I cannot figure out why in this case "grep -vf" is not returning the full list of items that are in file2 but not in file1. It only returns 2 of the 4 items in file2. Checked and there are no dupes but there are partial match of one item to the another item, ie(making up one): MINI and MINIMUM. I have several scripts that are using "grep -vf" and would like to understand why it's not working here. I'd really, really appreciate if someone can explain why.

As you can see file2.txt has 4 more items(lines):

$ wc -l file1.txt file2.txt
91 file1.txt
95 file2.txt
186 total
$

$ awk 'FNR==NR {hash[$0]; next} !($0 in hash)' file1.txt file2.txt
KNIGHTKNM1LSET
PDQATSLSET1
PDQIOI
CITADELCDG1LSET
$
$
As you can see with "grep -vf" two items(PDQATSLSET1 and CITADELCDG1LSET) are not matched. Why??
$ grep -vf file1.txt file2.txt
KNIGHTKNM1LSET
PDQIOI
$
After further testing, looks like when I create a new file out of file1.txt with the first 40 items(lines) and run the same "grep -vf" command: grep -vf file40.txt file2.txt, it returns all 4 items:

$ head -40 file1 > file40.txt
$ grep -vf file40.txt file2.txt |egrep "PDQATSLSET1|KNIGHTKNM1LSET|CITADELCDG1LSET|PDQIOI"
KNIGHTKNM1LSET
PDQATSLSET1
PDQIOI
CITADELCDG1LSET
$
Again, thx for anybody trying to help me with this.

Reverse the order of the files in the grep run.

Thx Syg00 but I tried that before. It doesn’t return anything

Try diff also.

The basic form alone ought to do it, but be sure to check all the options for it as they can make it display a lot of useful material.

Using grep with the -f option means that it fetches patterns from the file. So if there are any periods, asterisks, or other relevant metacharacters in the first file, then that would throw off the results.

As noted above, -f is the shortcut for --file, and unless specified otherwise that pattern will be treated as a regex. The --fixed-strings option (shortcut -F) can be used to treat the pattern as a series of strings.

The mention of partial matches also suggests that either --word-regexp or --line-regexp would be useful options. (Despite the poorly-chosen names, these apply irrespective of whether pattern is a regex or not).

obviously what you posted is not enough to answer. Better would be to give a complete example, not only a few lines from here and there. I don't really want you to post everything, a minimal example would be helpful, containing file1 and file2, your commands and your expectations.