Master Linux Regex: Practical grep Examples for Powerful Text Search

Regular expressions are character patterns used to match specific strings during search operations.

In Linux, metacharacters are divided into two categories:

Shell metacharacters, parsed by the Linux shell.

Regex metacharacters, parsed by tools such as vi, grep, sed, and awk.

To enable colored output for grep, set the alias: alias grep='grep --color=auto' Create a test file re-file with the following content:

cat re-file
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the
groove.

Regex Metacharacters

Special metacharacters:

Extended regular expressions:

Practical Exercises

Match all lines starting with "love":

grep '^love' re-file
love, how much I adore you. Do you know

Match lines ending with "love":

grep 'love$' re-file
clover. Did you see them?  I can only hope love.

Match lines where the first character is "l", followed by any two characters, ending with "e":

grep 'l..e' re-file
I had a lovely time on our little picnic.
love, how much I adore you. Do you know
the extent of my love? Oh, by the way, I think
I lost my gloves somewhere out in that field of
clover. Did you see them?  I can only hope love.
is forever. I live for you. It's hard to get back in the

Match zero or more spaces before "love":

grep ' *love' re-file
I had a lovely time on our little picnic.
love, how much I adore you. Do you know
...

Match "love" or "Love" (case‑insensitive for the first letter):

grep '[Ll]ove' re-file  # case‑insensitive for L
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
love, how much I adore you. Do you know
...

Match an uppercase letter followed by "ove":

grep '[A-Z]ove' re-file
Lovers were all around us. It is springtime. Oh

Match any line containing characters outside the range A‑Z (i.e., all lowercase lines):

grep '[^A-Z]' re-file
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
...

Match the literal string "love.":

grep 'love\.' re-file
clover. Did you see them?  I can only hope love.

Match empty lines: grep '^$' re-file Match any character (.*):

grep '.*' re-file
I had a lovely time on our little picnic.
Lovers were all around us. It is springtime. Oh
...

Match the character "o" repeated 2 to 4 times:

grep 'o\{2,4\}' re-file
groove.

Match the character "o" repeated at least 2 times:

grep 'o\{2,\}' re-file
groove.

Match the character "o" repeated at most 2 times:

grep 'o\{,2\}' re-file
I had a lovely time on our little picnic.
...

Match one or more occurrences of the preceding character:

egrep "go+d" linux.txt
Linux is a good
god assdxw bcvnbvbjk
gooodfs awrerdxxhkl
good

Match zero or one occurrence of the preceding character:

egrep "go?d" linux.txt
god assdxw bcvnbvbjk
gdsystem awxxxx

Match either of multiple strings (alternation):

egrep "gd|good" linux.txt
Linux is a good
gdsystem awxxxx
good

Group filtering with alternation:

egrep "g(la|oo)d" linux.txt
Linux is a good
glad
good