[regex] How can I exclude one word with grep?

I need something like:

grep ^"unwanted_word"XXXXXXXX

I've a directory with a bunch of files. I want to find all the files that DO NOT contain the string "speedup" so I successfully used the following command:

grep -iL speedup *

The -v option will show you all the lines that don't match the pattern.

grep -v ^unwanted_word

Invert match using grep -v:

grep -v "unwanted word" file pattern

grep provides '-v' or '--invert-match' option to select non-matching lines.

e.g.

grep -v 'unwanted_pattern' file_name

This will output all the lines from file file_name, which does not have 'unwanted_pattern'.

If you are searching the pattern in multiple files inside a folder, you can use the recursive search option as follows

grep -r 'wanted_pattern' * | grep -v 'unwanted_pattern'

Here grep will try to list all the occurrences of 'wanted_pattern' in all the files from within currently directory and pass it to second grep to filter out the 'unwanted_pattern'. '|' - pipe will tell shell to connect the standard output of left program (grep -r 'wanted_pattern' *) to standard input of right program (grep -v 'unwanted_pattern').

If your grep supports Perl regular expression with -P option you can do (if bash; if tcsh you'll need to escape the !):

grep -P '(?!.*unwanted_word)keyword' file

Demo:

$ cat file
foo1
foo2
foo3
foo4
bar
baz

Let us now list all foo except foo3

$ grep -P '(?!.*foo3)foo' file
foo1
foo2
foo4
$ 

I excluded the root ("/") mount point by using grep -vw "^/".

# cat /tmp/topfsfind.txt| head -4 |awk '{print $NF}'
/
/root/.m2
/root
/var

# cat /tmp/topfsfind.txt| head -4 |awk '{print $NF}' | grep -vw "^/"
/root/.m2
/root
/var

I understood the question as "How do I match a word but exclude another", for which one solution is two greps in series: First grep finding the wanted "word1", second grep excluding "word2":

grep "word1" | grep -v "word2"

In my case: I need to differentiate between "plot" and "#plot" which grep's "word" option won't do ("#" not being a alphanumerical).

Hope this helps.

The right solution is to use grep -v "word" file, with its awk equivalent:

awk '!/word/' file

However, if you happen to have a more complex situation in which you want, say, XXX to appear and YYY not to appear, then awk comes handy instead of piping several greps:

awk '/XXX/ && !/YYY/' file
#    ^^^^^    ^^^^^^
# I want it      |
#            I don't want it

You can even say something more complex. For example: I want those lines containing either XXX or YYY, but not ZZZ:

awk '(/XXX/ || /YYY/) && !/ZZZ/' file

etc.