How to subtract two files using grep

fileA

a

b

c

10

20

30

fileB

b

c

d

30

fileA - fileB

$ grep -F -x -v -f fileB fileA

1

10

20

shorter way

$ grep -Fxvf fileB fileA

1

10

20

man grep

...

     -F, --fixed-strings

             Interpret pattern as a set of fixed strings (i.e. force grep to behave as fgrep).

     -f file, --file=file

             Read one or more newline separated patterns from file.  Empty pattern lines match every input line.  Newlines are not considered

             part of a pattern.  If file is empty, nothing is matched.

...

     -v, --invert-match

             Selected lines are those not matching any of the specified patterns.

...

     -x, --line-regexp

             Only input lines selected against an entire fixed string or regular expression are considered to be matching lines.

...