Executing external program in Java

Question

I am trying to run "cut" inside a java program, but I am lost in terms of how to split the array of commands. My program in the command line is the following:

cut file.txt -d' ' -f1-2  > hits.txt

And I am trying to run it inside java like this

Runtime rt = Runtime.getRuntime();
Process pr = rt.exec(new String[]{"file.txt"," -d' ' -f1-2 "," > hits.txt"});
pr.waitFor();

But I get the following runtime error

Exception in thread "main" java.io.IOException: Cannot run program "cut file.txt": java.io.IOException: error=2, No such file or directory

I attribute this error to the array of Strings I am using as exec commands. Any ideas on how to do this? Also any known documentation on the issue. Thanks

It looks like either the user that runs the java process does not have permission to the file file.txt, or, more likely, file.txt is not in the same directory from where you are running the java process. You may correct the relative path or switch to an absolute path. — Brad
– Brad, Commented Mar 21, 2012 at 22:36
Is this the exact code? Shouldn't cut be in the command array? — Matt Harrison
– Matt Harrison, Commented Mar 21, 2012 at 22:38

user unknown · Accepted Answer · 2012-03-21 22:43:22Z

1

Make either an script for bash:

"/bin/bash" "-c" "cut file.txt -d' ' -f1-2  > hits.txt"

or split

"cut" "file.txt" "-d" "' '" "-f" "1-2"

The error message clearly says:

Cannot run program "cut file.txt"

so it interprets "cut file.txt" as a single programname with a blank inside.

Your problem starts with the redirection, because you can't redirect the output that way:

"cut" "file.txt" "-d" "' '" "-f" "1-2" ">" "hits.txt"

You have to handle input and output streams. It might be a better idea to implement cut in Java, to get a portable solution, or call a script which the user may specify on commandline or in a config file, so that it can be adapted for Windows or other platforms.

Calling /bin/bash and redirecting there should work - on unix like systems.

answered Mar 21, 2012 at 22:43

user unknown

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1 Comment

user unknown Over a year ago

@JulioDiaz: -c means, here follows a command. see bash --help. The command is the third String, which gets parsed as a whole script by bash.

Community · Accepted Answer · 2017-05-23 10:34:36Z

1

If you want output redirection, you have to do it yourself. > hits.txt will not do what you want. Redirecting stdout from a process called by exec is covered in another StackOverflow question.

The error you're showing isn't consistent with the source code you've listed here- there's no source for cut, for one thing. It's definitely trying to understand cut file.txt to be the complete relative path to a single executable with a space in its name, which is almost certainly not what you want. It would be easier to troubleshoot this with correct code.

edited May 23, 2017 at 10:34

CommunityBot

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answered Mar 21, 2012 at 22:38

Adam Norberg

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