th-schwarz

There are many topics around the ProcessBuilder. The focus here is how to handle the output of executed commands correctly!

The following two things are important:

• Consuming STDOUT and STDERR is necessary to avoid freezing!
• If the process writes a large amount of output, it must be consumed. This can be done by calling ProcessBuilder#redirectErrorStream, which redirects STDERR to STDOUT!

I've written a wrapper object to the ProcessBuilder to handle and configure it easier. Have look at the code below.

Here is a simple example to demonstrate the usage:

th-schwarz

#!/bin/bash
set -o nounset
set -o errexit

cd /opt/mailcow-dockerized && ./update.sh --check > /dev/null
exit_code=$?

[ $exit_code -eq 0 ] && echo -e "Subject:MAILCOW: Update available \n\n Update your mailcow instance please!\n" | sendmail root
exit 0

th-schwarz

apache2ctl -S | sed "0,/^\*:443/d" | sed -e "/ServerRoot/Q" | sed '1d' | sed 's/.*port 443 namevhost //' | sed 's/.*alias //' | awk '{print $1}' | sort

th-schwarz

ProcessBuilder pb = new ProcessBuilder("ls", "-al");
pb.directory(Paths.get("/tmp").toFile());
pb.redirectErrorStream(true);
Process process = pb.start();
try (var infoStream = process.getInputStream()) {
    infoStream.transferTo(System.out);
}
int exitCode = process.waitFor();
if(exitCode == 0)
    System.out.println("Command successful processed.");

th-schwarz

#!/bin/bash
if [ "$1" = "config" ]; then
        echo 'graph_title OpenVPN - count of users'
        echo 'graph_args --base 1000 -l 0'
        echo 'graph_vlabel count of users'
        echo 'graph_category network'
        echo 'graph_scale no'
        echo 'run.label users'
        exit 0
fi

th-schwarz

## Dumps every database to a single file, all dump files will be zipped and redirected to the stdout.
## Usage: backup-db.sh > databases.zip
##
#! /bin/bash
set -o nounset
set -o errexit

trap 'rm -rf "$BACKUP_DIR"' EXIT
BACKUP_DIR=$(mktemp -d)
MYSQL=/usr/bin/mysql