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how-to-run-abs-code.md

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How to run ABS code

In order to run programs written in abs, you can simply download the latest release of ABS from Github, and dump the ABS executable in your PATH. Windows, OSX and a few Linux flavors are supported.

We also provide a 1-command installer that should work across platforms:

bash <(curl https://www.abs-lang.org/installer.sh)

and will download the abs executable in your current directory -- again, we recommend to move it to your $PATH.

Afterwards, you can run ABS scripts with:

$ abs path/to/scripts.abs

You can also run an executable abs script directly from bash using a bash shebang line at the top of the script file.

In this example the abs executable is linked to /usr/local/bin/abs and the abs script ~/bin/remote.abs has its execute permissions set.

$ cat ~/bin/remote.abs
#! /usr/local/bin/abs
# remote paths are <target>:<path> 
from_path = arg(2) 
to_path = arg(3)
if ! (from_path && to_path) {
    if ! from_path {from_path = "<missing>"}
    if ! to_path {to_path = "<missing>"}
    echo("FROM: %s, TO: %s", from_path, to_path)
    exit(1)
}
...
# the executable abs script above is in the PATH at ~/bin/remote.abs
$ remote.abs
FROM: <missing>, TO: <missing>

Scripts do not have to have a specific extension, although it's recommended to use .abs as a convention.

A bit lost right now? We'd suggest to clone ABS' main repository as you can already start testing some code with the scripts in the examples directory.

REPL

If you want to get a more live feeling of ABS, you can also simply run the interpreter; without any argument. It will launch ABS' REPL, and you will be able to test code on the fly:

$ abs
Hello there, welcome to the ABS programming language!
Type 'quit' when you're done, 'help' if you get lost!
⧐  ip = `curl icanhazip.com`
⧐  ip.ok
true
⧐  ip()
ERROR: not a function: STRING
⧐  ip
94.204.178.37

REPL Command History

Interactive REPL sessions can restore and save the command history to a history file containing a maximum number of command lines.

The prompt live history is restored from the history file when the REPL starts and then saved again when the REPL exits. This way you can navigate through the command lines from your previous sessions by using the up and down arrow keys at the prompt.

  • Note well that the live prompt history will show duplicate command lines, but the saved history will only contain a single command when the previous command and the current command are the same.

The history file name and the maximum number of history lines are configurable through

  1. the ABS environment (set by the ABS init file; see below)
  2. the OS environment
  3. The default values are ABS_HISTORY_FILE="~/.abs_history" and ABS_MAX_HISTORY_LINES=1000.
  • If you wish to suppress the command line history completely, just set ABS_MAX_HISTORY_LINES=0. In this case the history file will not be created.

For example:

$ export ABS_HISTORY_FILE="~/my_abs_hist"
$ export ABS_MAX_HISTORY_LINES=500
$ abs
Hello user, welcome to the ABS (1.1.0) programming language!
Type 'quit' when you are done, 'help' if you get lost!
⧐  pwd()
/home/user/git/abs
⧐  cd()
/home/user
⧐  echo("hello")
hello
⧐  quit
Adios!

$ cat ~/my_abs_hist`; echo
pwd()
cd()
echo("hello")
$

ABS Init File

When the ABS interpreter starts running, it will load an optional ABS script as its init file. The ABS init file path can be configured via the OS environment variable ABS_INIT_FILE. The default value is ABS_INIT_FILE=~/.absrc.

If the ABS_INIT_FILE exists, it will be evaluated before the interpreter begins in both interactive REPL or script modes. The result of all expressions evaluated in the init file become part of the ABS global environment which are available to command line expressions or script programs.

Also, note that the ABS_INTERACTIVE global environment variable is pre-set to true or false so that the init file can determine which mode is running. This is useful if you wish to set the ABS REPL command line prompt or history configuration variables in the init file. This will preset the prompt and history parameters for the interactive REPL (see REPL Command History above).

Configuring the ABS REPL Command Line Prompt

The ABS REPL command line prompt may be configured at start up using ABS_PROMPT_LIVE_PREFIX and ABS_PROMPT_PREFIX variables from either the ABS or OS environments. The default values are ABS_PROMPT_LIVE_PREFIX=false and ABS_PROMPT_PREFIX="⧐ ".

REPL "static prompt" mode will be configured if ABS_PROMPT_PREFIX contains no live prompt template string or if ABS_PROMPT_LIVE_PREFIX=false. The static prompt will be the value of the ABS_PROMPT_PREFIX string (if present) or the default prompt "⧐ ". Static prompt mode is the default for the REPL.

REPL "live prompt" mode follows the current working directory set by cd() when both ABS_PROMPT_LIVE_PREFIX=true and the ABS_PROMPT_PREFIX variable contains a live prompt template string.

A live prompt template string may contain the following named placeholders:

  • {user}: the current userId
  • {host}: the local hostname
  • {dir}: the current working directory following cd()

For example, you can create a bash-style live prompt:

$ cat ~/.absrc
# ABS init script ~/.absrc 
# For interactive REPL, override default prompt, history filename and size
if ABS_INTERACTIVE {
    ABS_PROMPT_LIVE_PREFIX = true
    ABS_PROMPT_PREFIX = "{user}@{host}:{dir}$ "
    ABS_HISTORY_FILE = "~/.abs_hist"
    ABS_MAX_HISTORY_LINES = 500
}
$ abs
Hello user, welcome to the ABS (1.1.0) programming language!
Type 'quit' when you are done, 'help' if you get lost!
user@hostname:~/git/abs$ cwd = cd()
user@hostname:~$ `ls .absrc`
.absrc
user@hostname:~$

Also see a template ABS Init File at examples.

Why is abs interpreted?

ABS' goal is to be a portable, pragmatic, concise, simple language: great performance comes second.

With this in mind, we made a deliberate choice to avoid compiling ABS code, as it would require additional complexity in the codebase, with very little benefits. Tell us, when was the last time you were interested in how many milliseconds it took to run a Bash script?

Next

That's about it for this section!

You can now head over to read about ABS's syntax, starting with assignments!