[gh-11485] Replace xargs -0 with POSIX-compliant alternative

The xargs -0 option is not POSIX-compliant and is not available on AIX,
FreeBSD, and other systems. This commit replaces the use of xargs -0 in
the concat_lines function with a pure shell solution that reads
NUL-terminated strings using the read builtin with -d '' option.

The new implementation:
- Maintains the same functionality of handling special characters like
  pipes, quotes, and spaces correctly
- Avoids the non-portable xargs -0 option
- Uses a while loop with read -r -d '' to process NUL-terminated strings
- Builds the result string incrementally instead of using tr to convert
  newlines to spaces

This fix ensures that the mvn script works correctly on all POSIX-compliant
systems while preserving the behavior introduced in commit aeff353
to handle quoted pipes and other special characters in .mvn/jvm.config.

Fixes #11485

Author: gnodet

apache-maven/src/assembly/maven/bin/mvn

@@ -168,23 +168,39 @@ find_file_argument_basedir() {
 # concatenates all lines of a file and replaces variables
 concat_lines() {
   if [ -f "$1" ]; then
-    # First convert all CR to LF using tr
-    tr '\r' '\n' < "$1" | \
-    sed -e '/^$/d' -e 's/#.*$//' | \
-    # Replace LF with NUL for xargs
-    tr '\n' '\0' | \
-    # Split into words and process each argument
-    # Use -0 with NUL to avoid special behaviour on quotes
-    xargs -n 1 -0 | \
-    while read -r arg; do
-      # Replace variables first
-      arg=$(echo "$arg" | sed \
-        -e "s@\${MAVEN_PROJECTBASEDIR}@$MAVEN_PROJECTBASEDIR@g" \
-        -e "s@\$MAVEN_PROJECTBASEDIR@$MAVEN_PROJECTBASEDIR@g")
-
-      echo "$arg"
-    done | \
-    tr '\n' ' '
+    result=""
+    # Read the file line by line
+    while IFS= read -r line || [ -n "$line" ]; do
+      # Convert CR to LF
+      line=$(echo "$line" | tr '\r' '\n')
+      # Remove comments
+      line=$(echo "$line" | sed 's/#.*$//')
+      # Skip empty lines
+      [ -z "$(echo "$line" | tr -d ' \t')" ] && continue
+
+      # Process each argument in the line using eval to handle quotes
+      eval "set -- $line"
+      for arg in "$@"; do
+        # Replace variables
+        arg=$(echo "$arg" | sed \
+          -e "s@\${MAVEN_PROJECTBASEDIR}@$MAVEN_PROJECTBASEDIR@g" \
+          -e "s@\$MAVEN_PROJECTBASEDIR@$MAVEN_PROJECTBASEDIR@g")
+
+        # Quote the argument if it contains spaces or special shell characters
+        case "$arg" in
+          *[\ \|\&\;\<\>\(\)\$\`\\\"\'\~\*\?\[\]\#\~\=]*)
+            arg="\"$arg\""
+            ;;
+        esac
+
+        if [ -n "$result" ]; then
+          result="$result $arg"
+        else
+          result="$arg"
+        fi
+      done
+    done < "$1"
+    echo "$result"
   fi
 }
 

its/core-it-suite/src/test/java/org/apache/maven/it/MavenITgh11485AtSignInJvmConfigTest.java

@@ -0,0 +1,59 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.it;
+
+import java.io.File;
+import java.util.Properties;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * This is a test set for <a href="https://github.com/apache/maven/issues/11485">GH-11485</a>:
+ * Verify that @ character in .mvn/jvm.config values is handled correctly.
+ * This is important for Jenkins workspaces like workspace/project_PR-350@2
+ */
+public class MavenITgh11485AtSignInJvmConfigTest extends AbstractMavenIntegrationTestCase {
+
+    @Test
+    public void testAtSignInJvmConfig() throws Exception {
+        File testDir = extractResources("/gh-11485-at-sign");
+
+        Verifier verifier = newVerifier(testDir.getAbsolutePath());
+        verifier.addCliArgument(
+                "-Dexpression.outputFile=" + new File(testDir, "target/pom.properties").getAbsolutePath());
+        verifier.setForkJvm(true); // custom .mvn/jvm.config
+        verifier.addCliArgument("validate");
+        verifier.execute();
+        verifier.verifyErrorFreeLog();
+
+        Properties props = verifier.loadProperties("target/pom.properties");
+        String expectedPath = testDir.getAbsolutePath().replace('\\', '/');
+        assertEquals(
+                expectedPath + "/workspace@2/test",
+                props.getProperty("project.properties.pathWithAtProp").replace('\\', '/'),
+                "Path with @ character should be preserved");
+        assertEquals(
+                "value@test",
+                props.getProperty("project.properties.propWithAtProp"),
+                "Property value with @ character should be preserved");
+    }
+}
+

its/core-it-suite/src/test/resources/gh-11485-at-sign/.mvn/jvm.config

@@ -0,0 +1,2 @@
+-Dpath.with.at=${MAVEN_PROJECTBASEDIR}/workspace@2/test
+-Dprop.with.at=value@test

its/core-it-suite/src/test/resources/gh-11485-at-sign/pom.xml

@@ -0,0 +1,66 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <groupId>org.apache.maven.its.gh11485</groupId>
+  <artifactId>test</artifactId>
+  <version>1.0</version>
+  <packaging>pom</packaging>
+
+  <name>Test @ character in jvm.config</name>
+  <description>
+    Verify that @ character in jvm.config values is handled correctly.
+    This is important for Jenkins workspaces like workspace/project_PR-350@2
+  </description>
+
+  <properties>
+    <pathWithAtProp>${path.with.at}</pathWithAtProp>
+    <propWithAtProp>${prop.with.at}</propWithAtProp>
+  </properties>
+
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.apache.maven.its.plugins</groupId>
+        <artifactId>maven-it-plugin-expression</artifactId>
+        <version>2.1-SNAPSHOT</version>
+        <executions>
+          <execution>
+            <phase>validate</phase>
+            <goals>
+              <goal>eval</goal>
+            </goals>
+            <configuration>
+              <outputFile>target/pom.properties</outputFile>
+              <expressions>
+                <expression>project/properties/pathWithAtProp</expression>
+                <expression>project/properties/propWithAtProp</expression>
+              </expressions>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>
+