Here, we will see Simulation of Linux cd command in Go. We will do directory changes without OS call with program.
Simulating a “cd” Linux command that changes a current directory in a file system. The simulated command takes two path strings from the command line and prints either a new path or an error.
The first path is a current working directory and second path is a new directory. Here a directory name can only contain alphanumeric characters.
- A single dot (“.”) indicates a current directory.
- the two dots (“..”) indicate a step to a previous directory, up from the current one.
- A single forward slash “/” indicates a root directory.
- Multiple consecutive slashes (////) are treated as equivalent to one (/).
You have to print a new path.
Example:
$ go build mycd.go $ ./mycd / abc Output: /abc $ mycd /abc/def ghi Output: /abc/def/ghi $ mycd /abc/def .. Output: /abc $ mycd /abc/def /abc Output: /abc $ mycd /abc/def /abc/klm Output: /abc/klm $ mycd /abc/def ../.. Output: / $ mycd /abc/def ../../.. Output: / $ mycd /abc/def . Output: /abc/def $ mycd /abc/def ..klm Output: ..klm: No such file or directory $ mycd /abc/def ////// Output: / $ mycd /abc/def ...... Output: ......: No such file or directory $ mycd /abc/def ../gh///../klm/. Output: /abc/klm
Code to Simulation of Linux cd command in Go
package main
import (
"fmt"
"os"
"regexp"
"strings"
)
func remove_index_from_slice_of_strings(slice []string, index int) []string {
return append(slice[:index], slice[index+1:]...)
}
func panic_recovery(err error) {
if err := recover(); err != nil { //catch
fmt.Println("mycd: ", err)
os.Exit(1)
}
}
func is_alphanum(word string) bool {
return regexp.MustCompile(`^[a-zA-Z0-9]*$`).MatchString(word)
}
func remove_empty_index_in_slice(slice []string, from_index int) []string {
for i := from_index; i < len(slice); {
if strings.Compare(slice[i], "") == 0 {
slice = remove_index_from_slice_of_strings(slice, i)
} else {
break
}
}
return slice
}
func validate_and_convert_dir_path_to_slice(dir_path string) []string {
dir_path_list := strings.Split(dir_path, "/")
if strings.Compare(dir_path_list[0], "") == 0 {
dir_path_list = remove_empty_index_in_slice(dir_path_list, 1)
}
for i, dir_name := range dir_path_list {
// Validate if dir name is alphanumeric or not
if !(is_alphanum(dir_name) ||
(strings.Compare(dir_name, "..") == 0) ||
(strings.Compare(dir_name, ".") == 0)) {
panic(dir_name + ": No such file or directory")
}
// Remove extra backslashes if persists (In strings.Split with "/"
// converts backslashes to empty string)
if strings.Compare(dir_name, "") == 0 {
if i == 0 {
// ignore first backslash if exists
continue
}
dir_path_list = remove_empty_index_in_slice(dir_path_list, i)
}
}
return dir_path_list
}
func back_to_the_child_path(cwd []string) []string {
return append(cwd[:len(cwd)-1], cwd[len(cwd):]...)
}
func prepare_new_dir(cwd_dir_path_list, new_dir_path_list []string) string {
new_dir := "/"
if strings.Compare(new_dir_path_list[0], "") == 0 {
// If target path starts with "/". Checking with empty string because In strings.Split with "/"
// "/" converts backslash to empty string in slice of strings
if len(new_dir_path_list) == 1 && strings.Compare(new_dir_path_list[0], "") == 0 {
// If target has only backslash "/"
return new_dir
}
new_dir = strings.Join(new_dir_path_list, "/")
return new_dir
}
for i := 0; i < len(new_dir_path_list); i++ {
if strings.Compare(new_dir_path_list[i], "") == 0 ||
strings.Compare(new_dir_path_list[i], ".") == 0 {
continue
}
if strings.Compare(new_dir_path_list[i], "..") == 0 {
if len(cwd_dir_path_list) > 1 {
cwd_dir_path_list = back_to_the_child_path(cwd_dir_path_list)
}
} else {
cwd_dir_path_list = append(cwd_dir_path_list, new_dir_path_list[i])
}
}
if len(cwd_dir_path_list) == 1 && strings.Compare(cwd_dir_path_list[0], "") == 0 {
return new_dir
} else {
new_dir = strings.Join(cwd_dir_path_list, "/")
return new_dir
}
}
func main() {
defer panic_recovery(nil)
if len(os.Args) < 3 {
panic("too few arguments")
} else if len(os.Args) > 3 {
panic("too many arguments")
}
cwd := os.Args[1]
to_dirctory := os.Args[2]
cwd_dir_path_list := validate_and_convert_dir_path_to_slice(cwd)
new_dir_path_list := validate_and_convert_dir_path_to_slice(to_dirctory)
new_dir := prepare_new_dir(cwd_dir_path_list, new_dir_path_list)
fmt.Println(new_dir)
}
Output:
% go build mycd.go % ./mycd /abc wd/ss/../dsds/../dd/ddee/./../ Output: /abc/wd/dd
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