To install ANTLR 4, if you don't have it already
cd /usr/local/lib
wget http://antlr.org/download/antlr-4.2-complete.jar
Note - Update it to the latest ANTLR, as of when you use it Reference
export CLASSPATH=".:/usr/local/lib/antlr-4.2-complete.jar:$CLASSPATH"
alias antlr4='java -jar /usr/local/lib/antlr-4.2-complete.jar'
alias grun='java org.antlr.v4.runtime.misc.TestRig'
grun PLSQL plsql_block -gui
<Your PLSQL Code>
Example:
declare
salary number(6);
^D