Why are the pkg-config commands in the makefile not being recognized when I run the script?

I am trying to run make for an open-source project on my Debian virtual machine but I do not understand why the commands based on pkg-config are not being recognized. One of the commands is as follows: tempgui-qrps.so: tempgui-qrps.cc refpersys.hh tempgui-qrps.hh tempgui-qrps.moc.hh | $(RPS_CORE_OBJECTS) $(RPS_BUILD_CXX) $(RPS_BUILD_COMPILER_FLAGS) \ -shared -o $@ -fPIC -Wall -Wextra -O -g \ $(shell pkg-config --cflags Qt5Core Qt5Gui Qt5Widgets $(RPS_PKG_NAMES)) \ $(shell pkg-config --libs Qt5Core Qt5Gui Qt5Widgets $(RPS_PKG_NAMES)) \ -std=gnu++17 \ $< When I run make on the command line, the output corresponding to the above command looks like this: g++ -std=gnu++17 \ -shared -o tempgui-qrps.so -fPIC -Wall -Wextra -O -g \ \ \ -std=gnu++17 \ tempgui-qrps.cc When I run the make command, I also see these warnings: Package readline was not found in the pkg-config search path. Perhaps you should add the directory containing `readline.pc' to the PKG_CONFIG_PATH environment variable No package 'readline' found Package zlib was not found in the pkg-config search path. Perhaps you should add the directory containing `zlib.pc' to the PKG_CONFIG_PATH environment variable No package 'zlib' found Are both these problems (absence of packages and the pkg-config commands not being processed) related? Some of the details of pkg-config installed on my system are as follows: xxxxx@xxxx:~$ pkg-config --version 0.29 xxxx@xxxx:~$ whereis pkg-config pkg-config: /usr/bin/pkg-config /usr/lib/pkg-config.multiarch /usr/share/man/man1/pkg-config.1.gz