regexFirstGroup return first group from regexp, useful with .env file… (#895)

* regexFirstGroup return first group from regexp, useful with .env files and another config files

* documentation about regexFirstGroup and example

* modify func regexFirstGroup to findStringSubmatch, return all the submatchs from regex

* func findStringSubmatch(), returns map[string]interface{} for use with get and named parenthesized subexpressions or stringfied array string

Author: alexandregz

docs/gossfile.md

@@ -918,6 +918,31 @@ Available functions:
     `toUpper`
     :   Changes piped input to UPPERCASE
 
+       
+    `findStringSubmatch regex string`
+    :   Returns map[string]interface{} with the names of the parenthesized subexpressions, like `(?P<first>[a-z])`
+        
+        {{ $regexDBrc := "\\'mysql:\\/\\/(?P<login>[a-z0-9]+):(?P<password>[a-z0-9]+)@localhost\\/(?P<database>roundcube_[a-z0-9]+)\\';"}}
+        
+        {{ $rcConf := readFile /home/user/roundcube/config.inc.php | findStringSubmatch $regexDBrc }}
+        {{ $UserDBrc := get $rcConf "login" }}
+        {{ $PassDBrc  := get $rcConf "password" }}
+        {{ $DBrc := get $rcConf "database" }}
+
+    If not exists named parenthesized subexps, returns stringfied array string:
+
+        {{ $regexDBrc := "\\'mysql:\\/\\/([a-z0-9]+):([a-z0-9]+)@localhost\\/(roundcube_[a-z0-9]+)\\';"}}
+        
+        {{ $rcConf := readFile /home/user/roundcube/config.inc.php | findStringSubmatch $regexDBrc }}
+        {{ $UserDBrc := get $rcConf "1" }}
+        {{ $PassDBrc  := get $rcConf "2" }}
+        {{ $DBrc := get $rcConf "3" }}
+
+    NOTE: stringfied string array begins with "1" ("0" is all the string matched)
+
+        
+
+
 !!! warning
 
     gossfiles containing text/template `{{}}` controls will no longer work with `goss add/autoadd`.

template.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"regexp"
+	"strconv"
 	"strings"
 	"text/template"
 
@@ -76,11 +77,37 @@ func regexMatch(re, s string) (bool, error) {
 	return compiled.MatchString(s), nil
 }
 
+// return named parenthesized subexpresions, if received, or stringfied (Sprig "get" need strings) keys like array
+func findStringSubmatch(pattern, input string) map[string]interface{} {
+	re := regexp.MustCompile(pattern)
+	els := re.FindStringSubmatch(input)
+
+	elsMap := make(map[string]interface{})
+	elsMapNamed := make(map[string]interface{})
+
+	// create always elsMaps but returns elsMapNamed if exists named parenthesized subexps
+	for i := 0; i < len(els); i++ {
+		// convert i to string according returned (https://github.com/goss-org/goss/pull/895#issuecomment-2075716706)
+		elsMap[strconv.Itoa(i)] = els[i]
+
+		if re.SubexpNames()[i] != "" {
+			elsMapNamed[re.SubexpNames()[i]] = els[i]
+		}
+	}
+
+	// returns elsMapNamed if exists named parenthesized subexps
+	if len(elsMapNamed) > 0 {
+		return elsMapNamed
+	}
+	return elsMap
+}
+
 var funcMap = template.FuncMap{
-	"mkSlice":    mkSlice,
-	"readFile":   readFile,
-	"getEnv":     getEnv,
-	"regexMatch": regexMatch,
-	"toUpper":    strings.ToUpper,
-	"toLower":    strings.ToLower,
+	"mkSlice":            mkSlice,
+	"readFile":           readFile,
+	"getEnv":             getEnv,
+	"regexMatch":         regexMatch,
+	"toUpper":            strings.ToUpper,
+	"toLower":            strings.ToLower,
+	"findStringSubmatch": findStringSubmatch,
 }