Question

Is it possible to make lein uberjar not create a jar if no changes have been made since the previous jar was made?

Either as a feature of leiningen or with some bash scripting?

My specific use case is that I’m calling lein from within a CMake build system of a larger project.

execute_process(COMMAND lein uberjar
                WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR})

All the C++ sources are skipped if they haven’t changed, but uberjars keep being made.

Answer 1

The find command will allow you to find all files that are newer than another file.

A script built on that might look something like this:

#!/bin/sh

UBERJAR=*-standalone.jar

if [ -f ${UBERJAR} ]; then
     modified_files=$(find src project.clj -newer ${UBERJAR})

     if [ ${#modified_files} -eq 0 ]; then
         echo "Skipping uberjar because no files modified"
         exit 0
     fi  
fi  

lein uberjar

If your project has snapshot dependencies you will skip the check that determines whether you should update your snapshots from the central repo.

I suspect you’d be better off just taking the hit of building the uberjar everytime.