I am trying to use Runtime class to execute some UNIX commands but I am getting issues if I try to use cd command.
Here is my Java program:
import java.io.*;
public class JavaRunCommand {
public static void main(String args[]) {
String s = null;
try {
Process p = Runtime.getRuntime().exec("cd;cat test.txt|grep Hello");
BufferedReader stdInput = new BufferedReader(new
InputStreamReader(p.getInputStream()));
BufferedReader stdError = new BufferedReader(new
InputStreamReader(p.getErrorStream()));
// read the output from the command
System.out.println("Here is the standard output of the command:\n");
while ((s = stdInput.readLine()) != null) {
System.out.println(s);
}
// read any errors from the attempted command
System.out.println("Here is the standard error of the command (if any):\n");
while ((s = stdError.readLine()) != null) {
System.out.println(s);
}
System.exit(0);
}
catch (IOException e) {
System.out.println("exception..");
e.printStackTrace();
System.exit(-1);
}
}
}
If I execute this then I am getting an exception as:
java.io.IOException: Cannot run program "cd": error=2, No such file or directory
at java.lang.ProcessBuilder.start(ProcessBuilder.java:1041)
at java.lang.Runtime.exec(Runtime.java:617)
at java.lang.Runtime.exec(Runtime.java:450)
at java.lang.Runtime.exec(Runtime.java:347)
at JavaRunCommand.main(JavaRunCommand.java:11)
Caused by: java.io.IOException: error=2, No such file or directory
at java.lang.UNIXProcess.forkAndExec(Native Method)
at java.lang.UNIXProcess.<init>(UNIXProcess.java:135)
at java.lang.ProcessImpl.start(ProcessImpl.java:130)
at java.lang.ProcessBuilder.start(ProcessBuilder.java:1022)
... 4 more
Please let me know how can we run multiple commands if I want to use it in Java.
If you replace
Process p = Runtime.getRuntime().exec("cd;cat test.txt|grep Hello");
with
Process p = Runtime.getRuntime().exec(new String[] { "/bin/sh", "-c", "cd && cat test.txt | grep Hello" });
it should do.
As cd is a built-in shell command you need to call your shell to execute it. When using windows you would require to call "cmd /c".
cd is a built-in shell command for traversing directories. It's therefore not an actual unix command that can be run in the way you're trying.
The easiest solution is to use absolute paths in the commands you are calling. E.g., instead of trying to run "cd /my/dir; cat test.txt" simply call "cat /my/dir/test.txt".
As you asked how to run multiple commands and gave cd;cat test.txt|grep Hello as an example, you need sh to process your command, because it is not a single executable program.
Despite of security implications (*), you can do
Process p = Runtime.getRuntime().exec("/bin/sh -c 'cd;cat test.txt|grep Hello'");
(*) It is generally considered as a bad security practice as unwanted commands can be executed depending on environment
Related
I am new to both Java and Linux, I was trying to use some Runtime.exec() commands that would allow my program to execute commands in Linux such as "cd /mnt/" and "ls --group-directories-first" to list files and directories contained in /mnt/ but I think I am making a problem with the execution.
I tried my code to only include the "ls --group-directories-first" and it worked like a charm, only problem was, it only listed subdirectories and files in the projects folder. I wanted to make my program go to /mnt/ first so I made my command line to a command array by using exec(String[] cmdarray) format as process1 = Runtime.getRuntime().exec(new String[]{"cd /mnt/","ls --group-directories-first"}); and when I ran it on linux, it just got executed without any printed runtime errors but also without any feedback/printed lines.
Here is my code:
import java.io.BufferedReader;
import java.io.InputStreamReader;
public class linCom {
public static void main(String args[]) {
String s;
Process p;
try {
p = Runtime.getRuntime().exec("ls --group-directories-first");
BufferedReader br = new BufferedReader(
new InputStreamReader(p.getInputStream()));
while ((s = br.readLine()) != null)
System.out.println("line: " + s);
p.waitFor();
System.out.println ("exit: " + p.exitValue());
p.destroy();
} catch (Exception e) {}
}
}
This worked and printed out:
"line: DummyFolder1
line: linCom.class
line: linCom.java
exit: 0"
import java.io.BufferedReader;
import java.io.InputStreamReader;
public class linCom {
public static void main(String args[]) {
String s;
Process p;
try {
p = Runtime.getRuntime().exec(new String[]{"cd /mnt/","ls --group-directories-first"});
BufferedReader br = new BufferedReader(
new InputStreamReader(p.getInputStream()));
while ((s = br.readLine()) != null)
System.out.println("line: " + s);
p.waitFor();
System.out.println ("exit: " + p.exitValue());
p.destroy();
} catch (Exception e) {}
}
}
This just got executed with no printed lines.
I expected my program to just go to the /mnt/ directory and print out subdirectories and files on there, but it just got executed with no visible runtime errors and no printed lines.
I have looked at other entries but could not find any answer to my problem.
EDIT: I changed "no errors" with "no error messages" to make it clear that if program had any errors, I did not get any feedback about it.
Here's where the UNIX process model can be confusing.
What you have tries to run the program named cd /mnt/ with the first parameter of ls --group-directories-first . Unix programs can be named anything (they're just filenames) but there's no program named cd /mnt. And anyway, the cd operation is actually performed by a shell, not as a forked/execed program.
You hope to run this shell command from your Java program: cd /mnt/; ls --group-directories-first . The trouble is, Java's .exec() method does not give you a shell, so shell commands don't work.
You can try this instead. It's like running the shell command
/bin/sh -c "cd /mnt/; ls --group-directories-first"
With this, you start a shell, then tell it to run -cthe command you want.
Process p = Runtime.getRuntime().exec(new String[]{"/bin/sh",
"-c",
"cd /mnt/; ls --group-directories-first"});
But it's quite dependent on the machine where your Java program runs, so be careful.
Reference: How to invoke a Linux shell command from Java
Do not use an external process just to list files. Java has plenty of ways to do that. All of them are in the Files class. For example:
Path dir = Paths.get("/mnt");
try (Stream<Path> files = Files.list(dir).sorted(
Comparator.comparing((Path p) -> !Files.isDirectory(p))
.thenComparing(Comparator.naturalOrder()))) {
files.forEach(System.out::println);
}
Do you really need to use Runtime.exec()comands? That would make your code platafform dependent.
You could use File.listFiles():
File folder = new File("/mnt");
for (File f : folder.listFiles()) {
System.out.println(f.getName());
}
That would make the code less plataform dependent
I'm using curl for certificate-based/x509 authentication
`
String command = "curl --cert " +certificateFilePath+" --key "+ certificateKeyFilePath+" --insecure "+authUrl;
ProcessBuilder process = new ProcessBuilder(command);
Process p;
try
{
p = process.start();
BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
StringBuilder builder = new StringBuilder();
String line = null;
while ( (line = reader.readLine()) != null) {
builder.append(line);
builder.append(System.getProperty("line.separator"));
}
String result = builder.toString();
System.out.print("result ------------------: "+result);
}catch(Exception e){
e.printStackTrace();
}
`
but getting exception `
Caused by: java.io.IOException: error=2, No such file or directory
at java.lang.UNIXProcess.forkAndExec(Native Method)
at java.lang.UNIXProcess.<init>(UNIXProcess.java:247)
at java.lang.ProcessImpl.start(ProcessImpl.java:134)
at java.lang.ProcessBuilder.start(ProcessBuilder.java:1029)
`
given that the application and auth service are running inside docker-container on Ubuntu and works fine when I manually go inside the application docker-container and execute the above curl command.
Please help
From process builder docs:
https://docs.oracle.com/javase/7/docs/api/java/lang/ProcessBuilder.html
The proper way to do it is to call it with the parameters passed as separate strings otherwise it won't work. Also in order to run system commands like curl in linux or dir in windows you need to call the command interpreter - sh for linux. So your command should become something like:
ProcessBuilder process = new ProcessBuilder("sh", "-c","curl","--cert", certificationPath......);
Or you can try:
Runtime.getRuntime().exec(command); //Here you pass the whole command as a string
Could you try to run a JVM under root or with sudo java....
It may not have enough permissions for JVM.
I am getting an exception like java.io.IOException: Cannot run program cat /home/talha/* | grep -c TEXT_TO_SEARCH": error=2, No such file or directory while executing the command below despite that there are no issues when I execute the same command through the terminal. I need to execute and return the output of the command below:
cat /home/talha/* | grep -c TEXT_TO_SEARCH
Here is the method used to execute commands using Runtime class:
public static String executeCommand(String command) {
StringBuffer output = new StringBuffer();
Process p;
try {
p = Runtime.getRuntime().exec(command);
p.waitFor();
BufferedReader reader = new BufferedReader(new InputStreamReader(p.getInputStream()));
String line = "";
while ((line = reader.readLine()) != null) {
output.append(line + "\n");
}
} catch (Exception e) {
e.printStackTrace();
}
return output.toString();
}
Runtime.exec does not use a shell (like, say, /bin/bash); it passes the command directly to the operating system. This means wildcards like * and pipes (|) will not be understood, since cat (like all Unix commands) does not do any parsing of those characters. You need to use something like
p = new ProcessBuilder("bash", "-c", command).start();
or, if for some bizarre reason you need to stick to using the obsolete Runtime.exec methods:
p = Runtime.getRuntime().exec(new String[] { "bash", "-c", command });
If you are only running that cat/grep command, you should consider abandoning the use of an external process, since Java code can easily traverse a directory, read lines from each file, and match them against a regular expression:
Pattern pattern = Pattern.compile("TEXT_TO_SEARCH");
Charset charset = Charset.defaultCharset();
long count = 0;
try (DirectoryStream<Path> dir =
Files.newDirectoryStream(Paths.get("/home/talha"))) {
for (Path file : dir) {
count += Files.lines(file, charset).filter(pattern.asPredicate()).count();
}
}
Update: To recursively read all files in a tree, use Files.walk:
try (Stream<Path> tree =
Files.walk(Paths.get("/home/talha")).filter(Files::isReadable)) {
Iterator<Path> i = tree.iterator();
while (i.hasNext()) {
Path file = i.next();
try (Stream<String> lines = Files.lines(file, charset)) {
count += lines.filter(pattern.asPredicate()).count();
}
};
}
$PATH is an environment variable that tells the system where to search for executable programs (it's a list of directories separated by colons). It is usually set in your .bashrc or .cshrc file but this is only loaded when you log in. When Java runs, $PATH is likely not set because the rc file is not executed automatically, so the system can't find programs without specifying exactly where they are. Try using /bin/cat or /usr/bin/cat instead of just cat and see if it works. If it does, $PATH is your problem. You can add $PATH=/bin:/usr/bin to your script or just leave it with the directory name specified (e.g. /bin/cat).
Just because you can execute it in a login session doesn't mean it will work the same when a daemon like your Java program runs. You have to know what's in your .bashrc or .cshrc file and even sometimes how the system file is written (/etc/bashrc) in order to know how to write a script that runs under a daemon. Another consideration is that daemons often run under the context of a different user, and that throws things off, too.
I want to execute a Java CLI-program from within another Java program and get the output of the CLI-program. I've tried two different implementations (using runtime.exec() and ProcessBuilder) and they don't quite work.
Here's the peculiar part; the implementations work (catch the output) for when executing commands such as pwd but for some reason they do not catch the output of a Hello World java program executed with java Hello.
Execution code:
public static void executeCommand(String command)
{
System.out.println("Command: \"" + command + "\"");
Runtime runtime = Runtime.getRuntime();
try
{
Process process = runtime.exec(command);
BufferedReader stdInput = new BufferedReader(new
InputStreamReader(process.getInputStream()));
BufferedReader stdError = new BufferedReader(new
InputStreamReader(process.getErrorStream()));
// read the output from the command
System.out.println("Standard output of the command:\n");
String s = null;
while ((s = stdInput.readLine()) != null) {
System.out.println(s);
}
// read any errors from the attempted command
System.out.println("Standard error of the command (if any):\n");
while ((s = stdError.readLine()) != null) {
System.out.println(s);
}
} catch (Exception e)
{
e.printStackTrace();
}
}
Example output
Command: "cd /Users/axelkennedal/Desktop && java Hello"
Standard output of the command:
Standard error of the command (if any):
Command: "pwd"
Standard output of the command:
/Users/axelkennedal/Dropbox/Programmering/Java/JavaFX/Kode
Standard error of the command (if any):
I have verified that Hello does indeed print "Hello world" to the CLI when running Hello directly from the CLI instead of via executeCommand().
Hello world
public class Hello
{
public static void main(String[] args)
{
System.out.println("Hello world!");
}
}
This "cd /Users/axelkennedal/Desktop && java Hello" is not one command but two commands separated by the &&. In general it means do the first command and if the first command succeeds do the second command. You can't pass this as a single command but you can implement the logic yourself:
eg to execute "cmd1 && cmd2"
if (Runtime.getRuntime().exec("cmd1").waitFor() == 0) {
Runtime.getRuntime().exec("cmd2").waitFor();
}
However, because in this case cmd1 is to change directories there is a better way, which is to use the directory function of ProcessBuilder instead of the first command.
Process p = new ProcessBuilder("java","hello")
.directory(new File("/Users/axelkennedal/Desktop"))
.start();
Iam developing an OSGI equinox launcher which should start the OSGI framework and equinox console.I have added the five jars in a folder called as plugin as a part of the classpath/buildpath but still iam unable to execute.
Below is the command which executes successfully on the linux console and opens the osgi> prompt on linux console.
java-Dosgi.bundles=org.eclipse.equinox.console_1.1.0.v20140131-1639.jar.#start,org.apache.felix.gogo.command_0.10.0.v201209301215.jar#start,org.apache.felix.gogo.runtime_0.10.0.v201209301036.jar#start,org.apache.felix.gogo.shell_0.10.0.v201212101605.jar#start -jar org.eclipse.osgi_3.10.0.v20140606-1445.jar -console
But the above fails in my code which is as below
public static void main(String[] args) {
String command ="java-Dosgi.bundles=plugin/org.eclipse.equinox.console_1.1.0.v20140131-1639.jar#start,plugin/org.apache.felix.gogo.command_0.10.0.v201209301215.jar#start,plugin/org.apache.felix.gogo.runtime_0.10.0.v201209301036.jar#start,plugin/org.apache.felix.gogo.shell_0.10.0.v201212101605.jar#start -jar plugin/org.eclipse.osgi_3.10.1.v20140909-1633.jar -console";
try {
// using the Runtime exec method:
Process p = Runtime.getRuntime().exec(command);
BufferedReader stdInput = new BufferedReader(new
InputStreamReader(p.getInputStream()));
BufferedReader stdError = new BufferedReader(new
InputStreamReader(p.getErrorStream()));
// read the output from the command
System.out.println("Here is the standard output of the command:\n");
while ((s = stdInput.readLine()) != null) {
System.out.println(s);
}
// read any errors from the attempted command
System.out.println("Here is the standard error of the command (if any):\n");
while ((s = stdError.readLine()) != null) {
System.out.println(s);
}
System.exit(0);
}
catch (IOException e) {
System.out.println("exception happened - here's what I know: ");
e.printStackTrace();
System.exit(-1);
}
}
The error is as below
Here is the standard output of the command:
Here is the standard error of the command (if any):
Error: Unable to access jarfile plugin/org.eclipse.osgi_3.10.1.v20140909-1633.jar
The two commands (the one that is executing successfully on the Linux console and the one that fails in your code) are slightly different. In the first one you use
-jar org.eclipse.osgi_3.10.0.v20140606-1445.jar
while in the second
-jar plugin/org.eclipse.osgi_3.10.1.v20140909-1633.jar
Since the error message you get says that it cannot access plugin/org.eclipse.osgi_3.10.1.v20140909-1633.jar I assume that this jar file does not exist which is why your command is failing.