commit 73b0cb124928ee6838cfe1803e5d78df44892779
Author: Tordarus <tordarus@protonmail.com>
Date:   Fri Aug 20 23:37:18 2021 +0200

    initial commit

diff --git a/format b/format
new file mode 100755
index 0000000..e913be6
Binary files /dev/null and b/format differ
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..7bc484e
--- /dev/null
+++ b/main.go
@@ -0,0 +1,73 @@
+package main
+
+import (
+	"bufio"
+	"flag"
+	"fmt"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+var (
+	input         = flag.String("i", "^.*?$", "input pattern")
+	output        = flag.String("o", "{0}", "output pattern")
+	keepUnmatched = flag.Bool("k", false, "keep unmatched lines")
+
+	replacePattern = regexp.MustCompile("\\{(\\d+)(?::(.*?))?\\}")
+)
+
+func main() {
+	flag.Parse()
+
+	pattern, err := regexp.Compile(*input)
+	if err != nil {
+		panic(err)
+	}
+
+	r := bufio.NewReader(os.Stdin)
+	for line, err := r.ReadString('\n'); err == nil; line, err = r.ReadString('\n') {
+		line = line[:len(line)-1]
+		matches := pattern.FindStringSubmatch(line)
+
+		fmt.Println(matches)
+
+		if len(matches) == 0 {
+			if *keepUnmatched {
+				fmt.Println(line)
+			}
+			continue
+		}
+
+		fmt.Println(replaceVars(*output, matches...))
+	}
+}
+
+func replaceVars(format string, vars ...string) string {
+	replacements := replacePattern.FindAllStringSubmatch(format, -1)
+
+	for _, replacement := range replacements {
+		rplStr := replacement[0]
+		varIndex, _ := strconv.Atoi(replacement[1])
+		rplFmt := replacement[2]
+
+		// default format if not specified by user
+		if rplFmt == "" {
+			rplFmt = "%s"
+		}
+
+		if strings.HasSuffix(rplFmt, "d") { // replace integers
+			value, _ := strconv.ParseInt(vars[varIndex], 10, 64)
+			format = strings.Replace(format, rplStr, fmt.Sprintf(rplFmt, value), 1)
+		} else if strings.HasSuffix(rplFmt, "f") { // replace floats
+			value, _ := strconv.ParseFloat(vars[varIndex], 64)
+			format = strings.Replace(format, rplStr, fmt.Sprintf(rplFmt, value), 1)
+		} else { // replace strings
+			format = strings.Replace(format, rplStr, fmt.Sprintf(rplFmt, vars[varIndex]), 1)
+		}
+
+	}
+
+	return format
+}