Using jq to extract information about dependencies from package.json

Question

So I am trying to run a jq command inside a makefile to link some dependencies, and I do not understand what the line inside the do-done does. If using only echo "$$dep" I understand what's going on, but when using the full line of code ([ -f "$$dep/package.json" ] && echo "$$dep";) I seem to be lost. Does anyone have any idea? Thanks.

jq -r '.dependencies,.devDependencies|keys[]' $< | while read -r dep; do \
    [ -f "$$dep/package.json" ] && echo "$$dep"; \
done | (piping forward)

Answer 1

Since this is in a makefile , there are two things that need to be understood. First, to understand the "$$" variable ( $$dep ), see this stackoverflow question:

Makefile and use of $$

Second, to understand the ... in do ... done , remember that this is essentially equivalent to a shell conditional of the form:

if [ -f _ ] ; then echo _ ; fi

For details about the test, see eg http://wiki.bash-hackers.org/commands/classictest