What Does 'grep -liz' Do?

I love the grep linux command. It's one of those fundamental commands that I could not live without. I love it so much that I use the alias 'grepliz' for many of my social media accounts.

One day as I was just pondering the wonder that is grep, I wondered what would grep -liz do.

So here begins the idea of this blog.

-l is for listing out files

grep -l or grep --files-with-matches will only show the file names with matches and not every line or occurrence. For example, suppose we had a file called called test.txt with the following content:

Hello Grep!
Hello Grep!

if you run grep "Hello" * in the directory, the results would look like this:

$ grep "Hello" *
test.txt:Hello Grep!
test.txt:Hello Grep!

However, if you run grep -l "Hello" *, you will only get back the file name:

$ grep -l "Hello" *
test.txt

-i is for ignoring case

grep -i or grep --ignore-case
By default grep is case sensitive, using the -i flag we make it case insensitive.

For example, let's add another line to the above test.txt file so it now contains:

Hello Grep!
Hello Grep!
hello grep!

Runnning grep -i "Hello" * will show all 3 lines:

$ grep -i "Hello" *
test.txt:Hello Grep!
test.txt:Hello Grep!
test.txt:hello grep!

-Z is for zgrep

grep -Z or zgrep will search compressed files. So let's take our example test.txt file and compress it using gzip.

$ gzip test.txt 

This will produce a compressed file called test.txt.gz.
Now if you try to grep it for "Hello", it will not return any results:

$ grep "Hello" test.txt.gz

Using the -Z flag, grep will act like zgrep and uncompress the file to do the search:

$ grep -Z "Hello" test.txt.gz
Hello Grep!
Hello Grep!

According to the man pages -z and -Z should do the same thing but my tests showed otherwise. It appeared that grep wouldn't recognized a lowercase z flag.

You may be wondering what -L or -I does. I will leave that as an exercise for the reader (or perhaps another blog).

Comments

[Janardhan Pulivarthi]

There is E option too. You can search with | option like this: grep -E '(this|that)'

And one more, v option for invert. It excludes the specified word!