Example of Unix commands implemented in Java

I created some illustrative and simple implementations of common Unix commands. For those who are familiar with Unix-like systems them make easier to understand Java. For those who are familiar with Java them make easier to understand Unix-like systems. :-)

1. PWD

The first one is pwd that show the current working directory.

public class Jpwd {
public static void main(String[] args) {
String pwd = System.getProperty("user.dir");
System.out.println(pwd);
}
}

Running this at /home/silveira directory gives us as output:

$ java Jpwd
/home/silveira

1. CAT

The command cat is usually utilized for displaying files.

import java.io.BufferedReader; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.IOException; public class Jcat { public static void main(String[] args) { if(args.length==1){ try { FileReader fileReader = new FileReader(args[0]); BufferedReader in = new BufferedReader(fileReader); String line; while((line = in.readLine())!= null){ System.out.println(line); } } catch (FileNotFoundException ex) { System.out.println(args[0]+", file not found."); } catch (IOException ex) { System.out.println(args[0]+", input/output error."); } } } }

$ java Jcat /etc/timezone
America/Fortaleza

3. LS

The command ls is to list files. The File API (java.io.File) is very flexible and portable, but in this
example I want just list files and directories of the current directory.

import java.io.File;

public class Jls {
public static void main(String[] args) {
File dir = new File(System.getProperty("user.dir"));
String childs[] = dir.list();
for(String child: childs){
System.out.println(child);
}
}
}

Usage:

$ java Jpwd
/home/silveira/example
$ java Jls
directoryA
fileA
.somefile

4. CD

The cd command changes the current working directory.

import java.io.File; public class Jcd { public static void main(String[] args) { if(args.length==1){ File dir = new File(args[0]); if(dir.isDirectory()==true) { System.setProperty("user.dir", dir.getAbsolutePath()); } else { System.out.println(args[0] + "is not a directory."); } } } }

Usage:

$ java Jpwd

/home/silveira

$ java Jcd /tmp

$ java Jpwd

/tmp