Using GAWK in Java

SnagglezMaw · 05-27-2009, 04:40 PM

I'm writing a Java program and i need it to execute a gawk command. When I run my Java program, other command executions work just fine but it fails when it tries to do the gawk part.

The command I want to run is :

Code:

gawk '{if($4>0.9) print $3}' A261u_#.cat > tmp.dat

Where # = a number generated by other parts of the program.

My current code for running the gawk command is as follows:

Code:

Process process = 
	Runtime.getRuntime().exec("gawk '{if($4>0.9) print $3}' A261u_" 
				+ meCounter + ".cat > tmp.dat");

So basically...what am I doing wrong and how can I fix it?

ghostdog74 · 05-27-2009, 07:10 PM

Quote:

Originally Posted by SnagglezMaw

I'm writing a Java program and i need it to execute a gawk command. When I run my Java program, other command executions work just fine but it fails when it tries to do the gawk part.

The command I want to run is :

Code:

gawk '{if($4>0.9) print $3}' A261u_#.cat > tmp.dat

Where # = a number generated by other parts of the program.

My current code for running the gawk command is as follows:

Code:

Process process = 
	Runtime.getRuntime().exec("gawk '{if($4>0.9) print $3}' A261u_" 
				+ meCounter + ".cat > tmp.dat");

So basically...what am I doing wrong and how can I fix it?

if your primary tool is java, that gawk command can be implemented in Java. the gawk command basically says check the fourth field whether is it more than 0.9, if yes, print the third field. with java you can split a string too into fields. (String.split() ???) ... look up your Java documentation for exact usage.

paulsm4 · 05-27-2009, 10:18 PM

Hi -

You would also help yourself (if only for debugging purposes) to separate out a) building the command text, from b) actually running the command text.

Because the text you generate may - or may not be - the text you're expecting:

Code:

import java.io.*;

public class Test
{
  public static void main (String[] args)
  {
     int meCounter = 10;
     String sCmd = "gawk '{if($4>0.9) print $3}' A261u_" + meCounter + ".cat > tmp.dat";
     System.out.println ("sCmd=" + sCmd + "...");
     Process p = Runtime.getRuntime().exec (sCmd);
  }
}

Quote:

sCmd=gawk '{if($4>0.9) print $3}' A261u_10.cat > tmp.dat...

At this point, you'd probably:
a) Make sure "A261u_10.cat" is the file you want
b) Make sure column 4 contains a valid number
c) Make sure column 3 contains valid data
d) Make sure the previous invocation didn't overwrite your "tmp.dat"
e) etc etc

You might also want to verify that your JVM's $PATH contains "gawk".

'Hope that helps .. PSM

jan61 · 05-28-2009, 02:53 PM

Moin,

additionally:

1. Are you sure, that your current directory is the one, which contains the file you want to parse, when you call the gawk? You don't qualify the file name with a path.

2. Did you run other external commands successfully, which are using stdout redirection? I remember of some trouble when trying this in own programs.

Jan