Shellscript action if two files are different

Question

I am importing a file to my server using this command:

scp zumodo@shold:/test/test/test/server.py /test/test/test/test.py~/; 

I want to restart my server if the newly imported file test.py~ differs from the test.py that already exists. How would I do this using a shellscript?

Answer 1

if ! cmp test.py test.py~ >/dev/null 2>&1 then   # restart service fi 

Breaking that down:

• cmp test.py test.py~ returns true (0) if test.py and test.py~ are identical, else false (1). You can see this in man cmp.
• ! inverts that result, so the if statement translates to "if test.py and test.py~ are different".
• The redirects >/dev/null 2>&1 send all output of cmp to null device, so you just get the true/false comparison result, without any unwanted noise on the console.