Grep returns no such file or directory when using multiple flags

Question

I am a beginner of bash script. I just started to write a script where it checks the contents of b.txt can all be found in a.txt. (line by line preferably). My code is as following:
grep -Ffw b.txt a.txt

As you can see, I want to do fixed string instead of REGEX, I want to check everything from the b.txt file, because there are some strings inside the b.txt and I want to check if all of them exist in a.txt. And I also want to match the whole word only of course. So these are the requirements, however when I run this command it returns me an error says:
grep: w: No such file or directory

I am thinking that maybe there are some limitations of the flags in bash? Sorry I am not really familiar with the language, didn't read much about the MAN page etc. If anyone could help me to solve the puzzle it would be appreciated :) In addition, i think if possible I would like to add a -q to surpress the output when there is a match also, right now I didn't add it in the example since it couldn't make it through with 3 flags even. So can anyone give me some hints here? Thanks in advance!

the b.txt has to follow the -f flag. So you have to write grep -Fwf b.txt a.txt or grep -wFf b.txt a.txt — kvantour
– kvantour, Commented Aug 10, 2021 at 13:13
Oh thanks, it works now :) didn't expect to be this simple though — maoyi
– maoyi, Commented Aug 10, 2021 at 13:18
do you care to give a breif explanation on why b.txt has to follow the ``-f` flag? :) Just curious — maoyi
– maoyi, Commented Aug 10, 2021 at 13:20

Dominique · Accepted Answer · 2021-08-10 13:30:40Z

1

Hereby some explanation from the manpage:

OPTIONS
   Generic Program Information
   ...
      -F, --fixed-strings
              Interpret PATTERNS as fixed strings, ...
      -f FILE, --file=FILE
              Obtain patterns from FILE, ...
      -w, --word-regexp
              Select only those lines ...

As you can see, the options -F and -w are indicated ending immediately (hence the comma in -F, and -w,), but the -f switch is followed by FILE, with means they belong together.

I you want to preserve the order Ffw, that's possible, but then you need to do something like:

grep -Ff b.txt -w a.txt

answered Aug 10, 2021 at 13:30

Dominique

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1 Comment

maoyi Over a year ago

This is really great explanation. Thank you!

maoyi · Accepted Answer · 2021-08-10 13:32:08Z

0

As mentioned by @kvantour, the solution is simply placing the -f before the b.txt file.
grep -Fwf b.txt a.txt
Should have thought it when it says 'no such file or directory' as it was a clear indication that flags after the -f were treated as the path already.

answered Aug 10, 2021 at 13:32

maoyi

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