Executing system commands like cd on Linux from Java Code

Question

Hi,
I need to execute a few system commands (like cd, ls, tar, etc.,) on RedHat Linux 7.1 from Java code. Any ideas plz.
best wishes,
Issac

Answer 1

Since this thread mentioned using the DOS START command
from an exec(), I was wondering whether anyone else is
seeing the odd behavior I am.
Most of the examples showing how to read stdout and stderr
while the process is running show simple loops that use
getInputStream and getErrorStream and do read's until they
get back -1. Most of these examples are insensitive to the
state of the Process.waitFor that happens elsewhere and sort
of rely on the -1 and the waitFor happening roughly together.
Whenever I use this technique to launch an arbitrary DOS
command (e.g. Runtime.exec("dir")), it works fine, and
everything seems to terminate as expected.
However, when my command is something like:
Runtime.exec("cmd /c start my.bat")
where I deliberately use the START command to fork off
a different process, something odd happens.
Those simple read loops get an initial burst of stdout/stderr
bytes from the "start" part of the command. But then eventually,
these loops do a "read" which blocks on those InputStreams. Now,
even if my Process.waitFor returns (because the start returned
immediately), those read loops stay blocked **until that script
started by 'start' runs to completion**. It is like the child
of the child is holding those streams open somehow.
I found that by doing something like an InputStream.available() or
a BufferedReader.ready( ) check before dropping into the read,
and allowing the Process.waitFor completion to exit those read loops,
them I get what I expect -- namely immediate return from the START,
but apparently complete copies of stdout and stderr.
Curiously, in the case where the reads block until the child process
started by START terminates, they still don't get the child's/child's
stdout and stderr. It is just a long duration thread block that
yields no data.
Can anyone explain what is happening to a
Process.getInputStream( ).read()
when the process immediately does a START and returns? Why would
the read( ) stay blocked when the START finished launching a new child
process?
... ron cain