grep using a file

Question

I have 2 files and I want to find the difference and output only what is not inside ex2

If use grep -Ff ex2.txt ex1.txt, it shows me a b c d, if I use the same command with -v there is not output. Why with does the first command also output d?

What would be the easiest way to do this? Is grep suitable for this? Maybe diff maybe a script that would read each line and output if it's there or not?

cat ex1.txt
a
b
c
d

cat ex2.txt
a
b
c

Edit---my output shows up like this:

cat ex2.txt
a
b
c

cat ex1.txt
a
b
c
d

grep -vf ex2.txt ex1.txt

grep -f ex2.txt ex1.txt
a
b
c
d

Answer 1

grep is not really the right tool for the job here, but a quick look at the grep manpage should help (please note that grep will vary semi-wildly between distributions, as some may use GNU by default and others may use something else).

• -F ... Fixed Strings (separated by newlines) - (Category: matcher selection)
• -f ... Filename (Category: matching control)
• -v ... Invert match (Category: matching control)

So, you might imagine that something like grep -Fvf ex2.txt ex1.txt would work. However, this is not a good solution, as it requires you to already know something about the files prior to starting. There are better tools (like variants of diff) to give you more specific and more accurate differences between files and/or directories.

Edit: Fixed strings, not Fire strings (auto-corrupt be damned)

Answer 2

Try to change the order of the files:

grep -v -f ex2.txt ex1.txt
> d

Answer 3

Cannot reproduce your error:

cat ex2.txt 
a
b
c

cat ex1.txt 
a
b
c
d

grep -vf ex2.txt ex1.txt 
d

grep -f ex2.txt ex1.txt 
a
b
c

grep -Ff ex2.txt ex1.txt 
a
b
c

grep -vFf ex2.txt ex1.txt 
d

---

grep -V
grep (GNU grep) 2.20

lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 8.5 (jessie)
Release:    8.5
Codename:   jessie

Edit (on OS X with BSD grep):

cat ex2.txt 
a
b
c

cat ex1.txt 
a
b
c
d

grep -f ex2.txt ex1.txt 
a
b
c

grep -vf ex2.txt ex1.txt 
d

grep -Ff ex2.txt ex1.txt 
a
b
c

grep -v -Ff ex2.txt ex1.txt 
d

---

grep -V
grep (BSD grep) 2.5.1-FreeBSD