Java Runtime getRuntime getting output from executing a command line program

Question

I m using the runtime to run command prompt commands from my Java program  However  I m not aware of how I can get the output the command returns   Here is my code   Runtime rt   Runtime getRuntime     String   commands     system exe    -send    argument    Process proc   rt exec commands     I tried doing System out println proc   but that did not return anything  The execution of that command should return two numbers separated by a semicolon  How could I get this in a variable to print out   Here is the code I m using now   String   commands     system exe    -get t     Process proc   rt exec commands    InputStream stdIn   proc getInputStream    InputStreamReader isr   new InputStreamReader stdIn   BufferedReader br   new BufferedReader isr    String line   null  System out println   lt OUTPUT gt      while   line   br readLine       null       System out println line    System out println   lt  OUTPUT gt     int exitVal   proc waitFor    System out println  Process exitValue      exitVal     But I m not getting anything as my output  but when I run that command myself it works fine

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Besides using ProcessBuilder as suggested Senthil  be sure to read and implement all the recommendations of When Runtime exec   won t

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If you write on Kotlin  you can use   val firstProcess   ProcessBuilder  echo   hello world   start   val firstError   firstProcess errorStream readBytes   decodeToString   val firstResult   firstProcess inputStream readBytes   decodeToString

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Adapted from the previous answer   public static String execCmdSync String cmd  CmdExecResult callback  throws java io IOException  InterruptedException       RLog i TAG   Running command    cmd        Runtime rt   Runtime getRuntime        Process proc   rt exec cmd          String   commands     system exe    -get t         BufferedReader stdInput   new BufferedReader new InputStreamReader proc getInputStream          BufferedReader stdError   new BufferedReader new InputStreamReader proc getErrorStream           StringBuffer stdOut   new StringBuffer        StringBuffer errOut   new StringBuffer            Read the output from the command      System out println  Here is the standard output of the command  n        String s   null      while   s   stdInput readLine       null            System out println s           stdOut append 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           errOut append s              if  callback    null            return stdInput toString               int exitVal   proc waitFor        callback onComplete exitVal    0  exitVal  errOut toString    stdOut toString    cmd        return stdInput toString       public interface CmdExecResult      void onComplete boolean success  int exitVal  String error  String output  String originalCmd

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If use are already have Apache commons-io available on the classpath  you may use   Process p   new ProcessBuilder  cat     etc something   start    String stderr   IOUtils toString p getErrorStream    Charset defaultCharset     String stdout   IOUtils toString p getInputStream    Charset defaultCharset

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At the time of this writing  all other answers that include code may result in deadlocks   Processes have a limited buffer for stdout and stderr output  If you don t listen to them concurrently  one of them will fill up while you are trying reading the other  For example  you could be waiting to read from stdout while the process is waiting to write to stderr  You cannot read from the stdout buffer because it is empty and the process cannot write to the stderr buffer because it is full  You are each waiting on each other forever   Here is a possible way to read the output of a process without a risk of deadlocks   public final class Processes       private static final String NEWLINE   System getProperty  line separator                     param command the command to run         return the output of the command         throws IOException if an I O error occurs             public static String run String    command  throws IOException               ProcessBuilder pb   new ProcessBuilder command  redirectErrorStream true           Process process   pb start            StringBuilder result   new StringBuilder 80           try  BufferedReader in   new BufferedReader new InputStreamReader process getInputStream                            while  true                                String line   in readLine                    if  line    null                      break                  result append line  append NEWLINE                                   return result toString                          Prevent construction              private Processes                   The key is to use ProcessBuilder redirectErrorStream true  which will redirect stderr into the stdout stream  This allows you to read a single stream without having to alternate between stdout and stderr  If you want to implement this manually  you will have to consume the streams in two different threads to make sure you never block

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Here is the way to go   Runtime rt   Runtime getRuntime    String   commands     system exe    -get t    Process proc   rt exec commands    BufferedReader stdInput   new BufferedReader new       InputStreamReader proc getInputStream       BufferedReader stdError   new BufferedReader new       InputStreamReader proc getErrorStream          Read the output from the command System out println  Here is the 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  Here is the standard error of the command  if any   n    while   s   stdError readLine       null        System out println s       Read the Javadoc for more details here  ProcessBuilder would be a good choice to use

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Process p   Runtime getRuntime   exec  quot ping google com quot     p getInputStream   transferTo System out    p getErrorStream   transferTo System out

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Senthil and  Arend answer  https   stackoverflow com a 5711150 2268559  mentioned ProcessBuilder  Here is the example using ProcessBuilder with specifying environment variables and working folder for the command       ProcessBuilder pb   new ProcessBuilder  ls    -a    -l         Map lt String  String gt  env   pb environment           If you want clean environment  call env clear   first       env clear        env put  VAR1    myValue        env remove  OTHERVAR        env put  VAR2   env get  VAR1      suffix         File workingFolder   new File   home user        pb directory workingFolder        Process proc   pb start         BufferedReader stdInput   new BufferedReader new InputStreamReader proc getInputStream           BufferedReader stdError   new BufferedReader new InputStreamReader proc getErrorStream              Read the output from the command      System out println  Here is the 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  Here is the standard error of the command  if any   n        while   s   stdError readLine       null          System out println s

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Also we can use streams for obtain command output   public static void main String   args  throws IOException            Runtime runtime   Runtime getRuntime            String   commands      free    -h            Process process   runtime exec commands            BufferedReader lineReader   new BufferedReader new InputStreamReader process getInputStream              lineReader lines   forEach System out  println            BufferedReader errorReader   new BufferedReader new InputStreamReader process getErrorStream              errorReader lines   forEach System out  println

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Pretty much the same as other snippets on this page but just organizing things up over an function  here we go     String str shell exec  ls -l      The Class function   public String shell exec String cmd                  String o null         try                     Process p Runtime getRuntime   exec cmd            BufferedReader b new BufferedReader new InputStreamReader p getInputStream               String r           while  r b readLine     null o  r            catch Exception e  o  error           return o

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A quicker way is this  public static String execCmd String cmd  throws java io IOException       java util Scanner s   new java util Scanner Runtime getRuntime   exec cmd  getInputStream    useDelimiter  quot   A quot        return s hasNext     s next      quot  quot      Which is basically a condensed version of this  public static String execCmd String cmd  throws java io IOException       Process proc   Runtime getRuntime   exec cmd       java io InputStream is   proc getInputStream        java util Scanner s   new java util Scanner is  useDelimiter  quot   A quot        String val    quot  quot       if  s hasNext              val   s next              else           val    quot  quot             return val     I know this question is old but I am posting this answer because I think this may be quicker  Edit  For Java 7 and above  Need to close Streams and Scanners  Using AutoCloseable for neat code  public static String execCmd String cmd        String result   null      try  InputStream inputStream   Runtime getRuntime   exec cmd  getInputStream                Scanner s   new Scanner inputStream  useDelimiter  quot   A quot              result   s hasNext     s next     null        catch  IOException e            e printStackTrace              return result

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Try reading the InputStream of the runtime   Runtime rt   Runtime getRuntime    String   commands     system exe    -send   argument   Process proc   rt exec commands   BufferedReader br   new BufferedReader      new InputStreamReader proc getInputStream      String line  while   line   br readLine       null      System out println line     You might also need to read the error stream  proc getErrorStream    if the process is printing error output  You can redirect the error stream to the input stream if you use ProcessBuilder

[java] Java Runtime.getRuntime(): getting output from executing a command line program

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