Package: libdash
libdashis a fork of the Linux Kernel'sdashshell that builds a linkable library with extra exposed interfaces. The primary use of libdash is to parse shell scripts, but it could be used for more.The Python bindings are packaged as thelibdashPyPi package.The OCaml bindings---packaged as thelibdashOPAM package---include two executables,shell_to_jsonandjson_to_shell, which let you conveniently parse POSIX shell scripts into a JSON AST.What are the dependencies?The C code for dash should build on a wide variety of systems; it requireslibtoolandautotools(aclocal,autoheader,automake,autoconf). The library may not build on platforms with esoteric linkers; it's been tested on macOS and Linux.The Python and OCaml bindings depend on being able to build the C code. Seelibdash.opamfor details on the OCaml code's dependencies, which includes the build-time external dependencies. Python wheels have no need for these build-time dependencies, but building from a Python source distribution will only succeed whenlibtoolandautotoolsare present.The CI scripts (in.github/workflows/build.yml) give build details.How to buildlibdashfrom sourcePythonRunpython3 setup.py install. On macOS, you must first install the build dependencies viabrew install libtool autoconf automake.You can test the Python bindings by running:cd python; make testOCamlInstall the OPAM file:opam pin add .oropam install .. This will build the OCaml library and install it in your OPAM repository. There are tests in another directory; they will only build when libdash is actually installed.You can test the OCaml bindings by running:cd ocaml; make testTestingThe tests usetest/round_trip.shto ensure that every tester file intest/testsround-trips correctly through parsing and pretty printing.Additionally, you can run tests that compare the OCaml and Python implementations (after you've installed them both):cd test; makeHow to use the parserFor Python, seepython/rt.py, an example tool that does a round-trip: shell syntax to AST back to shell syntax.For OCaml, seeocaml/shell_to_json.ml, a tool that parses shell syntax and produces JSON (using theatdgenbindings).The ideal low-level interface to use isparsecmd_safeinparser.c; you'll need to ensure that dash's initialization routines have been called and that the stack marks are managed correctly. Parsing the POSIX shell is a complicated affair: beyond the usual locale issues, aliases affect the lexer, so one must usesetaliasandunaliasto manage any aliases that ought to exist.How work with the parsed nodesThe general AST is described innodes.h. There are some tricky invariants around the precise formatting of control codes; the OCaml code shows some examples of working with theargsfields inocaml/ast.ml, which converts the C AST to an OCaml AST.The OCaml toolsshell_to_jsonandjson_to_shellwill produce JSON ASTs, allowing you to work with these ASTs in any language.Pretty printingThe pretty printer does its best to produce valid shell scripts, but it's possible to manually construct AST nodes that don't directly correspond to valid scripts.For example, the Python AST[[['Q', [['C', 34]]]]]represents a quoted field containing a double quote character. Translated literally, this would yield the string""", which is not a valid shell script. The pretty printer will instead automatically escape the inner quote, rendering"\"".While the printer tries to get things right either way, you should use escapes to signal to the printer when to escape: you should use the Python AST[[['Q', [['E', 34]]]]]to mark the inner double quote as escaped.Known issuesWe currently do not escape the character!(exclamation point). In an interactive shell,!is likely treated as a history substitution (and so should be escaped), but in a non-interactive shell,!is treated normally. We currently cater to non-interactive shells; eventually this behavior will be controllable.