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How should I call a Perl Script in Java?
I have a perl file which is used for remotely checking ip addresses.I need to run that perl in java.please help me to proceed.
ProcessBuilder example
import java.io.BufferedReader;
import java.io.File;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import org.apache.commons.io.FileUtils;
OutputStreamWriter writer =null;
BufferedReader stdoutBR = null;
try {
File tmp = new File("temp_dir");
File cmdFile = File.createTempFile("foo", ".sh", tmp);
File stdout = File.createTempFile("foo_stdout", ".txt", tmp);
File stderr = File.createTempFile("foo_stderr", ".txt", tmp);
String script = "/usr/bin/perl foo.pl 2>"+stderr.getAbsolutePath()+" >"+stdout.getAbsolutePath()+" \n";
cmdFile.setExecutable(true);
FileUtils.writeStringToFile(cmdFile, script);
ProcessBuilder processBuilder = new ProcessBuilder(cmdFile.getAbsolutePath());
processBuilder.redirectErrorStream(true);
Process process = processBuilder.start();
InputStream numbStream = process.getInputStream();
stdoutBR = new BufferedReader(new InputStreamReader(numbStream));
String line = null;
StringBuilder unexpectedOutput = new StringBuilder();
while ((line = stdoutBR.readLine()) !=null) {
unexpectedOutput.append(line);
unexpectedOutput.append("\n");
}
process.waitFor();
stdoutBR.close();
log.debug("Process exit value:"+process.exitValue());
if (process.exitValue() != 0) {
String stdoutString = FileUtils.readFileToString(stdout);
String stderrString = FileUtils.readFileToString(stderr);
throw new RuntimeException("Problem executing script. \nOutput:"+unexpectedOutput.toString()+"\nStdout:"+stdoutString+"\nStderr:"+stderrString);
}
String output = FileUtils.readFileToString(stdout);
FileUtils.deleteQuietly(cmdFile);
FileUtils.deleteQuietly(stdout);
FileUtils.deleteQuietly(stderr);
} finally {
try {
if (writer != null) {
writer.close();
}
}
catch (Exception e) {
//TODO
}
}
You need the Runtime.getRuntime().exec() method. Some points to consider:
you must explicitly call perl in the command line: "perl myprog.pl". The implicit interpreter selection that the kernel normally does doesn't work in the exec() method.
you must make sure that the path to perl is in your program's PATH environment,
or in the environment that you pass to the exec() call
you must completely drain the stdout and the stderr of the Process that you created, or the call will not terminate.
(The ProcessBuilder class mentioned above simplifies some of these issues.)
Related
I am trying to call python within my java code. However I found that if I import numpy in my python code, this is my java code
Process pcs = Runtime.getRuntime().exec(cmd);
String result = null;
BufferedInputStream in = new BufferedInputStream(pcs.getInputStream());
BufferedReader br = new BufferedReader(new InputStreamReader(in));
System.out.println("\nExecuting python script file now.");
String lineStr = null;
while ((lineStr = br.readLine()) != null) {
result = lineStr;
}
br.close();
in.close();
System.out.println("done!");
System.out.println(result);
This is my python code:
import sys
import os
import numpy as np
a = sys.argv[1]
b = sys.argv[2]
print("hello world!")
print("%s * %s = %s"%(a,b,int(a)*int(b)))
Results if I don't include "import numpy as np":
10 * 11 = 110
Results if include "import numpy as np":
null
Any intuitive explanation?
import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.InputStreamReader;
public class Hello{
public static void main(String[] args)throws java.io.IOException{
Process pcs=Runtime.getRuntime().exec("python test.py 8 5");// in linux or unix use python3 or python
String result=null;
BufferedInputStream in = new BufferedInputStream(pcs.getInputStream());
BufferedReader br = new BufferedReader(new InputStreamReader(in));
System.out.println("\nExecuting python script file now.");
String lineStr = null;
while ((lineStr = br.readLine()) != null) {
result = lineStr;
}
br.close();
in.close();
System.out.println("done!");
System.out.println(result);
}
}
java code
compile:
javac Hello.java
run:
java Hello
#test.py
import sys
import os
import numpy as np
a = sys.argv[1]
b = sys.argv[2]
print("hello world!")
print("%s * %s = %s"%(a,b,int(a)*int(b)))
Have you got the right PYTHONPATH setup in your application? When you have import numpy as np in your code, you may be receiving back empty STDOUT and an ModuleNotFoundError in STDERR. You can confirm by extracting STDERR - or check with this code:
Launch.exe(cmd);
where Launch.java is:
public class Launch
{
/** Launch using FILE redirects */
public static int exec(String[] cmd) throws InterruptedException, IOException
{
System.out.println("exec "+Arrays.toString(cmd));
Path tmpdir = Path.of(System.getProperty("java.io.tmpdir"));
ProcessBuilder pb = new ProcessBuilder(cmd);
Path out = tmpdir.resolve(cmd[0]+"-stdout.log");
Path err = tmpdir.resolve(cmd[0]+"-stderr.log");
pb.redirectError(out.toFile());
pb.redirectOutput(err.toFile());
Process p = pb.start();
int rc = p.waitFor();
System.out.println("Exit "+rc +' '+(rc == 0 ? "OK":"**** ERROR ****")
+" STDOUT \""+Files.readString(out)+'"'
+" STDERR \""+Files.readString(err)+'"');
System.out.println();
return rc;
}
}
The fix for using numpy should be to access ProcessBuilder pb.environment() and set your PYTHONPATH for the subprocess before calling start()
I am trying to view the temperature table for my CPU on my Linux machine with Java. This bit of code will display the shell output for other commands, ls, cat file, but will not display watch sensors as it returns an interactive output. Is there a way I can convert it to plain text somehow?
Error: [/usr/bin/watch, sensors]
Error opening terminal: unknown.
import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
public class tempapp{
public static void main (String args[]) throws IOException, InterruptedException {
//build command
List<String> commands = new ArrayList<String>();
commands.add("/usr/bin/watch");
//args
commands.add("sensors");
System.out.println(commands);
ProcessBuilder pb = new ProcessBuilder(commands);
pb.directory(new File("/home/ethano"));
pb.redirectErrorStream(true);
Process process = pb.start();
//Read output
StringBuilder out = new StringBuilder();
BufferedReader br = new BufferedReader(new InputStreamReader(process.getInputStream()));
String line = null, previous = null;
while ((line = br.readLine()) != null)
if (!line.equals(previous)) {
previous = line;
out.append(line).append('\n');
System.out.println(line);
}
//Check result
if (process.waitFor() == 0){
System.out.println("\n success");
System.exit(0);
}
//weird termination
System.err.println(commands);
System.err.println(out.toString());
System.exit(1);
}
}
All that watch does is call the command it is given (sensors in this case) once every two seconds. You can simply have your application emulate this behaviour by calling /usr/bin/sensors in a for-loop once every two seconds (or however many times you need), therefore omitting the need to read interactive shell output.
I am trying to use the cat command from within a java program to merge two files into one. The line of code which contains the cat command takes two files file1 and file2 and writes to a third file called combinedfile. However, what I observe is the instead of creating this file (combinedfile) and writing to it, my program merely displays the output on the terminal.
How can I make sure that indeed the two files are copied to a third file.
import java.io.BufferedReader;
import java.io.InputStreamReader;
public class ExecuteShellCommand
{
public static void main(String[] args)
{
ExecuteShellCommand obj = new ExecuteShellCommand();
String command = "cat file1 file2 > combinedfile";
String output = obj.executeCommand(command);
System.out.println(output);
}
private 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();
}
}
EDIT:
I tried out with the ProcessBuilder as suggested, but I get this error.
Code
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.*;
import java.util.*;
public class ExecuteShellCommand
{
public static void main(String[] args)
{
try
{
ProcessBuilder builder = new ProcessBuilder("cat", "/home/PepperBoy/Desktop/file1.txt","/home/PepperBoy/Desktop/file2.txt");
File combinedFile = new File("/home/PepperBoy/Desktop/file3.txt");
builder.redirectOutput(combinedFile);
builder.redirectError(combinedFile);
Process p = builder.start();
}
catch(IOException e)
{
e.printStackTrace();
}
}
}
Error
ExecuteShellCommand.java:14: cannot find symbol
symbol : method redirectOutput(java.io.File)
location: class java.lang.ProcessBuilder
builder.redirectOutput(combinedFile);
I found a related question. To summarize the useful things from a couple answers found there, file redirection requires a shell, but exec doesn't have a shell context. Luckily, you can execute processes with redirection using ProcessBuilder. For your case, that would look something like:
public static void main(String[] args)
{
try{
ProcessBuilder builder = new ProcessBuilder("cat", "file1","file2");
File combinedFile = new File("combinedFile");
builder.redirectOutput(combinedFile);
builder.redirectError(combinedFile);
Process p = builder.start();
} catch(IOException e){
//handle exception...
}
}
Note: You may receive an error when calling redirectError or redirectOutput stating that the symbol cannot be found. This will occur if you are compiling against a version of Java before 1.7, since 1.7 is when these methods were introduced. If it is possible to upgrade your Java, doing so will eliminate this error.
If it is not possible to upgrade Java, the following code will work:
public static void main(String[] args)
{
try{
ProcessBuilder builder = new ProcessBuilder("cat", "file1","file2");
File combinedFile = new File("combinedFile");
Process p = builder.start();
InputStream isFromCat = p.getInputStream();
OutputStream osCombinedFile = new FileOutputStream(combinedFile);
byte[] buffer = new byte[1024];
int read = 0;
while((read = isFromCat.read(buffer)) != -1) {
osCombinedFile.write(buffer, 0, read);
}
} catch(IOException e){
//handle exception...
}
}
It is also probably worthwhile to note that making a system call to cat is not the optimal way to combine files from Java. I have been assuming this is a toy case to represent a more complex use case for you. If all you really want to do is combine two files, you should write your code to avoid system calls and just append the files by reading both in as input streams and then writing them out to the result file. If you're having trouble figuring that out, those details definitely belong in another question.
I want to execute a command which takes 2 arguments.
1.input file name
2.output file name.
The command is sixV1.1 outputFile.txt
The code is:
String cmd= "sixV1.1 <inputFile.txt >outputFile.txt";
Process p=Runtime.getRuntime().exec(cmd);
int retValue=p.waitFor();
when the i run above code,it is taking infinite time.
Is it possible to give <, > charecters in cmd .Please suggest me....
The right way to do input/output redirection when you start a process in Java is to write/read from the process's streams:
Process p = Runtime.getRuntime().exec("sixV1.1");
InputStream is = p.getInputStream();
// read from is and write to outputFile.txt
OutputStream os = p.getOutputStream();
// read from inputFile.txt and write to os
There's a fantastic blog post by Michael C. Daconta about successful command line calls using Runtime in Java. It's not as easy as you might think!
The following code extract from that blog post describes "MediocreExecJava", a class that successfully runs a program using Runtime.exec() and manages its input and output without hanging. I've used it before and it works. I highly recommend reading the post to understand why!
import java.util.*;
import java.io.*;
public class MediocreExecJavac
{
public static void main(String args[])
{
try
{
Runtime rt = Runtime.getRuntime();
Process proc = rt.exec("javac");
InputStream stderr = proc.getErrorStream();
InputStreamReader isr = new InputStreamReader(stderr);
BufferedReader br = new BufferedReader(isr);
String line = null;
System.out.println("<ERROR>");
while ( (line = br.readLine()) != null)
System.out.println(line);
System.out.println("</ERROR>");
int exitVal = proc.waitFor();
System.out.println("Process exitValue: " + exitVal);
} catch (Throwable t)
{
t.printStackTrace();
}
}
}
I am trying to execute some Linux commands from Java using redirection (>&) and pipes (|). How can Java invoke csh or bash commands?
I tried to use this:
Process p = Runtime.getRuntime().exec("shell command");
But it's not compatible with redirections or pipes.
exec does not execute a command in your shell
try
Process p = Runtime.getRuntime().exec(new String[]{"csh","-c","cat /home/narek/pk.txt"});
instead.
EDIT::
I don't have csh on my system so I used bash instead. The following worked for me
Process p = Runtime.getRuntime().exec(new String[]{"bash","-c","ls /home/XXX"});
Use ProcessBuilder to separate commands and arguments instead of spaces. This should work regardless of shell used:
import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
public class Test {
public static void main(final String[] args) throws IOException, InterruptedException {
//Build command
List<String> commands = new ArrayList<String>();
commands.add("/bin/cat");
//Add arguments
commands.add("/home/narek/pk.txt");
System.out.println(commands);
//Run macro on target
ProcessBuilder pb = new ProcessBuilder(commands);
pb.directory(new File("/home/narek"));
pb.redirectErrorStream(true);
Process process = pb.start();
//Read output
StringBuilder out = new StringBuilder();
BufferedReader br = new BufferedReader(new InputStreamReader(process.getInputStream()));
String line = null, previous = null;
while ((line = br.readLine()) != null)
if (!line.equals(previous)) {
previous = line;
out.append(line).append('\n');
System.out.println(line);
}
//Check result
if (process.waitFor() == 0) {
System.out.println("Success!");
System.exit(0);
}
//Abnormal termination: Log command parameters and output and throw ExecutionException
System.err.println(commands);
System.err.println(out.toString());
System.exit(1);
}
}
Building on #Tim's example to make a self-contained method:
import java.io.BufferedReader;
import java.io.File;
import java.io.InputStreamReader;
import java.util.ArrayList;
public class Shell {
/** Returns null if it failed for some reason.
*/
public static ArrayList<String> command(final String cmdline,
final String directory) {
try {
Process process =
new ProcessBuilder(new String[] {"bash", "-c", cmdline})
.redirectErrorStream(true)
.directory(new File(directory))
.start();
ArrayList<String> output = new ArrayList<String>();
BufferedReader br = new BufferedReader(
new InputStreamReader(process.getInputStream()));
String line = null;
while ( (line = br.readLine()) != null )
output.add(line);
//There should really be a timeout here.
if (0 != process.waitFor())
return null;
return output;
} catch (Exception e) {
//Warning: doing this is no good in high quality applications.
//Instead, present appropriate error messages to the user.
//But it's perfectly fine for prototyping.
return null;
}
}
public static void main(String[] args) {
test("which bash");
test("find . -type f -printf '%T#\\\\t%p\\\\n' "
+ "| sort -n | cut -f 2- | "
+ "sed -e 's/ /\\\\\\\\ /g' | xargs ls -halt");
}
static void test(String cmdline) {
ArrayList<String> output = command(cmdline, ".");
if (null == output)
System.out.println("\n\n\t\tCOMMAND FAILED: " + cmdline);
else
for (String line : output)
System.out.println(line);
}
}
(The test example is a command that lists all files in a directory and its subdirectories, recursively, in chronological order.)
By the way, if somebody can tell me why I need four and eight backslashes there, instead of two and four, I can learn something. There is one more level of unescaping happening than what I am counting.
Edit: Just tried this same code on Linux, and there it turns out that I need half as many backslashes in the test command! (That is: the expected number of two and four.) Now it's no longer just weird, it's a portability problem.