Bash script improvements

In

The conditional statement

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# Check if Java is installed and set the path
if [ -d "$JAVA_HOME/bin" ] ; then
    PATH="$JAVA_HOME/bin:$PATH"

Limit execution

Place logic within a script using Linux environment variables

Env var Description
$USER provides the username
$UID provides the user’s identification number (UID) of the executing user

  • User

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    # only user JBOSS1 can run this script
    if [ "$USER" != 'jboss1' ]; then
        echo "Sorry, this script must be run as JBOSS1!"
        exit 1
    fi
    echo "continue script"

  • User identification name

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    # only user ROOT can run this script, whose UID is 0
    if [ "$UID" -gt 0 ]; then
        echo "Sorry, this script must be run as ROOT!"
        exit 1
    fi
    echo "continue script"

Use arguments

  • No arguments

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    # Don't do anything if there is no argument
    if [ $# -eq 0 ]; then
        echo "No arguments provided"
        exit 1
    fi
    echo "arguments found: $#"

  • Multiple arguments

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    echo $1 $2 $3

  • Agument 0 is the name of the script being executed

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    # log the name of the script executed
    echo test >> $0.log

User input

  • Offer user input

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    echo "enter a word please:"
    read word
    echo $word

  • Offer choices to the use*

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    read -p "Install Software ?? [Y/n]: " answ
    if [ "$answ" == 'n' ]; then
        exit 1
    fi
    echo "Installation starting..."

Exit on failure

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#install JDK8: extract the file and check success before setting symbolic links
tar kxzmf jdk-8u221-linux-x64.tar.gz -C /jdk --checkpoint=.500; ec=$?
if [ $ec -ne 0 ]; then
    echo "Installation failed - exiting."
    exit 1
fi