CODEWITHSUNDEEP
shellvariablesunixexpansion
Ashish
Ashish

Reputation: 83

Double expansion of shell variable

I have a table which contains an env variable and I need to fetch the variable's value and export for another java utility from within the shell script:

    command="SELECT param_value FROM tableX WHERE param_name='ABCD';"
    #This param_value is ${PATHX} and PATHX is /home/users/pathx

    PARAM_VALUE=`sqlplus -s $CONN_STRING <<- END
    SET head off;
    set feedback off;
    ${command}
    exit;
    END`

    echo ${PARAM_VALUE} | grep -q "ERROR"
    if [ $? -eq 0 ]
    then
            echo "Failed in fetching param_value "
            exit 1
    else
            #Trimming the value fetched from DB
            PARAM_VALUE=`echo "${PARAM_VALUE}" | tr -d " " | tr -d "\n"`
            echo "Value fetched from DB=${PARAM_VALUE}" 
            #This prints ${PATHX}
            export PATH_VALUE="${PARAM_VALUE}" 
            #This is exporting PATH_VALUE as ${PATHX} instead of /home/users/pathx - WHICH IS WHERE I NEED HELP
            #If I put directly export PATH_VALUE="${PATHX}", it exports the value correctly as /home/users/pathx
    fi

After searching for options, I have tried various options like below but failed:

export PATH_VALUE="${PARAM_VALUE}"
export PATH_VALUE=`eval echo "\$${PARAM_VALUE}"`
export PATH_VALUE=$(eval \$$PARAM_VALUE)
export PATH_VALUE=${$PARAM_VALUE}
export PATH_VALUE=${!PARAM_VALUE}
export PATH_VALUE=`echo ${PARAM_VALUE}`
export PATH_VALUE=`expr ${PARAM_VALUE}`

Please suggest what can be done in this case to export the actual expanded value - /home/users/pathx.

Upvotes: 0

Views: 221

Answers (2)

KamilCuk
KamilCuk

Reputation: 141020

yes the query response is ${PATHX} and this is an environment variable which I need to expand.

You could use eval, but eval is evil, if the value is exported, do a safe envsubst:

PARAM_VALUE=$(envsubst <<<"$PARAM_VALUE")

Upvotes: 1

LeadingEdger
LeadingEdger

Reputation: 714

For it to work the way you expect, the sqlplus query response should be PATHX instead of ${PATHX}. One way to fix it is to replace

PARAM_VALUE=`echo "${PARAM_VALUE}" | tr -d " " | tr -d "\n"`

with

PARAM_VALUE=`echo "${PARAM_VALUE}" | tr -dc '[:alnum:]\n\r'`

Upvotes: 2

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