use strace to see what files are opened by a command

strace.sh

[sean@arch ansible]$ strace date 2>&1 | grep open
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
open("/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
open("/etc/localtime", O_RDONLY|O_CLOEXEC) = 3

[sean@arch ansible]$ strace touch foo 2>&1 | grep open
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
open("/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3
open("foo", O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK, 0666) = 3

[sean@arch ~]$ strace python -mfoo 2>&1 | grep open                                                
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3                                                   
open("/usr/lib/libpthread.so.0", O_RDONLY|O_CLOEXEC) = 3                                           
open("/usr/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3                                                 
open("/usr/lib/libpython3.6m.so.1.0", O_RDONLY|O_CLOEXEC) = 3                                      
open("/usr/lib/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3                                                
open("/usr/lib/libutil.so.1", O_RDONLY|O_CLOEXEC) = 3                                              
open("/usr/lib/libm.so.6", O_RDONLY|O_CLOEXEC) = 3                                                 
open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3                                     
open("/usr/lib/gconv/gconv-modules.cache", O_RDONLY) = -1 ENOENT (No such file or directory)       
open("/usr/lib/gconv/gconv-modules", O_RDONLY|O_CLOEXEC) = 3                                       
open("/usr/bin/pyvenv.cfg", O_RDONLY)   = -1 ENOENT (No such file or directory)                    
open("/usr/pyvenv.cfg", O_RDONLY)       = -1 ENOENT (No such file or directory)                    
open("/usr/lib/python3.6", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3                          
pen("/usr/lib/python3.6/encodings/__pycache__/__init__.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3   
open("/usr/lib/python3.6/__pycache__/codecs.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3               
open("/usr/lib/python3.6/encodings", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3                
open("/usr/lib/python3.6/encodings/__pycache__/aliases.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3    
open("/usr/lib/python3.6/encodings/__pycache__/utf_8.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3      
open("/usr/lib/python3.6/encodings/__pycache__/latin_1.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3    
open("/usr/lib/python3.6/__pycache__/io.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3                   
open("/usr/lib/python3.6/__pycache__/abc.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3                  
open("/usr/lib/python3.6/__pycache__/_weakrefset.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3          
open("/usr/lib/python3.6/__pycache__/_bootlocale.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3          
open("/usr/lib/python3.6/__pycache__/site.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3                 
open("/usr/lib/python3.6/__pycache__/os.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3                   
open("/usr/lib/python3.6/__pycache__/stat.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3                 
open("/usr/lib/python3.6/__pycache__/posixpath.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3            
open("/usr/lib/python3.6/__pycache__/genericpath.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3          
open("/usr/lib/python3.6/__pycache__/_collections_abc.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3     
open("/usr/lib/python3.6/__pycache__/_sitebuiltins.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3        
open("/usr/lib/python3.6/__pycache__/sysconfig.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3            
open("/usr/lib/python3.6/__pycache__/_sysconfigdata_m_linux_x86_64-linux-gnu.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3                                                                                  
open("/usr/lib/python3.6/site-packages", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3            
open("/usr/lib/python3.6/site-packages/matplotlib-2.0.2-py3.6-nspkg.pth", O_RDONLY|O_CLOEXEC) = 3  
open("/usr/lib/python3.6/__pycache__/types.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4                
open("/usr/lib/python3.6/__pycache__/functools.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4            
open("/usr/lib/python3.6/collections/__pycache__/__init__.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4 
open("/usr/lib/python3.6/__pycache__/operator.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4             
open("/usr/lib/python3.6/__pycache__/keyword.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4              
open("/usr/lib/python3.6/__pycache__/heapq.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4                
open("/usr/lib/python3.6/lib-dynload", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 4              
open("/usr/lib/python3.6/lib-dynload/_heapq.cpython-36m-x86_64-linux-gnu.so", O_RDONLY|O_CLOEXEC) = 4                                                                                                  
open("/usr/lib/python3.6/__pycache__/reprlib.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4              
open("/usr/lib/python3.6/__pycache__/weakref.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4              
open("/usr/lib/python3.6/collections", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 4              
open("/usr/lib/python3.6/collections/__pycache__/abc.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4      
open("/usr/lib/python3.6/importlib/__pycache__/__init__.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4   
open("/usr/lib/python3.6/__pycache__/warnings.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4             
open("/usr/lib/python3.6/importlib", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 4                
open("/usr/lib/python3.6/importlib/__pycache__/util.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4       
open("/usr/lib/python3.6/importlib/__pycache__/abc.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4        
open("/usr/lib/python3.6/importlib/__pycache__/machinery.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4  
open("/usr/lib/python3.6/__pycache__/contextlib.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 4           
open("/usr/lib/python3.6/site-packages", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 4            
open("/home/sean", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3                                  
open("/usr/lib/python3.6/__pycache__/runpy.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3                
open("/usr/lib/python3.6/__pycache__/pkgutil.cpython-36.pyc", O_RDONLY|O_CLOEXEC) = 3