Fix handling of single-character FS

Per POSIX spec (and the various implementations), a 1-char FS should be
handled specially as a straight string split and not a regex. However,
I had overlooked this, and was only doing this in the case of "\\".
This fixes things like FS="|" as reported by @shah in #29 (thanks!).

Bumped up minor version, seems like a fairly significant change rather
than just a patch fix.

Fixes #29.

Author: benhoyt

goawk.go

@@ -43,7 +43,7 @@ import (
 )
 
 const (
-	version    = "v1.5.1"
+	version    = "v1.6.0"
 	copyright  = "GoAWK " + version + " - Copyright (c) 2019 Ben Hoyt"
 	shortUsage = "usage: goawk [-F fs] [-v var=value] [-f progfile | 'prog'] [file ...]"
 	longUsage  = `Standard AWK arguments:

interp/interp.go

@@ -21,6 +21,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"unicode/utf8"
 
 	. "github.com/benhoyt/goawk/internal/ast"
 	. "github.com/benhoyt/goawk/lexer"
@@ -1015,15 +1016,10 @@ func (p *interp) setVar(scope VarScope, index int, v value) error {
 			p.filename = p.toString(v)
 		case V_FS:
 			p.fieldSep = p.toString(v)
-			if p.fieldSep != " " {
-				fieldSep := p.fieldSep
-				if fieldSep == `\` {
-					// Other AWKs treat just `\` as regex `\\`
-					fieldSep = `\\`
-				}
-				re, err := regexp.Compile(fieldSep)
+			if utf8.RuneCountInString(p.fieldSep) > 1 {
+				re, err := regexp.Compile(p.fieldSep)
 				if err != nil {
-					return newError("invalid regex %q: %s", fieldSep, err)
+					return newError("invalid regex %q: %s", p.fieldSep, err)
 				}
 				p.fieldSepRegex = re
 			}

interp/io.go

@@ -12,6 +12,7 @@ import (
 	"os/exec"
 	"strconv"
 	"strings"
+	"unicode/utf8"
 
 	. "github.com/benhoyt/goawk/internal/ast"
 	. "github.com/benhoyt/goawk/lexer"
@@ -290,27 +291,31 @@ func (p *interp) ensureFields() {
 	if p.fieldSep == " " {
 		// FS space (default) means split fields on any whitespace
 		p.fields = strings.Fields(p.line)
+	} else if utf8.RuneCountInString(p.fieldSep) <= 1 {
+		// 1-char FS is handled as plain split (not regex)
+		p.fields = strings.Split(p.line, p.fieldSep)
 	} else if p.line == "" {
 		p.fields = nil
 	} else {
 		// Split on FS as a regex
 		p.fields = p.fieldSepRegex.Split(p.line, -1)
+	}
 
-		// Special case for when RS=="" and FS is single character,
-		// split on newline in addition to FS. See more here:
-		// https://www.gnu.org/software/gawk/manual/html_node/Multiple-Line.html
-		if p.recordSep == "" && len(p.fieldSep) == 1 {
-			fields := make([]string, 0, len(p.fields))
-			for _, field := range p.fields {
-				lines := strings.Split(field, "\n")
-				for _, line := range lines {
-					trimmed := strings.TrimSuffix(line, "\r")
-					fields = append(fields, trimmed)
-				}
+	// Special case for when RS=="" and FS is single character,
+	// split on newline in addition to FS. See more here:
+	// https://www.gnu.org/software/gawk/manual/html_node/Multiple-Line.html
+	if p.recordSep == "" && utf8.RuneCountInString(p.fieldSep) == 1 {
+		fields := make([]string, 0, len(p.fields))
+		for _, field := range p.fields {
+			lines := strings.Split(field, "\n")
+			for _, line := range lines {
+				trimmed := strings.TrimSuffix(line, "\r")
+				fields = append(fields, trimmed)
 			}
-			p.fields = fields
 		}
+		p.fields = fields
 	}
+
 	p.numFields = len(p.fields)
 }