Conditions from sh syntax to Makefile syntax - if-statement

Question

I have a certain file UPDATE.sh. The task of this file is to update my program using git merge.
UPDATE.sh:
#!/usr/bin/env bash
git fetch https://xxxxx
newUpdatesAvailable=`git diff HEAD FETCH_HEAD`
if [[ "$newUpdatesAvailable" != "" ]]
then
git branch backup
git checkout backup
git add .
git add -u
git commit -m date "+%d.%m.%Y"
git checkout master
git merge FETCH_HEAD
else
echo "No updates..."
fi
I have to write the same thing but on Make syntax.
I tried to figure out the conditions in Make, but it didn't work out for me.
Please tell me how to write this correctly in Makefile without using:
update:
./UPDATE.sh

Answer 1

Another alternative, that does not require extensive quoting, semi-colons, etc, is to take advantage of the fact that make will stop executing a rule when the exit code is non zero.
This will usually result in easier to maintain Makefile, with simpler rules.
update:
git fetch https://xxxxx
git diff -q HEAD FETCH_HEAD || { echo "No Update" ; false ; }
git branch backup
git checkout backup
git add .
git add -u
git commit -m date "+%d.%m.%Y"
git checkout master
git merge FETCH_HEAD

Answer 2

You don't need to capture the output of git diff; you just need to know if there is a diff or not. Use the -q option.
if ! git diff -q HEAD FETCH_HEAD; then
git branch backup
...
else
echo "No updates"
fi
-q suppresses output and implies --exit-code, which causes git diff to exit with a non-zero exit status if there are differences.
In a Makefile, this would be
.PHONY: update
update:
git fetch https://xxxxx
if ! git diff -q HEAD FETCH_HEAD; then \
git branch backup && \
git checkout backup && \
git add . && \
git add -u && \
git commit -m date "+%d.%m.%Y" && \
git checkout master && \
git merge FETCH_HEAD; \
else \
echo "No updates"; \
fi
The semicolons and backslashes are necessary because the entire if statement has to appear on one logical line.