How to use a variable in a grep regex string in a bash script

Question

I have a script that I am using to download EJBCA Community. They do something a little different where they put a minor version inside of a major version. For example EJBCA Community 6.10.0 has a minor version inside that folder of 6.10.1.2.

    #Set build (This is actually passed as a command line argument in the main script.  But for clarity I am putting it here like this.    
    EJBCA_BUILD=6.10.0
    #Check to see if standard version URL works (no minor patched version)    
    STATUS="$(curl -s --head -w %{http_code} "https://sourceforge.net/projects/ejbca/files/ejbca6/ejbca_$EJBCA_BUILD/ejbca_ce_$EJBCA_BUILD.zip" -o /dev/null)"
            echo $STATUS
            #If it doesn't exist grep to find out what the patched version is and create $EJBCA_File with the version.
            if [ $STATUS = 404 ]; then
                    EJBCA_FILE="$(curl -s -L  "https://sourceforge.net/projects/ejbca/files/ejbca6/ejbca_$EJBCA_BUILD/ejbca_ce_$EJBCA_BUILD/" | grep -o -i "ejbca_ce_$EJBCA_BUILD_[0-9].zip" | head -n1)"
                    #Bring the URL together so we can download it.
                    EJBCA_URL=https://sourceforge.net/projects/ejbca/files/ejbca6/ejbca_$EJBCA_BUILD/$EJBCA_FILE.zip
            elif [ $STATUS = 200 ]; then
                    # If it works then download it as is.
                    EJBCA_URL=https://sourceforge.net/projects/ejbca/files/ejbca6/ejbca_$EJBCA_BUILD/ejbca_ce_$EJBCA_BUILD.zip
            else
                    echo -n "There was some other error returned from the server than 404 or 200.  Exiting."
                    echo -n "The error code was $STATUS"
            exit 1
            fi

The problem I am having is specifically the grep -o -i "ejbca_ce_$EJBCA_BUILD_[0-9].zip" part. I cannot get the variable inside the regex to work. I assume this is because its parsing it incorrectly and the variable comes up empty. Any help would be greatly appreciated.

Answer 1

Use curly braces to ensure your variable name is what you intended, eg, ${EJBCA_BUILD} - in this case, I suspect that because underscore ( _ ) is a valid variable character, you are unintentionally using the variable $EJBCA_BUILD_ which is unset, so is replaced by an empty string, resulting in your grep expression being grep -o -i "ejbca_ce_[0-9].zip" which isn't what you want.

You can see this by doing a simple test in your shell:

$ EJBCA_BUILD=dummy

$ echo "ejbca_ce_$EJBCA_BUILD_[0-9].zip"
ejbca_ce_[0-9].zip

$ echo "ejbca_ce_${EJBCA_BUILD}_[0-9].zip"
ejbca_ce_dummy_[0-9].zip