Newbie: how to handle pipes and semicolons while launching UNIX commands?

Question

Good afternoon,
I am trying to write a Java class that can launch UNIX commands.
Launching simple commands (date, ps -ef) works fine, but when I start using pipes and semicolons, it goes wrong:
Java code (pipe example):
        String command = "ps -ef | grep config";
        Process child = Runtime.getRuntime().exec(command);Result:
usage: ps [ -aAdeflcjLPy ] [ -o format ] [ -t termlist ]
        [ -u userlist ] [ -U userlist ] [ -G grouplist ]
        [ -p proclist ] [ -g pgrplist ] [ -s sidlist ]
  'format' is one or more of:
        user ruser group rgroup uid ruid gid rgid pid ppid pgid sid taskid
        pri opri pcpu pmem vsz rss osz nice class time etime stime
        f s c lwp nlwp psr tty addr wchan fname comm args projid projectJava code (semicolon example):
        String command = "date;ps -ef";
        Process child = Runtime.getRuntime().exec(command);Result:
date;ps: not foundClearly the pipes and the semicolons are handled by the UNIX shell and cannot be put in the Java source code as such.
Does anybody know a way around this?
Thanks
Dominique

Answer 1

Pipes and semicolons are interpreted by a shell (bash, csh etc) and when one executes as you are doing no shell is involved. This is easy to solve by using the alternate version of exec() which takes an array as an argument and to use your shell of choice. For example :-
String[] command = {"bash", "-c", "date;ps -ef"};Note that the third argument is the whole of the command to be interpreted.
Two points to consider. First you should read, digest and implement all the recommendations in http://www.javaworld.com/jw-12-2000/jw-1229-traps.html; failure to do so will at some point lead to significant loss of hair. Second you should probably use ProcessBuilder rather than Runtime.exec(). Behind the scenes Runtime.exec() uses ProcessBuilder but ProcessBuilder provides a better interface with more features.