Compile, Eval, and Reuse

Simple Expression Evaluation

eval() is the direct path when you want the value of an expression rather than the printed output of a full AWK program.

Awk awk = new Awk();
Object value = awk.eval("$2", "alpha beta");
// value = "beta"

Structured input works the same way:

Awk awk = new Awk();
InputSource source = new TableInputSource(
        Collections.singletonList(Arrays.asList("alpha", "beta")));
Object value = awk.eval("$2", source);
// value = "beta"

Each high-level Awk.eval(...) call creates, prepares, uses, and closes a fresh runtime, so evaluations stay isolated from one another.

Precompile an Expression

When the same expression runs many times, compile it once and reuse it:

AwkSettings settings = new AwkSettings();
settings.setFieldSeparator(",");

Awk awk = new Awk(settings);
AwkExpression expression = awk.compileExpression("$2");

Object first = awk.eval(expression, "alpha,beta");
Object second = awk.eval(expression, "left,right");

Compile a Full Program

For full AWK programs, compile to AwkProgram and then run that compiled program with the input and output you want:

Awk awk = new Awk();
AwkProgram program = awk.compile("{ print $1 }");

awk.script(program)
        .input(new ByteArrayInputStream("alpha beta\n".getBytes(StandardCharsets.UTF_8)))
        .execute(System.out);

This keeps compilation and execution separate, which is useful when the same AWK program is reused across multiple inputs.

Compilation settings matter here. For example, gawk-style arrays of arrays (a[i][j]) are accepted by default, but you can disable that compile-time mode before compiling. When disabled, Jawk also rejects subarray operands in array-only positions such as split(..., a[i]) or for (k in a[i]):

AwkSettings settings = new AwkSettings();
settings.setAllowArraysOfArrays(false);

Awk awk = new Awk(settings);
AwkProgram program = awk.compile("{ print a[1,2] }");

Choosing the Right Reuse Strategy

• Use eval(String...) when the expression is cheap and called only occasionally.
• Use AwkExpression plus eval(...) when one expression is reused across many records.
• Use AwkProgram plus script(program).execute(...) when a whole AWK program is reused.
• Use AVM when you want to keep one runtime alive across several calls. See the Advanced Runtime^[1] guide for AVM-level reuse patterns.

See Also

• Java Quickstart^[2]
• Variables and Arguments^[3]
• Structured Input^[4]
• Custom Output^[5]
• Advanced Runtime^[1]