for your ~/src/Makefile, replace the following lines:

CFLAGS    = $(shell pkg-config --cflags libeditline)
LDFLAGS   = $(shell pkg-config --libs-only-L libeditline)
LDLIBS    = $(shell pkg-config --libs-only-l libeditline)

Then simply type make, like above.

However, most .rpm based distributions pkg-config doesn't search in /usr/local anymore, so you need to call make like this:

PKG_CONFIG_LIBDIR=/usr/local/lib/pkgconfig make

Debian/Ubuntu based systems do not have this problem.

API

Here is the libeditline interfaces. It has a small compatibility layer to FSF readline, which may not be entirely up-to-date.

    /* Editline specific global variables. */
    int         el_no_echo;   /* Do not echo input characters */
    int         el_no_hist;   /* Disable auto-save of and access to history,
                               * e.g. for password prompts or wizards */
    int         el_hist_size; /* Size of history scrollback buffer, default: 15 */

    /* Editline specific functions. */
    char *      el_find_word     (void);
    void        el_print_columns (int ac, char **av);
    el_status_t el_ring_bell     (void);
    el_status_t el_del_char      (void);

    /* Callback function for key binding */
    typedef el_status_t el_keymap_func_t(void);

    /* Bind key to a callback, use CTL('f') to change Ctrl-F, for example */
    el_status_t el_bind_key            (int key, el_keymap_func_t function);
    el_status_t el_bind_key_in_metamap (int key, el_keymap_func_t function);

    /* For compatibility with FSF readline. */
    int         rl_point;
    int         rl_mark;
    int         rl_end;
    int         rl_inhibit_complete;
    char       *rl_line_buffer;
    const char *rl_readline_name;

    void (*rl_deprep_term_function)(void);
    void rl_deprep_terminal (void);
    void rl_reset_terminal  (const char *terminal_name);

    void rl_initialize   (void);
    void rl_uninitialize (void);                         /* Free all internal memory */

    void rl_save_prompt    (void);
    void rl_restore_prompt (void);
    void rl_set_prompt     (const char *prompt);

    void rl_clear_message         (void);
    void rl_forced_update_display (void);

    /* Main function to use, saves history by default */
    char *readline    (const char *prompt);

    /* Use to save a read line to history, when el_no_hist is set */
    void add_history  (const char *line);

    /* Load and save editline history from/to a file. */
    int read_history  (const char *filename);
    int write_history (const char *filename);

    /* Magic completion API, see examples/cli.c for more info */
    rl_complete_func_t    *rl_set_complete_func    (rl_complete_func_t *func);
    rl_list_possib_func_t *rl_set_list_possib_func (rl_list_possib_func_t *func);

    /* Alternate interface to plain readline(), for event loops */
    void rl_callback_handler_install (const char *prompt, rl_vcpfunc_t *lhandler);
    void rl_callback_read_char       (void);
    void rl_callback_handler_remove  (void);

Build & Install

Editline was originally designed for older UNIX systems and Plan 9. The current maintainer works exclusively on GNU/Linux systems, so it may use GCC and GNU Make specific extensions here and there. This is not on purpose and patches or pull requests to correct this are most welcome!

  1. Call ./autogen.sh if you build from git
  2. Configure editline with default features: ./configure
  3. Build the library and examples: make all
  4. Install using make install

The $DESTDIR environment variable is honored at install. For more options, see ./configure --help

Remember to run ldconfig after install to update the linker cache. If you've installed to a non-standard location (--prefix) you may also have to update your /etc/ld.so.conf, or use pkg-confg to build your application (above).

NOTE: RedHat/Fedora/CentOS and other .rpm-based distributions do not consider /usr/local as standard path anymore. So make sure to ./configure --prefix=/usr, otherwise the build system use the GNU default, which is /usr/local. The Debian based distributions, like Ubuntu, do not have this problem.

Origin & References

This line editing library was created by [Rich Salz][] and Simmule Turner and in 1992. It is distributed with a “C News-like” license, similar to the BSD license. Rich's current version is however under the Apache license. For details on the licensing terms of this version of the software, see License.

This version of the editline library was forked from the Minix 2 source tree and is not related to the similarily named NetBSD version that Jess Thrysøe disitributes to the world outside *BSD. The libraries have much in common, but the latter is heavily refactored and also relies on libtermcap (usually supplied by ncurses), whereas this library only uses termios from the standard C library.

Patches and bug fixes from the following forks, based on the original comp.sources.unix posting, have been merged:

The version numbering scheme today follows that of the Debian version, details available in the ChangeLog.md. The current maintainer was unaware of the Debian version for quite some time, so a different name and versioning scheme was used. In June 2009 this was changed to line up alongside Debian, with the intent is to eventually merge the efforts.

Outstanding issues are listed in the TODO.md file.