Comment by gyepi

1. Since make has builtin suffix rules, the Makefile could be simplified to:

    CXX=g++

    hello: main.o factorial.o hello.o

    clean:
        rm -rf *o hello

2. Shameless plug: he didn't mention redo [1], which is simpler than make and more reliable. The comparable redo scripts to the Makefile would be:

    cat <<EOF > @all.do
    redo hello
    EOF

    cat <<EOF > hello.do
    o='main.o factorial.o hello.o'
    redo-ifchange $o
    g++ $o -o $3
    EOF

    cat <<EOF > default.o.do
    redo-ifchange $2.cpp
    g++ -c $1 -o $3
    EOF

    cat <<EOF > @clean.do
    rm -rf *o hello
    EOF

[Edit: Note that these are heredoc examples showing how to create the do scripts.]

These are just shell scripts and can be extended as much as necesary. For instance, one can create a dependency on the compiler flags with these changes:

    cat <<EOF | install -m 0755 /dev/stdin cc
    #!/bin/sh
    g++ -c "\$@"
    EOF

    # sed -i 's/^\(redo-ifchange.\+\)/\1 cc/' *.do
    # sed -i 's}g++ -c}./cc}' *.do

sed calls could be combined; separated here for readablility.

[1] https://github.com/gyepisam/redux