Custom Output

Implementing an AwkSink

Extend AwkSink and override print(...), printf(...), and getPrintStream():

public final class CollectingSink extends AwkSink {
    private final List<List<Object>> prints = new ArrayList<List<Object>>();
    private final PrintStream processOutput = System.out;

    public CollectingSink() {
        super(Locale.US);
    }

    @Override
    public void print(String ofs, String ors, String ofmt, Object... values) {
        prints.add(Arrays.asList(Arrays.copyOf(values, values.length)));
    }

    @Override
    public void printf(String ofs, String ors, String ofmt, String convfmt, String format, Object... values) {
        // store format + values however your application wants
    }

    @Override
    public PrintStream getPrintStream() {
        return processOutput;
    }

    public List<List<Object>> getCollectedPrints() {
        return prints;
    }
}

Sink print and printf Parameters

getPrintStream

getPrintStream() provides the PrintStream that receives the stdout of the processes a script spawns with system("...") or an output pipe (print ... | "cmd"). The default implementation discards it silently, so override this method — typically returning System.out or a stream of your own — in sinks that must capture subprocess output; see Subprocess Output. File redirection (print > "file") does not use this stream: it creates its own file-backed sink internally.

Special Filenames

The gawk special filenames^[2] are routed to the streams the run is configured with rather than to files of those names:

• print > "/dev/stdout" (and /dev/fd/1) writes to the sink, exactly like an unredirected print, so a script that writes there is captured by the host like any other output.
• print > "/dev/stderr" (and /dev/fd/2) writes to the stream passed to errorStream(PrintStream), which defaults to System.err.
• getline < "/dev/stdin" (and /dev/fd/0) reads the stream passed to input(...) — not the JVM's standard input, unless that is what the host supplied. When the run is fed with a structured InputSource instead of a stream, /dev/stdin falls back to System.in.

close() on these names never closes the host's streams.

Using a Custom Sink

Pass the sink to execute(...) on the builder:

Awk awk = new Awk();
CollectingSink sink = new CollectingSink();

awk.script("{ print $1, $2 }")
        .input("alpha beta\ngamma delta\n")
        .execute(sink);

// sink.getCollectedPrints() contains [[alpha, beta], [gamma, delta]]

Built-In Sink Implementations

Jawk provides three built-in AwkSink implementations:

• OutputStreamAwkSink renders output to an OutputStream or a PrintStream. This is the default behavior, and what execute(OutputStream) and execute(PrintStream) use.

• AppendableAwkSink renders output to any Appendable, such as a StringBuilder or a StringWriter.

• JavaStringFormatAwkSink renders printf/sprintf with Java's standard String.format(...) instead of AWK's formatting rules, giving scripts access to Java-only conversions (%,d grouping, %(d negative parentheses, %tY date/time, etc.) and faster formatting. Conversions must match the value's Java type: AWK integral numbers arrive as Long, other numbers as Double, and text as String, so %d requires an integral value and %f a floating-point one.

  awk.script("BEGIN { printf \"%,d\\n\", 1234567 }")
          .execute(new JavaStringFormatAwkSink(System.out));
  // prints: 1,234,567
  

The first two are also reachable through the AwkSink.from(...) factories, which accept an OutputStream, a PrintStream, or an Appendable. Every constructor and factory takes an optional Locale, and defaults to Locale.US without one.

With the Builder

When you use the AwkRunBuilder methods (execute(), execute(OutputStream), execute(Appendable)), the locale is taken automatically from AwkSettings. Set it once on the Awk instance:

Awk awk = new Awk();
awk.getSettings().setLocale(Locale.FRANCE);

// All execute() variants use the French locale for number formatting
String result = awk.script("BEGIN { print 3.14 }").execute();
// result == "3,14\n"

With a Custom AwkSink

When you pass an AwkSink to execute(AwkSink), the sink carries its own locale — AwkSettings is not involved. Specify the locale when constructing the sink:

AwkSink frenchSink = AwkSink.from(System.out, Locale.FRANCE);
awk.script("BEGIN { print 3.14 }").execute(frenchSink);

When extending AwkSink directly, pass the locale to the super(...) constructor:

public class MySink extends AwkSink {
    public MySink(Locale locale) {
        super(locale);
    }
    // ...
}