docs: add example to count ERROR lines in a log file (#236)

examples/app.log

@@ -0,0 +1,6 @@
+2026-06-19 12:00:00 [INFO] Starting application...
+2026-06-19 12:01:05 [WARN] Low memory warning
+2026-06-19 12:02:10 [ERROR] Database connection failed
+2026-06-19 12:03:15 [INFO] Retrying database connection...
+2026-06-19 12:04:20 [ERROR] Retries exhausted. Could not connect to database.
+2026-06-19 12:05:00 [INFO] Shutting down application.

examples/count_errors.go

@@ -0,0 +1,32 @@
+//go:build ignore
+
+// This program reads a log file, filters only the lines containing "ERROR", and prints the count of those lines.
+// It uses the github.com/bitfield/script library to handle the file reading, matching, and counting.
+//
+// Equivalent shell command:
+// grep ERROR app.log | wc -l
+
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/bitfield/script"
+)
+
+func main() {
+	// Check if examples/app.log exists, otherwise fallback to app.log.
+	logFile := "examples/app.log"
+	if _, err := os.Stat(logFile); os.IsNotExist(err) {
+		logFile = "app.log"
+	}
+
+	count, err := script.File(logFile).Match("ERROR").CountLines()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error reading log file: %v\n", err)
+		os.Exit(1)
+	}
+
+	fmt.Printf("Number of ERROR lines: %d\n", count)
+}

examples/filter_csv.go

@@ -0,0 +1,31 @@
+//go:build ignore
+
+// This program reads a CSV file containing server names and their status (comma separated),
+// filters only the lines where the status is "DOWN", and prints the name of each such server (first column).
+// It uses the github.com/bitfield/script library to handle the file reading, matching, replacing, and filtering.
+//
+// Equivalent shell command:
+// grep DOWN servers.csv | cut -d, -f1
+
+package main
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/bitfield/script"
+)
+
+func main() {
+	// Check if examples/servers.csv exists, otherwise fallback to servers.csv.
+	csvFile := "examples/servers.csv"
+	if _, err := os.Stat(csvFile); os.IsNotExist(err) {
+		csvFile = "servers.csv"
+	}
+
+	_, err := script.File(csvFile).Match("DOWN").Replace(",", " ").Column(1).Stdout()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error reading CSV file: %v\n", err)
+		os.Exit(1)
+	}
+}

examples/servers.csv

@@ -0,0 +1,5 @@
+server1,UP
+server2,DOWN
+server3,DOWN
+server4,UP
+server5,DOWN