How to invoke a Linux shell command from Java

Question

I am trying to execute some Linux commands from Java using redirection    amp   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

User · Accepted Answer

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"});

User · Answer

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 lt String gt  commands   new ArrayList lt String gt             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

User · Answer

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 lt String gt  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 lt String gt  output   new ArrayList lt String gt                 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 lt String gt  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

[java] How to invoke a Linux shell command from Java

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