如何使用 Bash Shell 检查 Java 版本？

Question

I am very new to shell scripting. I want to check the following:

1. Whether the user is su or not.
2. If su then systemctl command is present or not
3. If installed then java is installed or not
4. If installed then version is 1.8 or more or not
5. If more, then it is Oracle Java or not
6. If Oracle Java then run a jar

I have done the following:

#!/bin/bash
if ! [ $(id -u) = 0 ]; then
   echo "User not logged in as Root!"
   exit 1
fi

if command -v systemctl; then
    echo Found systemctl
else
    sudo apt-get install systemd 
fi   

if type java | grep -q 'java' ; then
    echo Found java executable in PATH
    _java=java


elif [[ -n "$JAVA_HOME" ]] && [[ -x "$JAVA_HOME/bin/java" ]];  then
    echo Found java executable in JAVA_HOME     
    _java="$JAVA_HOME/bin/java"

else
    echo "Java is not installed. Please install JAVA 1.8 or upper version"
    exit 1
fi

if [ ! -z "$_java" ]; then

    version=$("$_java" -version 2>&1 | awk -F '"' '/version/ {print $2}')
    echo version "$version"
    if [ "$version" > "1.8" ]; then
        echo Java version is more than 1.8

        if [[ $("$_java" -version 2>&1) != *"Java(TM)"* ]]; then  #Problem is here
      #  if [ $("$_java" -version 2>&1) | grep -q 'Java(TM)' ]; then 
           echo "Oracle JRE is installed" 
           java -jar myJar-0.0.1-SNAPSHOT.jar
        else
           echo "Oracle JRE is not installed" ;           
        fi


    else         
        echo Java version is less than 1.8        
        echo "Please install JAVA 1.8 or upper version"
        exit 1
    fi
else
    exit 1
fi

While I am executing it, the following error is coming from the line if [[ $("$_java" -version 2>&1) != *"Java(TM)"* ]]; then if [[ $("$_java" -version 2>&1) != *"Java(TM)"* ]]; then

installNew.sh: 34: installNew.sh: [[: not found

Can anyone help?

Answer 1

Take a look at my whole script https://github.com/darshanpatidar1/Environment-Setup/blob/master/version.sh for checking versions of Java,Python and Others

#!/bin/bash
#echo "Checking java JDK version"
#command -v javac >/dev/null 2>&1 || { echo >&2 "Java JDK is not installed"; }
#variables
        purge_='sudo apt-get purge '
        update_='sudo apt update '
        install_='sudo apt install ' 

#checking for java files and exe
echo Java JRE -
if type -p java; then
    echo Found Java executable in PATH
    _java=java  
elif [[ -n $JAVA_HOME ]] && [[ -x "$JAVA_HOME/bin/java" ]];  then
    echo Found Java executable in JAVA_HOME
    _java="$JAVA_HOME/bin/java"
else
    echo "no JRE found"
fi

if [[ "$_java" ]]; then
    version=$("$_java" -version 2>&1 | awk -F '"' '/version/ {print $2}')
    echo Version "$version"
fi

echo
echo Java JDK -
if type -p javac; then
    echo Found Javac executable in PATH
    _javac=javac  
elif [[ -n $JAVA_HOME ]] && [[ -x "$JAVA_HOME/bin/javac" ]];  then
    echo Found Javac executable in JAVA_HOME
    _javac="$JAVA_HOME/bin/javac"
else
    echo "no JDK found"
    echo "Previous Java JDK files will also be removed in installation."
    read -r -p "Do you want to install it now? [y/N] " response
    if [[ "$response" =~ ^([yY][eE][sS]|[yY])+$ ]]
    then
            echo "Installing Java JDK "
        $purge_ 'java openjdk-*'
        $update_
        $install_ java -y
    else
           echo "Installation aborted !"
           exit
    fi
fi

if [[ "$_javac" ]]; then
    version=$("$_javac" -version 2>&1   | awk '{print $2}')
    echo Version "$version"
fi
#javac -version 2>&1 | head -n 1
#end of java

Answer 2

After you've sorted out the issue of the wrong shell executing your script, as glenn jackman mentioned, take caution with the line

    if [ "$version" > "1.8" ]; then

- the ordinary test command [ doesn't interpret > as the greater than operator, but rather as an output redirection, so you'll get an empty file "1.8" and, what's worse, the test yields true for any non-empty "$version". Using [[ should work as expected.