I have two files, file1 and file2, and want to find the similarity between the two files using grep.
why -f should flow by the file name without spaces when I surround the -f file1 with quotes?
this will work
grep -i "-ffile1" file2
but this will not work
grep -i "-f file1" file2
but if I remove the quotes these two cases will work
grep -i -ffile1 file2 grep -i -f file1 file2
Advertisement
Answer
By convention, one-letter options with arguments can be either presented as two arguments, i.e. either
(1)
- Nth parameter to grep :
-f - (N+1)st parameter to grep : the filename.
or
(2)
as a single parameter, where the name immedately follows the option letter: -ffilename
In your second attempt, "-f xxxx", you are passing a single parameter (which corresponds to case (2)), but what follows immediately after the option letter, is a space. Hence you specify a file name starting with a space. Such a file does not exist. Therefore, you see a different behaviour in this case.