Process.= Runtime.getRuntime().exec() not working for me

Question

when im executing linux command from java its not working can any one help me about this problem.

process3 = Runtime.getRuntime().exec(new String[] {"ls",
                    "-1s", 
                     "--block-size=1",
                      TStamp+"/received/i*.*",
                      "$dir|",
                      "awk",
"'{print $2\"\\t\"$1}'",
                           ">>",
                  "./"+TStamp+"/qa/manifest_QAG.txt"});
InputStream in1 = process3.getInputStream();              
BufferedReader br1=new BufferedReader(new InputStreamReader(in1));
String line1 =null;
while((line1=br1.readLine())!=null)
{
System.out.println(line1);
}

Edit1: im trying to list the files and generate manifest in manifest_QAG.txt

Actual command works in linux:

ls -1s --block-size=1 20130328094916142/received/is*.* $dir| awk '{print $2"\t"$1}'

Edit2: im not get any exception and not even created the file manifest_QAG.txt

Edit 3:

im trying to list the files and generate manifest in manifest_QAG.txt — Civa, Mar 28 '13 at 14:58
But what is wrong ? what is the output ? is there any output ? exception maybe ? — giorashc, Mar 28 '13 at 15:09
im not even get exception and not enen created file manifest_QAG.txt — Civa, Mar 28 '13 at 15:09
can't you write all commands written in array in a single `String` ? I guess there is some error in the command syntax that you have put in the array of String — Vishal K, Mar 28 '13 at 15:18

A.H. · Answer 1 · 2013-03-28T15:37:23.010

You did not get an Exception, because the ls command is not Java and communicates not with exceptions but with error messages on STDERR and exit codes.

Actually you must understand what the shell does when you enter a command and what the command does. Therefore a shell command line like this

ls -1s --block-size=1 20130328094916142/received/is*.* $dir| awk '{print $2"\t"$1}'

is handled by the shell this way:

shell: expand that 20130328094916142/received/is*.* into a list of filenames
shell: expand the $dir part into a list of filenames
shell: execute the ls command with the arguments
- ls
- -1s
- --block-size=1
- each expanded filename as a separate argument
shell: execute awk command with the argument
- {print ...}
shell: connect the output of ls to the input of awk
ls: evaluate arguments
awk: read each line, process it with the given script and output the result.

You see: the expansion of environment variables and wildcards is done by the shell, not by ls.

Back to Java: execute does NOT process the arguments like a shell. That is up to you. Therefore your call is the shell equivalent roughly like this:

ls '-1s' '--block-size=1' '20130328094916142/received/is*.*' '$dir' '|' 'awk' '{print $2"\t"$1}'

everything is quoted, even the pipe, hence nothing is expanded by the shell.

So far the problem. What are the solutions?

You can emulate the shell and do the expansion in Java. Have fun with this. (I.e. this is not a real solution).
You can call a shell from Java instead of ls.

The later is like this:

a shell has usually a -c option where you can give it one command string which is then evaluated in the same way as a real typed command line.

So you call the command like this

String[] args = {
    "/bin/sh",
    "-c",
    "ls -1s --block-size=1 20130328094916142/received/is*.* $dir| awk '{print $2\"\t\"$1}'"
};
Process process3 = Runtime.getRuntime().exec(args);

Although the correct quoting of the awk command might need some more work.

score 0 · Answer 2 · answered Mar 28 '13 at 15:06

0

I think there is some typo here

/received/i*.* is different from one that is in linux command /received/is*.*

Hope it helps

answered Mar 28 '13 at 15:06

Jabir

2,776
1
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thats not a poblem is*.* is intersection of i*.* – Civa Mar 28 '13 at 15:08

score 0 · Accepted Answer · answered Mar 28 '13 at 15:21

0

The pipe (|) is not an arguments to ls, but a functionality of the shell. If you want to use a pipe like that with Runtime#exec, you have to start a shell instead and pass as argument the command string you want the shell to parse and execute.

Unless I am missing something, it would however probably be easier to list the directory and write the manifest using Java code instead of invoking external tools for trivial file and string operations.

answered Mar 28 '13 at 15:21

jarnbjo

33,923
7
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yes we can use the java to do it is very simple but im practising in complexity with Runtime.getRuntime().exec(); – Civa Mar 28 '13 at 15:32
May i know how to pass another shell? – Civa Mar 28 '13 at 15:42

Process.= Runtime.getRuntime().exec() not working for me

3 Answers3