Fix #117

README.md

@@ -249,6 +249,8 @@ Get a released version on: https://github.com/moul/advanced-ssh-config/releases
 
 ### master (unreleased)
 
+* Fix: Allow `$(...)` syntax in the `ResolveCommand` function ([#117](https://github.com/moul/advanced-ssh-config/issues/117))
+* Printing the error of a failing `ResolveCommand` ([#117](https://github.com/moul/advanced-ssh-config/issues/117))
 * Fix: `Gateways` field is no longer ignored when the `HostName` field is present ([#102](https://github.com/moul/advanced-ssh-config/issues/102))
 * Ignore SIGHUP, close goroutines and export written bytes ([#112](https://github.com/moul/advanced-ssh-config/pull/112)) ([@QuentinPerez](https://github.com/QuentinPerez))
 * Various documentation improvements ([@ashmatadeen](https://github.com/ashmatadeen), [@loliee](https://github.com/loliee), [@cerisier](https://github.com/cerisier))

pkg/commands/proxy.go

@@ -1,6 +1,7 @@
 package commands
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 	"net"
@@ -178,12 +179,17 @@ func hostPrepare(host *config.Host) error {
 			return err
 		}
 
-		out, err := exec.Command(args[0], args[1:]...).Output()
-		if err != nil {
+		cmd := exec.Command(args[0], args[1:]...)
+		var stdout bytes.Buffer
+		var stderr bytes.Buffer
+		cmd.Stdout = &stdout
+		cmd.Stderr = &stderr
+		if err := cmd.Run(); err != nil {
+			Logger.Errorf("ResolveCommand failed: %s", stderr.String())
 			return err
 		}
 
-		host.HostName = strings.TrimSpace(fmt.Sprintf("%s", out))
+		host.HostName = strings.TrimSpace(fmt.Sprintf("%s", stdout.String()))
 		Logger.Debugf("Resolved host is: %s", host.HostName)
 	}
 	return nil

pkg/config/imported.go

@@ -0,0 +1,51 @@
+// This file contains imported functions
+// The license and copyright is reported for each functions in the comments.
+
+package config
+
+// Imported and unmodified from https://golang.org/src/os/env.go
+// Function under the BSD-License - Copyrighted by the Go Authors
+// isShellSpecialVar reports whether the character identifies a special
+// shell variable such as $*.
+func isShellSpecialVar(c uint8) bool {
+	switch c {
+	case '*', '#', '$', '@', '!', '?', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+		return true
+	}
+	return false
+}
+
+// Imported and unmodified from https://golang.org/src/os/env.go
+// Function under the BSD-License - Copyrighted by the Go Authors
+// isAlphaNum reports whether the byte is an ASCII letter, number, or underscore
+func isAlphaNum(c uint8) bool {
+	return c == '_' || '0' <= c && c <= '9' || 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
+}
+
+// Imported and unmodified from https://golang.org/src/os/env.go
+// Function under the BSD-License - Copyrighted by the Go Authors
+// getShellName returns the name that begins the string and the number of bytes
+// consumed to extract it.  If the name is enclosed in {}, it's part of a ${}
+// expansion and two more bytes are needed than the length of the name.
+func getShellName(s string) (string, int) {
+	switch {
+	case s[0] == '{':
+		if len(s) > 2 && isShellSpecialVar(s[1]) && s[2] == '}' {
+			return s[1:2], 3
+		}
+		// Scan to closing brace
+		for i := 1; i < len(s); i++ {
+			if s[i] == '}' {
+				return s[1:i], i + 1
+			}
+		}
+		return "", 1 // Bad syntax; just eat the brace.
+	case isShellSpecialVar(s[0]):
+		return s[0:1], 1
+	}
+	// Scan alphanumerics.
+	var i int
+	for i = 0; i < len(s) && isAlphaNum(s[i]); i++ {
+	}
+	return s[:i], i
+}

pkg/config/utils.go

@@ -17,9 +17,29 @@ func GetHomeDir() string {
 	return ""
 }
 
+// ExpandEnvSafe replaces ${var} or $var in the string according to the values
+// of the current environment variables.
+// As opposed to os.ExpandEnv, ExpandEnvSafe won't remove the dollar in '$(...)'
+// See https://golang.org/src/os/env.go?s=963:994#L22 for the original function
+func ExpandEnvSafe(s string) string {
+	buf := make([]byte, 0, 2*len(s))
+	i := 0
+	for j := 0; j < len(s); j++ {
+		// the following line is the only one changing
+		if s[j] == '$' && j+1 < len(s) && s[j+1] != '(' {
+			buf = append(buf, s[i:j]...)
+			name, w := getShellName(s[j+1:])
+			buf = append(buf, os.Getenv(name)...)
+			j += w
+			i = j + 1
+		}
+	}
+	return string(buf) + s[i:]
+}
+
 func expandUser(path string) (string, error) {
 	// Expand variables
-	path = os.ExpandEnv(path)
+	path = ExpandEnvSafe(path)
 
 	if path[:2] == "~/" {
 		homeDir := GetHomeDir()
@@ -37,5 +57,5 @@ func expandField(input string) string {
 	if input == "" {
 		return ""
 	}
-	return os.ExpandEnv(input)
+	return ExpandEnvSafe(input)
 }