Merge branch 'feature/path-search' into feature/cat

free/main.go

@@ -95,7 +95,7 @@ func main() {
 	flag.Parse()
 
 	if !*jsonModePtr {
-		fmt.Printf("%s", jsh.Fallback("/usr/bin/free"))
+		fmt.Printf("%s", jsh.Fallback("free"))
 	} else {
 		runJsonMode()
 	}

ps/main.go

@@ -25,7 +25,7 @@ func PsOutputToProcesses(out string) *[]jsh.Process {
 
 func runJsonMode() {
 	// Run procps-ng "ps" with full output
-	psOut := string(*jsh.FallbackWithArgs("/usr/bin/ps", []string{"auxww"}))
+	psOut := string(*jsh.FallbackWithArgs("ps", []string{"auxww"}))
 	processesPtr := PsOutputToProcesses(psOut)
 	frame := jsh.JshFrame{*processesPtr, []string{}}
 
@@ -43,7 +43,7 @@ func main() {
 	flag.Parse()
 
 	if !*jsonModePtr {
-		fmt.Printf("%s", jsh.Fallback("/usr/bin/ps"))
+		fmt.Printf("%s", jsh.Fallback("ps"))
 	} else {
 		runJsonMode()
 	}

utils.go

@@ -1,9 +1,12 @@
 package jsh
 
 import (
+	"errors"
+	"fmt"
 	"math"
 	"os"
 	"os/exec"
+	"strings"
 	"unicode"
 )
 
@@ -52,7 +55,13 @@ func FallbackWithArgs(program string, args []string) *[]byte {
 	if args == nil {
 		args = os.Args[1:]
 	}
-	out, err := exec.Command(program, args...).Output()
+	executable, err := findExecutable(program)
+
+	if err != nil {
+		panic(err)
+	}
+
+	out, err := exec.Command(executable, args...).Output()
 	if err != nil {
 		panic(err)
 	}
@@ -62,3 +71,58 @@ func FallbackWithArgs(program string, args []string) *[]byte {
 func Fallback(program string) *[]byte {
 	return FallbackWithArgs(program, nil)
 }
+
+// Finds a given executable on the system path, returning the absolute path the program if found, and an error
+// if it's not found
+func findExecutable(programName string) (string, error) {
+	// First, find our binary location
+	binLocWithName, err := os.Readlink("/proc/self/exe")
+	if err != nil {
+		return "", err
+	}
+	// Get our binary name and remove it from the binary path, leaving just our binary location
+	// Also trim the extra path separator
+	binName := os.Args[0]
+	binLoc := strings.TrimSuffix(binLocWithName, binName)
+	binLoc = strings.TrimSuffix(binLoc, string(os.PathSeparator))
+
+	// Get the system path and split it by the system path separator
+	pathString := os.Getenv("PATH")
+	path := strings.Split(pathString, string(os.PathListSeparator))
+
+	// Loop until we find our location on the path, so we know where to start looking after for the
+	// next implementation of the given program name
+	var foundPath bool
+	var pathNum int
+	for index, pathEl := range path {
+		// Trim the path separator from this element, if it has it
+		pathEl = strings.TrimSuffix(pathEl, string(os.PathSeparator))
+		if pathEl == binLoc {
+			foundPath = true
+			pathNum = index
+			break
+		}
+	}
+
+	// If we found our path on the real path, then search the remaining path elements. Otherwise, search all elements
+	if foundPath {
+		return searchPath(programName, path[pathNum+1:len(path)-1])
+	} else {
+		return searchPath(programName, path)
+	}
+}
+
+// Searches the given set of paths for a the given program, returing when it finds it or returning an error if the
+// program is not found
+func searchPath(programName string, path []string) (string, error) {
+	// Loop through each path element, test for the existance of the file, and then return if we find it
+	for _, pathEl := range path {
+		fullProgram := pathEl + string(os.PathSeparator) + programName
+		_, err := os.Stat(fullProgram)
+		if err == nil {
+			return fullProgram, nil
+		}
+	}
+
+	return "", errors.New(fmt.Sprintf("Could not find program %s on the PATH: %s", programName, path))
+}