I looked up how to install multiple packages from a requirements document using pip. The answers were mostly:
pip install -r requirements.txt
What does the -r do though? I can't find an answer for this and it isn't listed when I run pip help.
Instead of pip --help, look into pip install --help:
-r, --requirement Install from the given requirements file. This option can be used multiple times.
Also see these documentation paragraphs:
-rwill search for requirement file.
pip install --help
will help you !!
If you run this command below without "-r":
pip install requirements.txt
You will get this error below:
ERROR: Could not find a version that satisfies the requirement requirements.txt (from versions: none) HINT: You are attempting to install a package literally named "requirements.txt" (which cannot exist). Consider using the '-r' flag to install the packages listed in requirements.txt ERROR: No matching distribution found for requirements.txt
Because "pip" tries to install the package "requirements.txt" instead of installing the packages listed in "requirements.txt". Of cource, the package "requirements.txt" doesn't exist in PyPI while for example, the packages "django" and "pillow" exist in PyPI:
pip install django
pip install pillow
So, to install the packages listed in "requirements.txt", you must need "-r";
pip install -r requirements.txt
You can check what "-r" means by running the command below:
pip install --help
-r, --requirement Install from the given requirements file. This option can be used multiple times.
In your case pip install -r requirements.txt will install the libraries listed in your requirements.txt file.
pip install requirements.txt
Above statement looks for a python package named requirements.txt. No such package exists. Your intention is that pip install opens the txt and reads the packages from there. The -r allows pip install to open requirements.txt and install the packages inside of it instead.
