如何将Shell脚本输出重定向到Java控制台

Question

I have a shell script which is sending output to console

ID=$PPID
echo the process id of the parent of this script is $ID

#fetch the parent of the program which executed this shell
read PID < <(exec ps -o ppid= "$ID")
echo the grand parent id of the script is $PID

read GPID < <(exec ps -o ppid= "$PID")
echo the grand parent id of the script is $GPID


while read -u 4 P; do
 top -c -n 1 -p "$P"
done 4< <(exec pgrep -P "$PID") >&1

I am calling this script from java program and trying to display the output on console but only the output of echo is appearing. The output of top command is not appearing on the java console.

Here is my java program

import java.io.BufferedReader;

public class InformationFetcher {

    public InformationFetcher() {
    }

    public static void main(String[] args) {
    InformationFetcher informationFetcher = new InformationFetcher();
    try {
        Process process = Runtime.getRuntime().exec(
            informationFetcher.getFilePath());
        InputStream in = process.getInputStream();
        printInputStream(in);
    } catch (IOException e) {
        e.printStackTrace();
    }

    }

    private static void printInputStream(InputStream in) throws IOException {
    BufferedReader reader = new BufferedReader(new InputStreamReader(in));
    StringBuffer outBuffer = new StringBuffer();
    String newLine = System.getProperty("line.separator");
    String line;
    while ((line = reader.readLine()) != null) {
        outBuffer.append(line);
        outBuffer.append(newLine);
    }
    System.out.println(outBuffer.toString());
    }

    public String getFilePath() {
    return this.getClass().getResource("/idFetcher.sh").getPath();
    }

}

output is

the process id of the parent of this script is 3721
the grand parent id of the script is 3241
the grand parent id of the script is 3240

but it should also display output of top command. Any help would be greatly appreciated.

Answer 1

I'm not quite sure about that how top outputs, but it seems that top doesn't send its result to STDOUT in a normal way.

However, if you want top to send its result to STDOUT in a normal way, give it the -b option:

top -b -n 1
# -b means in batch mode, which outputs to `STDOUT` normally