I am just learning sage, but there is yet another way to envoke sage that is even more bash-like. Assuming that sage is installed in "/usr/bin/sage" you can do:
$ cat ./sagetest.sage
#!/usr/bin/sage
import sys
args = len(sys.argv)
if args == 2:
arg1 = int(sys.argv[1]) # read command argument
print(arg1) # do something with command argument
f = sin(x) / x
d = diff(f, x)
show(d)
..
Note the '#!/path/to/sage' must be on the first line of the file
You must also make the file executable before it can be run the first time
$ chmod 755 ./sagetest.sage
Now you can run the file with "./sagetest.sage" or from in your PATH environment, while even with passing it arguments like in python:
$ ./ssagetest.sage 123