I want to execute shell commands from Maven's pom.xml

Solved. The problem is, executable is working in a different way in Linux. If you want to run an .sh file, you should add the exec-maven-plugin to the <plugins> section of your pom.xml file.

<plugin>
  <artifactId>exec-maven-plugin</artifactId>
  <version>3.0.0</version>
  <groupId>org.codehaus.mojo</groupId>
  <executions>
    <execution>
      <!-- Run our version calculation script -->
      <id>Renaming build artifacts</id>
      <phase>package</phase>
      <goals>
        <goal>exec</goal>
      </goals>
      <configuration>
        <executable>bash</executable>
        <commandlineArgs>handleResultJars.sh</commandlineArgs>
      </configuration>
    </execution>
  </executions>
</plugin>

2 Options:

1. You want to exec a command from maven without binding to any phase, you just type the command and maven runs it, you just want to maven to run something, you don't care if we are in compile/package/... Let's say I want to run npm start with maven, you can achieve it with the below:

mvn exec:exec -Pstart-node

For that you need the below maven section

  <profiles>
    <profile>
      <id>start-node</id>
      <build>
        <plugins>
          <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>1.3.2</version>
            <executions>
              <execution>
                <goals>
                  <goal>exec</goal>
                </goals>
              </execution>
            </executions>
            <configuration>
              <executable>npm</executable>
              <arguments><argument>start</argument></arguments>
            </configuration>
          </plugin>
        </plugins>
      </build>
    </profile>

  </profiles>

2. You want to run an arbitrary command from maven while you are at a specific phase, for example when I'm at install phase I want to run npm install you can do that with:

mvn install

And for that to work you would need the below section:

  <plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>exec-maven-plugin</artifactId>
    <version>1.3.2</version>
    <executions>

      <execution>
        <id>npm install (initialize)</id>
        <goals>
          <goal>exec</goal>
        </goals>
        <phase>initialize</phase>
        <configuration>
          <executable>npm</executable>
          <arguments>
            <argument>install</argument>
          </arguments>
        </configuration>
      </execution>

Thanks! Tomer Ben David. it helped me. as I am doing pip install in demo folder as you mentioned npm install

<groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>1.3.2</version>
            <executions>
              <execution>
                <goals>
                  <goal>exec</goal>
                </goals>
              </execution>
            </executions>
            <configuration>
              <executable>pip</executable>
              <arguments><argument>install</argument></arguments>                            
             <workingDirectory>${project.build.directory}/Demo</workingDirectory>
            </configuration>

This worked for me too. Later, I ended-up switching to the maven-antrun-plugin to avoid warnings in Eclipse. And I prefer using default plugins when possible. Example:

<plugin>
    <artifactId>maven-antrun-plugin</artifactId>
    <version>3.0.0</version>
    <executions>
        <execution>
            <id>get-the-hostname</id>
            <phase>package</phase>
            <configuration>
                <target>
                    <exec executable="bash">
                        <arg value="-c"/>
                        <arg value="hostname"/>
                    </exec>
                </target>
            </configuration>
            <goals>
                <goal>run</goal>
            </goals>
        </execution>
    </executions>
</plugin>

The accepted answer does not work in 2021 with version 3.0.0. The configuration tag inside the execution tag results in a message, "The parameter 'exectuable' is missing or invalid."

The solution was to move the configuration tag outside the executions tag.

<plugin>
  <artifactId>exec-maven-plugin</artifactId>
  <groupId>org.codehaus.mojo</groupId>
  <executions>
    <execution>
      <phase>generate-sources</phase>
      <goals>
        <goal>exec</goal>
      </goals>
    </execution>
  </executions>
  <configuration>
    <id>Version Calculation</id>
    <executable>${basedir}/scripts/calculate-version.sh</executable>
  </configuration>
</plugin>