treat data until EOF as new line and parse escape sequences

esc_seq.go

@@ -0,0 +1,14 @@
+package main
+
+import "strings"
+
+var EscSeqReplacer = strings.NewReplacer(
+	`\\`, `\`,
+	`\n`, "\n",
+	`\t`, "\t",
+	`\f`, "\f",
+	`\r`, "\r",
+	`\v`, "\v",
+	`\b`, "\b",
+	`\a`, "\a",
+)

main.go

@@ -10,11 +10,12 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	"unicode/utf8"
 )
 
 var (
 	// regex with sub groups
-	input = flag.String("i", "^.*?$", "input pattern")
+	input = flag.String("i", `^(.|\n)*?$`, "input pattern")
 
 	// format string with {0} as placeholders
 	// {0} always matches the whole line
@@ -58,8 +59,9 @@ func main() {
 		panic(err)
 	}
 
+	escapedOutput := EscSeqReplacer.Replace(*output)
+
 	for line := range readLines(os.Stdin) {
-		line = line[:len(line)-1]
 		matches := pattern.FindStringSubmatch(line)
 
 		if len(matches) == 0 {
@@ -69,7 +71,7 @@ func main() {
 			continue
 		}
 
-		fmt.Println(replaceVars(*output, matches...))
+		fmt.Println(replaceVars(escapedOutput, matches...))
 	}
 }
 
@@ -85,16 +87,30 @@ func readLines(r io.Reader) <-chan string {
 			var line string
 			var err error
 			lines := make([]string, 0, *lineParseAmount)
-			for line, err = r.ReadString('\n'); err == nil; line, err = r.ReadString('\n') {
+			for line, err = r.ReadString('\n'); ; line, err = r.ReadString('\n') {
+				if rn, size := utf8.DecodeLastRuneInString(line); rn == '\n' {
+					line = line[:len(line)-size]
+				}
+
 				lines = append(lines, line)
-				if len(lines) == cap(lines) {
+
+				// stop reading as soon as lineParseAmount is reached or an error occured (most likely EOF)
+				if len(lines) == cap(lines) || err != nil {
 					break
 				}
 			}
+
+			linesCombined := strings.Join(lines, "\n")
+
+			// use data as line if reading was successfull or EOF has been reached
+			// in the latter case: only use data if something could be read until EOF
+			if err == nil || err == io.EOF && linesCombined != "" {
+				out <- linesCombined
+			}
+
 			if err != nil {
 				return
 			}
-			out <- strings.Join(lines, "")
 		}
 	}(ch, r)