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Bash interpreter

A proof of concept to see how feasible a bash interpreter for the JVM would/could be.

Current status

Very early prototype built on top of the libbash ANTLR grammar, aims to implement basic stuff. The grammar provides an AST.

Test drive

Interactive repl can trivially be started:

mvn test -Prepl
...
> a=4
> echo $a
4
> echo $((a + 4))
8
> for((i=1;i<=20;i++)); do echo $i;done | grep 1
1
10
11
12
13
14
15
16
17
18
19
> echo $i
21
>

Anything that does not work provide the abstract syntax tree portion not implemented:

> ls | more
java.lang.UnsupportedOperationException: Tree PIPE not yet implemented:
tree: PIPE
  tree: COMMAND
    tree: STRING
      tree: NAME
  tree: COMMAND
    tree: STRING
      tree: NAME

	at org.crashub.bash.Script._LIST(Script.java:417)
	at org.crashub.bash.Script.execute(Script.java:64)
	at org.crashub.bash.Repl.main(Repl.java:40)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:606)
	at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:297)
	at java.lang.Thread.run(Thread.java:744)

Implementing missing features

We use test driven development for implementing the interpreter.

Add a test that make the execution fail

public void testARITHMETIC_EXPRESSION_LESS_THAN() throws Exception {
  assertEquals("0", eval("$((2<2))\n"));
  assertEquals("1", eval("$((2<3))\n"));
  assertEquals("0", eval("$((3<2))\n"));
}

Execute the tests

java.lang.UnsupportedOperationException: Tree LESS_THAN not yet implemented:
tree: LESS_THAN
  tree: DIGIT
  tree: DIGIT
        at org.crashub.bash.Script.assertTree(Script.java:90)
        at org.crashub.bash.Script._ARITHMETIC_EXPRESSION(Script.java:234)
        at org.crashub.bash.Script._STRING(Script.java:143)
        at org.crashub.bash.Script._VARIABLE_DEFINITIONS(Script.java:125)
        at org.crashub.bash.Script._COMMAND(Script.java:386)
        at org.crashub.bash.Script._LIST(Script.java:403)
        at org.crashub.bash.Script.execute(Script.java:64)
        at org.crashub.bash.TestScript.eval(TestScript.java:24)
        at org.crashub.bash.TestScript.eval(TestScript.java:19)
        at org.crashub.bash.TestScript.testARITHMETIC_EXPRESSION_LESS_THAN(TestScript.java:88)

Implement the missing code

case java_libbashParser.LESS_THAN:
  return l < r ? 1 : 0;

Wanna help ?

Sure there are plenty of things to do, get in touch with me