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szl is a tiny, embeddable scripting engine inspired by Tcl and shell. It's a
balanced mix of their key features: szl combines the simplicity of shell
scripting with the power of a dynamic, Tcl-like type system, minimalistic
syntax and programming language features missing in the shell, like exceptions
and OOP.

szl comes with a rich standard library that includes bindings for
permissively-licensed libraries. Therefore, it can run processes, parse text
with transparent Unicode support, manipulate data structures like dictionaries,
operate on binary data, interface with C code through scripts, multiplex
non-blocking I/O at scale, call REST APIs and much more, at a fraction of the
memory and size footprint of other scripting languages, while achieving
reasonable efficiency.

szl can be used both as a standalone (either interactive or non-interactive)
interpreter or as an integral part of other projects, via the libszl library. In
addition, the feature set and behavior of szl can be easily fine-tuned to meet
the size and memory consumption limitations under various usage scenarios and
hardware platforms.
  /                                   \
  | >>> $global msg {Hello, world!}   |
  | Hello, world!                     |
  | >>> $load zlib                    |
  | >>> $zlib.crc32 $msg              |
  | 3957769958                        |
  | >>> [$exec {uname -s}] read       |
  | Linux                             |
  | >>> [$open /bin/gunzip rb] read 9 |
  | #!/bin/sh                         |
  | >>> $map i [$range 1 4] {$+ $i 3} |
  | 4 5 6                             |

For more information, see the user manual at


On Debian ( based distributions:

  $ apt-get install git gcc meson zlib1g-dev libcurl4-gnutls-dev libarchive-dev
                    libssl-dev libffi-dev


  $ git clone --recursive
  $ cd szl
  $ meson build
  $ cd build
  $ ninja
  $ ninja install

By default, szl is built with core functionality built-in to the interpreter,
while a big part of the standard library resides in dynamically-loaded shared
objects. This way, the memory consumption of szl scripts that don't use the
entire standard library is lower.

However, in some use cases (for example, when szl is embedded into another
project), this is undesirable.

To build szl as a single executable file, with all extensions linked statically
into the interpreter:

  $ mesonconf -Dbuiltin_all=true

In addition, built-in extensions can be chosen individually, e.g.:

  $ mesonconf -Dwith_curl=builtin -Dwith_ffi=no


To embed szl into other projects, use the API defined in szl.h and link with

The size and performance of szl can be tuned using advanced build options:

  $ mesonconf -Duse_int=true

This build option replaces the large integer type used by szl to represent
integers, to the standard C int. This may improve performance under platforms
without native support for 64 bit integers, at the cost of a limited range of
valid integer values.

  $ mesonconf -Duse_float=false

This build option changes the precision of floating-point numbers in szl from
double to single precision. This may improve performance under platforms without
native support for double-precision floating point numbers, at the cost of

  $ mesonconf -Dwith_float=false

This build options disables support for floating-point arithmetic. This reduces
szl's size.

  $ mesonconf -Dwith_unicode=false

This build options disables support for Unicode strings and cancels szl's
internal distinction between encoded byte strings and arrays of Unicode code
points. This reduces szl's size and may improve performance with zero side
effects, if szl is guaranteed not to perform any sort of Unicode string slicing.


Support for dynamic loading of szl extensions can be disabled:

  $ mesonconf -Dwith_dl=false

When dynamic loading is disabled, szl will refuse to load extensions, unless
they are linked statically into the interpreter.

This way, a szl interpreter embedded into another program does not make it
vulnerable to dynamic loader hijacking (e.g. LD_LIBRARY_PATH) during extension


To run an interactive interpreter:

  $ szlsh

Or, to run a script:

  $ szl $path

Or, to run a one-liner:

  $ szl -c $snippet

Credits and Legal Information

szl is free and unencumbered software released under the terms of the MIT
license; see COPYING for the license text. For a list of its authors and
contributors, see AUTHORS.

The ASCII art logo at the top was made using FIGlet (