Add query-only mode for piping results to visidata/pspg/less

Query mode auto-activates when destination flags are omitted, outputting CSV/TSV to stdout for interactive data exploration of DB2 iSeries queries.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

jrunner/src/main/java/jrunner/jrunner.java

@@ -27,6 +27,8 @@ public class jrunner {
         String nr = "";
         String nc = "";
         String nl = "\n";
+        Boolean queryMode = false;
+        String outputFormat = "csv";
         String msg = "";
         Connection scon = null;
         Connection dcon = null;
@@ -50,6 +52,7 @@ public class jrunner {
         msg = msg + nl + "-dt        fully qualified name of destination table";
         msg = msg + nl + "-t         trim text";
         msg = msg + nl + "-c         clear target table";
+        msg = msg + nl + "-f         output format (csv, tsv, table, json) - default: csv";
         msg = msg + nl + "--help     info";
 
         //---------------------------------------parse args into variables-------------------------------------------------
@@ -104,6 +107,9 @@ public class jrunner {
                 case "-c":
                     clear = true;
                     break;
+                case "-f":
+                    outputFormat = args[i+1].toLowerCase();
+                    break;
                 case "-v":
                     System.out.println(msg);
                     return;
@@ -127,6 +133,15 @@ public class jrunner {
             }
         }
 
+        // Detect query mode when destination flags are not provided
+        queryMode = dcu.isEmpty() && dcn.isEmpty() && dcp.isEmpty() && dt.isEmpty();
+
+        if (queryMode) {
+            System.err.println("------------query mode------------------------------------");
+            System.err.println("source db uri:        " + scu);
+            System.err.println("source db username:   " + scn);
+            System.err.println("output format:        " + outputFormat);
+        } else {
             System.out.println("------------db info---------------------------------------");
             System.out.println("source db uri:        " + scu);
             System.out.println("source db username:   " + scn);
@@ -136,6 +151,7 @@ public class jrunner {
             System.out.println(sq);
             System.out.println("------------destination table-----------------------------");
             System.out.println(dt);
+        }
 
         //return;
 
@@ -149,7 +165,11 @@ public class jrunner {
 
         //-------------------------------------------establish connections-------------------------------------------------
         //source database
+        if (queryMode) {
+            System.err.println("------------open database connection---------------------");
+        } else {
             System.out.println("------------open database connections---------------------");
+        }
         try {
             scon = DriverManager.getConnection(scu, scn, scp);
         } catch (SQLException e) {
@@ -159,6 +179,7 @@ public class jrunner {
         } 
         System.out.println(" ✅ source database");
         //destination database
+        if (!queryMode) {
             try {
                 dcon = DriverManager.getConnection(dcu, dcn, dcp);
             } catch (SQLException e) {
@@ -167,6 +188,7 @@ public class jrunner {
                 System.exit(0);
             }
             System.out.println(" ✅ destination database");
+        }
         //----------------------------------------open resultset------------------------------------------------------------
         try {
             stmt = scon.createStatement();
@@ -204,7 +226,7 @@ public class jrunner {
             System.exit(0);
         }
         //-------------------------clear the target table if requeted----------------------------------------------------
-        if (clear) {
+        if (!queryMode && clear) {
             System.out.println("------------clear target table----------------------------");
             sql = "DELETE FROM " + dt;
             try {
@@ -217,6 +239,15 @@ public class jrunner {
                 System.exit(0);
             }
         }
+        if (queryMode) {
+            //-------------------------------output query results--------------------------------------------------------
+            try {
+                outputQueryResults(rs, cols, dtn, outputFormat);
+            } catch (SQLException e) {
+                e.printStackTrace();
+                System.exit(0);
+            }
+        } else {
             System.out.println("------------row count-------------------------------------");
             //-------------------------------build & execute sql-------------------------------------------------------------
             try {
@@ -354,22 +385,107 @@ public class jrunner {
                 e.printStackTrace();
                 System.exit(0);
             }
+        }
         //System.out.println(sql);
 
         //---------------------------------------close connections--------------------------------------------------------
         try {
             scon.close();
+            if (!queryMode && dcon != null) {
                 dcon.close();
+            }
         } catch (SQLException e) {
             System.out.println("issue closing connections");
             e.printStackTrace();
         }
+        if (!queryMode) {
             System.out.println(" rows written");
             tsEnd = Timestamp.from(Instant.now());
             System.out.println(tsStart);
             System.out.println(tsEnd);
+        }
         //long time = Duration.between(tsStart, tsEnd).toMillis();
         //System.out.println("time elapsed: " + time);
         System.out.println();
     }
+
+    private static void outputQueryResults(ResultSet rs, int cols, String[] dtn, String format) throws SQLException {
+        switch (format) {
+            case "csv":
+                outputCSV(rs, cols);
+                break;
+            case "tsv":
+                outputTSV(rs, cols);
+                break;
+            case "table":
+                System.err.println("Table format not yet implemented, defaulting to CSV");
+                outputCSV(rs, cols);
+                break;
+            case "json":
+                System.err.println("JSON format not yet implemented, defaulting to CSV");
+                outputCSV(rs, cols);
+                break;
+            default:
+                System.err.println("Unknown format: " + format + ", defaulting to CSV");
+                outputCSV(rs, cols);
+                break;
+        }
+    }
+
+    private static void outputCSV(ResultSet rs, int cols) throws SQLException {
+        // Print header row
+        for (int i = 1; i <= cols; i++) {
+            if (i > 1) System.out.print(",");
+            System.out.print(escapeCSV(rs.getMetaData().getColumnName(i)));
+        }
+        System.out.println();
+
+        // Print data rows
+        while (rs.next()) {
+            for (int i = 1; i <= cols; i++) {
+                if (i > 1) System.out.print(",");
+                String value = rs.getString(i);
+                if (rs.wasNull() || value == null) {
+                    // Empty field for NULL
+                } else {
+                    System.out.print(escapeCSV(value));
+                }
+            }
+            System.out.println();
+        }
+    }
+
+    private static void outputTSV(ResultSet rs, int cols) throws SQLException {
+        // Print header row
+        for (int i = 1; i <= cols; i++) {
+            if (i > 1) System.out.print("\t");
+            System.out.print(escapeTSV(rs.getMetaData().getColumnName(i)));
+        }
+        System.out.println();
+
+        // Print data rows
+        while (rs.next()) {
+            for (int i = 1; i <= cols; i++) {
+                if (i > 1) System.out.print("\t");
+                String value = rs.getString(i);
+                if (rs.wasNull() || value == null) {
+                    // Empty field for NULL
+                } else {
+                    System.out.print(escapeTSV(value));
+                }
+            }
+            System.out.println();
+        }
+    }
+
+    private static String escapeCSV(String value) {
+        if (value.contains(",") || value.contains("\"") || value.contains("\n") || value.contains("\r")) {
+            return "\"" + value.replaceAll("\"", "\"\"") + "\"";
+        }
+        return value;
+    }
+
+    private static String escapeTSV(String value) {
+        return value.replaceAll("\t", " ").replaceAll("\n", " ").replaceAll("\r", " ");
+    }
 }