Check to see if Java is installed via Bash not working

Question

I'm automating some things via bash and one of the things I wish to do is only execute a certain command if a condition is false.

I have written this little script to check the existence of java on a machine and then, if it doesn't exist, install java on the machine:

#!/bin/bash

java_path=$(which java) 
if [ "$java_path" = "/usr/bin/java" ]; then
    printf "\nJava Installed, version:\n"
    java -version
else
    printf "\nJava Not Installed, Installing...\n"
    #sudo amazon-linux-extras install java-openjdk11
    java -version
fi

My problem is that the code always goes down the else path, even though when I execute which java via commandline, I get usr/bin/java

What am I doing wrong?

`if type -P java >/dev/null; then java --version; else ....; fi` , see `help type` for more info. — Jetchisel, Jun 30 '21 at 23:03
Are you sure you get `usr/bin/java` and not `/usr/bin/java`? per the other comment, `type` is better here. — jordanm, Jun 30 '21 at 23:09
Also, no need to compare `java_home` var, just checking it's not empty should work: `if [ -n "$java_path" ]` — LMC, Jun 30 '21 at 23:20
Not to print the output to `stdout` since the exit status is enough in scripting. — Jetchisel, Jul 01 '21 at 03:19
In Unix/Linux you can have several executables in different directories but same name, so testing the absolute path will not give you a correct info. Try this `which cd` — Jetchisel, Jul 01 '21 at 03:23
@LMC If java isn't installed wouldn't the shell still return some text, thereby causing the check to always go to the if branch rather than else? — Prithvi Boinpally, Jul 01 '21 at 18:29

score 2 · Accepted Answer · answered Jul 01 '21 at 19:53

2

The exit status of which can be used in the if-else statement, no need to save the output.

if which java > /dev/null 2>&1; then
    java -version
else
    echo "Java not installed"
fi

answered Jul 01 '21 at 19:53

LMC

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score 1 · Answer 2 · answered Jul 01 '21 at 02:37

1

You can use this:

#!/bin/bash
#
if [[ $(which java) == "/usr/bin/java" ]]
then
    printf "\nJava Installed, version:\n"
    java -version
else
    printf "\nJava Not Installed, Installing...\n"
fi

Since you assume java will be in /usr/bin, you consider only the installation via the official package. You could check if the package is installed instead.

To cover all cases, you could:

check if the package is installed.
check if which java returns something.
run a find to see if it is somewhere else on the system.

answered Jul 01 '21 at 02:37

Nic3500

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Thanks, this seems to work. However (I'm new to bash) why are there double square brackets in the if condition? – Prithvi Boinpally Jul 01 '21 at 03:18
Many threads explain it, start with this one: https://stackoverflow.com/questions/3427872/whats-the-difference-between-and-in-bash – Nic3500 Jul 01 '21 at 07:34
Got it. However, upon running your code, it's still printing "Java Not installed", even though it is. – Prithvi Boinpally Jul 01 '21 at 17:44
Also I tried changing "$(which java)" to "/usr/bin/java" to make sure string comparison is working and it is. – Prithvi Boinpally Jul 01 '21 at 18:30
What does `which java` return? You might have to modify the comparison text to match that particular value. – Nic3500 Jul 08 '21 at 17:18

Check to see if Java is installed via Bash not working

2 Answers2