- [+] add substr template function

Author: suntong

cmd/easygen/main.go

@@ -41,8 +41,8 @@ import (
 
 var (
 	progname = "easygen"
-	version  = "4.1.0"
-	date     = "2019-06-18"
+	version  = "4.1.01"
+	date     = "2020-07-26"
 )
 
 ////////////////////////////////////////////////////////////////////////////

template.go

@@ -101,6 +101,7 @@ var egFuncMap = FuncMap{
 
 	// == my added functions
 	"ENV":         os.Getenv,
+	"substr":      Substr,
 	"coalesce":    coalesce,
 	"quote4shell": quote4shell,
 

tf-strings.go

@@ -1,6 +1,8 @@
 package easygen
 
 import (
+	"errors"
+	"fmt"
 	"regexp"
 	"strings"
 )
@@ -10,6 +12,73 @@ var (
 	rec *regexp.Regexp
 )
 
+////////////////////////////////////////////////////////////////////////////
+// Normal String Function Definitions
+
+// Taken/adapted from hugo tpl/strings/strings.go
+
+// Substr extracts parts of a string, beginning at the character at the specified
+// position, and returns the specified number of characters.
+//
+// It normally takes two parameters: start and length.
+// It can also take one parameter: start, i.e. length is omitted, in which case
+// the substring starting from start until the end of the string will be returned.
+//
+// To extract characters from the end of the string, use a negative start number.
+//
+// In addition, borrowing from the extended behavior described at http://php.net/substr,
+// if length is given and is negative, then that many characters will be omitted from
+// the end of string.
+func Substr(a string, nums ...interface{}) (string, error) {
+	var start, length int
+
+	asRunes := []rune(a)
+
+	switch len(nums) {
+	case 0:
+		return "", errors.New("too less arguments")
+	case 1:
+		start = nums[0].(int)
+		length = len(asRunes)
+	case 2:
+		start = nums[0].(int)
+		length = nums[1].(int)
+	default:
+		return "", errors.New("too many arguments")
+	}
+
+	if start < -len(asRunes) {
+		start = 0
+	}
+	if start > len(asRunes) {
+		return "", fmt.Errorf("start position out of bounds for %d-byte string", len(a))
+	}
+
+	var s, e int
+	if start >= 0 && length >= 0 {
+		s = start
+		e = start + length
+	} else if start < 0 && length >= 0 {
+		s = len(asRunes) + start
+		e = len(asRunes) + start + length + 1
+	} else if start >= 0 && length < 0 {
+		s = start
+		e = len(asRunes) + length
+	} else {
+		s = len(asRunes) + start
+		e = len(asRunes) + length
+	}
+
+	if s > e {
+		return "", fmt.Errorf("calculated start position greater than end position: %d > %d", s, e)
+	}
+	if e > len(asRunes) {
+		e = len(asRunes)
+	}
+
+	return string(asRunes[s:e]), nil
+}
+
 ////////////////////////////////////////////////////////////////////////////
 // Regexp Function Definitions
 

using_easygen.md

@@ -11,6 +11,21 @@ I.e., with the environment variable `EASYGEN_TS`, the `.tmpl` template file is n
 
 	$ EASYGEN_TS='{{.Name}}' easygen -ts '{{clk2uc .Name}}' /tmp/var
 	SomeInitMethod
+	
+	$ easygen -ts '{{substr (clk2uc .Name) 4}}' /tmp/var
+	InitMethod
+	
+	$ easygen -ts '{{substr (clk2uc .Name) 8 3}}' /tmp/var
+	Met
+	
+	$ easygen -ts '{{substr (clk2uc .Name) 4 -2}}' /tmp/var
+	InitMeth
+
+	$ easygen -ts '{{substr (clk2uc .Name) -6}}' /tmp/var
+	Method
+
+	$ easygen -ts '{{substr "abcde" -3}}' /tmp/var
+	cde
 
 I.e., command line value takes the highest priority, even overriding the environment variable `EASYGEN_TS`'s value.