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An IRC client written in bash

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m birch

An IRC client written in bash.



* Full power of readline for input and keybindings. 

This is thanks to bash's read -e. Birch will read a readline based configuration file from the environment variable '$BIRCH_INPUTRC' which allows you to customize everything.

  • Tab completion of nicks and channels.

    Bash hardcodes read -e tab completion to the file based one. This works fine for channel completion as each channel log is stored in a file anyway. For nick completion, birch will create an empty file for each nick in the channel. Hey, it works.

  • Unique (or semi-unique) nick colors.

    All nicks are colored based on their length. The length is mapped to a color between 1 and 6 which is then used as input for '\033[1;3m'.

Caveats (or limitations)

* Nick column is fixed and truncated to 10 columns wide.

This is something fixable down the line. It merely serves to simplify the alignment of messages into two columns (nick and messages).

  • Lines are word-wrapped to a fixed 60 columns.

    This is also fixable down the line though a lot more painful than the nick column issue. POSIX fold is used to achieve the word wrapping but doesn't take into account non-printable characters and unicode.

    What this means is that wrapping will always be a little off as escape sequences, IRC formatting and unicode will throw out all attempts at calculating the "visible" line length.

    It's an interesting problem to solve. I've made a myriad of attempts at writing a suitable function in bash though they're all too slow (as expected!).

  • No automatic server reconnect.

    This should be fairly easy to fix though I need to figure out the best way of doing so.

  • No SSL (sadly).

    The network connection is through bash's builtin /dev/tcp feature which doesn't allow for SSL.

  • Interesting facts

    * Connection to the IRC server happens without external

    Bash support network connections via two virtual device directories it "creates" in '/dev/'.

    '/dev/tcp/host/port' and '/dev/udp/host/port'.

    I don't exactly know why these were implemented as it's a crazy feature for a shell to have. I haven't seen them widely used either.

  • The input loop and listener loop can't communicate.

    Birch utilizes two loops to work. One for the input and an additional loop to listen to incoming IRC messages.

    When something is run asynchronously in bash with '&', it runs in a subshell (a second bash process).

    What this means is that the async code can't communicate with the blocking code. Any variables set in the input loop once both loops are running won't be visible in the async listener loop to give an example.

    To work around this birch utilizes files for IPC between the two. The current channel is communicated by maintaining a symlink and checking its target where needed.

    Example: .c -> '#current_channel'

  • This was HARD.

    Trying to make the input prompt and async listener (which spits out messages to the terminal) play nice took a lot of work.

    As birch implements a TUI manually we're dealing with bare escape sequences to tie everything together.

    When a message needs to be printed, the cursor must move from the input prompt to the output area, print the message and finally return back to the input prompt.

    All of this must happen just right to ensure that this series of cursor movements doesn't end up mangling the display of the interface.

    Birch has gone through a lot of rewrites to get this perfect. Fun fact: The older revisions read input char by char and implemented a lot of readline by hand.

  • Usage


    -s -c -u -p -U -P -x

    -h (help) -v (version)


    • bash 4+
    • POSIX compatible


    Ctrl+n - Next buffer.
    Ctrl+p - Previous buffer.
    Tab    - Completion of nicks and channels.

    Further, all readline keybindings are available for use. See the readline or bash manpages for a list of these.

    Keybindings to birch may also be set via a .inputrc file. Which can be configured by setting $BIRCH_INPUTRC.

    (BIRCH_INPUTRC=/path/to/birch-inputrc birch)



    /join - Join a channel. /part - Leave a channel. /quit - Quit out of birch.


    /msg - Message a user. /me - Send an action.


    /next - Next buffer. /prev - Previous buffer. / - Buffer by number (0 indexed).


    /nick - Change nickname. /names - Display all nicks in channel. /topic - Display channel topic. /away - Set afk message. /raw - Send a raw IRC message.


    (These are environment variables.)

    Set the formatting of the tab line's selected item.

    This defaults to reverse video.


    The path to a readline based .inputrc file to change

    birch's input settings.



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