Bash脚本切换Java版本：现有脚本片段需补充哪些内容才能生效？

Hey there! Let's get your script working properly to switch your active Java version to the one at /usr/bin/java. First, let's break down the issues in your current snippet, then I'll share the complete, working version.

Issues in Your Current Code #

• Wrong quotation marks: You're using Chinese double quotes (”) instead of English ones ("). Bash will throw syntax errors because it doesn't recognize these non-standard quotes.
• Incorrect JAVA_HOME value: JAVA_HOME should point to the root directory of your JDK, not directly to the java executable. /usr/bin/java is usually a symbolic link to the actual executable inside a JDK folder—we need to resolve that link to get the right JAVA_HOME path.
• Broken PATH configuration: Your PATH line is missing the /bin subdirectory under JAVA_HOME, and the order is reversed. We need to put our target Java's bin folder at the start of PATH so the system prioritizes it over other installed versions.

Complete Working Script #

Here's the corrected script that handles all these issues:

#!/bin/bash

# Resolve the actual path of the /usr/bin/java executable (in case it's a symlink)
JAVA_EXEC=$(readlink -f /usr/bin/java)

# Extract the JAVA_HOME path by removing the "/bin/java" suffix
JAVA_HOME=${JAVA_EXEC%/bin/java}

# Update PATH to prioritize this Java version
export PATH="$JAVA_HOME/bin:$PATH"

# Verify the switch was successful
echo "Successfully switched to the following Java version:"
java -version
echo "JAVA_HOME has been set to: $JAVA_HOME"

How to Use This Script #

1. Save the code above as switch_java.sh in your preferred directory.
2. Give it executable permissions:

   chmod +x switch_java.sh
   

3. Run it using source (this ensures the environment variables apply to your current shell session, not just a temporary subshell):

   source switch_java.sh
   

Optional: Make the Change Permanent #

If you want this Java version to be the default every time you open a shell, add these lines to your ~/.bashrc or ~/.profile file:

JAVA_EXEC=$(readlink -f /usr/bin/java)
JAVA_HOME=${JAVA_EXEC%/bin/java}
export PATH="$JAVA_HOME/bin:$PATH"

Then run source ~/.bashrc (or source ~/.profile) to apply the change immediately.

Note for Direct Executables #

If /usr/bin/java isn't a symlink (rare, but possible), you'll need to manually find its parent JDK directory. For example, if the executable is at /usr/lib/jvm/java-17-openjdk/bin/java, set JAVA_HOME="/usr/lib/jvm/java-17-openjdk" directly instead of using the readlink step.

内容的提问来源于stack exchange，提问作者Lex