6

I am executing the shell script using below method in java 

public static void main(String ar[])
{
  //key value are being read from properties file, here I am assigning the sample values      directly

   key=mine
   value="ls-1|tail-1"


  String[] cmd = { "jj.sh" , key,value};
  Process script_exec = Runtime.getRuntime().exec(cmd);
  script_exec.waitFor();
  if(script_exec.exitValue() != 0){
   System.out.println("Error while executing script");

  BufferedReader stdInput = new BufferedReader(new
                InputStreamReader(script_exec.getInputStream()));

  while ((s = stdInput.readLine()) != null) {
                System.out.println(s);
            }
}

The jj.sh file contains below value

#!/bin/sh

key=$1
value=`$2` 
echo $value

When I execute jj.sh using key and value directly, it give me the correct value, that is, the name of file. However with java it is giving me the result as ls -1 result (Means java is ignoring the command after '|'). When I pass the key values delimited with tilde sign ` then it simply displays the full key value i.e. ls -1|tail -1

How to execute the full command using java

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8
  • 1
    How do you run jj.sh when you do it directly? Commented Jan 9, 2015 at 20:25
  • You might have to use the full path to the shell you expect this script to run in as the first argument; the hash-bang may not make sense to the exec shell that Java spawns. Also, you are going to have to pay close attention to how some characters are escaped, as this stuff is parsed more than one time. Commented Jan 9, 2015 at 20:46
  • The question Running shell script from java code and pass arguments may be helpful to you. In particular, switch from runtime.exec() to process.start(). Also, neither is a shell; you should invoke the shell and pass the script as an argument to it. Commented Jan 9, 2015 at 20:48
  • First, your Java code doesn't actually compile. You didn't close the if block. The variables I'd allow are all strings. But then, you wrote ls-1|tail-1 without spaces and that will never fly. But then, your shell script wouldn't actually work with a pipe. You're probably running it as jj.sh key ls -1| tail -1, which actually runs jj.sh key ls -1 then passes the output to tail -1. Commented Jan 9, 2015 at 21:40
  • 1
    @Jagdeep When I run that command with your script, I get "ls: invalid option -- '|' Try `ls --help' for more information.". What do you get when you copy-paste your command? Make sure to actually copy-paste the command into a terminal, and don't run something you think is equivalent. Commented Jan 10, 2015 at 5:50

2 Answers 2

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14

The primary reason why this doesn't work is that `$2` is not the same as `ls -1 | tail -1`, even when $2 is set to that string.

If your script accepts a literal string with a command to execute, you can use eval to do so.

I created a complete example. Please copy-paste it and verify that it works before you try applying any of it to your own code. Here's Test.java:

import java.io.*;

public class Test {
  public static void main(String[] args) throws Exception {
    String[] command = { "./myscript", "key", "ls -t | tail -n 1" };
    Process process = Runtime.getRuntime().exec(command);
    BufferedReader reader = new BufferedReader(new InputStreamReader(
        process.getInputStream()));
    String s;
    while ((s = reader.readLine()) != null) {
      System.out.println("Script output: " + s);
    }
  }
}

And myscript:

#!/bin/bash
key="$1"
value=$(eval "$2")
echo "The command  $2  evaluated to: $value"

Here's how we can run myscript separately:

$ ls -t | tail -n 1
Templates

$ ./myscript foo 'ls -t | tail -n 1'
The command  ls -t | tail -n 1  evaluated to: Templates

And here's the result of running the Java code:

$ javac Test.java && java Test
Script output: The command  ls -t | tail -n 1  evaluated to: Templates
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Comments

0

As other posters pointed out already, the sub-process is not started in a shell, so the she-bang is not interpreted.

I got your example to work by explicitly starting the evaluation of the second parameter in a shell in jj.sh:

value=`sh -c "$2"`

Not nice, but works.

Other option may be to start the script in a shell explicitly, emulating the sh-bang:

String[] cmd = { "/bin/sh", "jj.sh" , key,value};
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1 Comment

It actually does run the she-bang. Try writing a shell script that only has a she-bang and a ps $$ and running it through the (corrected form of the) above program.

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