Question

I have a makefile which runs commands that can take a while. I’d like those commands to be chatty if the build is initiated from an interactive shell but quieter if not (specifically, by cron). Something along the lines of (pseudocode):

foo_opts = -a -b -c
if (make was invoked from an interactive shell):
    foo_opts += --verbose

all: bar baz
    foo $(foo_opts)

This is GNU make. If the specifics of what I’m doing matter, I can edit the question.

Answer 1

It isn’t strictly determining whether it is invoked from an interactive shell or not, but for a cron job in which the output is redirected to a file, the answer to this question would be the same as for How to detect if my shell script is running through a pipe?:

if [ -t 0 ]
then
    # input is from a terminal
fi

Edit: To use this to set a variable in a Makefile (in GNU make, that is):

INTERACTIVE:=$(shell [ -t 0 ] && echo 1)

ifdef INTERACTIVE
# is a terminal
else
# cron job
endif