all:
    mkdir out -p
    pdflatex -output-directory out parent.tex
    TEXMFOUTPUT="out:" bibtex out/parent
    pdflatex -output-directory out parent.tex
    pdflatex -output-directory out parent.tex

all:
    mkdir out -p
    TEXINPUTS="src:" pdflatex -output-directory out src/parent.tex
    BIBINPUTS="src:" BSTINPUT="out:" TEXMFOUTPUT="out:" bibtex out/parent
    TEXINPUTS="src:" pdflatex -output-directory out src/parent.tex
    TEXINPUTS="src:" pdflatex -output-directory out src/parent.tex

bibliographystyle{plain}
bibliography{bibliography}

bibtex: Not writing to  $TEXMFOUTPUT/src.blg (openout_any = p).

/usr/share/texlive/texmf/web2c/texmf.cnf (UBUNTU TEXLIVE)
/usr/share/texmf-dist/web2c/texmf.cnf (ARCH LINUX TEXLIVE)

mkdir OUT
TEXMFOUTPUT="OUT"
pdflatex --output-directory OUT myfile
bibtex OUT/myfile
pdflatex --output-directory OUT myfile
pdflatex --output-directory OUT myfile

export BIBINPUTS=/path/to/directory/of/bibfile