The document discusses the grep command in Linux and its uses for searching files for text patterns. Grep searches files for lines containing a specified pattern. Variants egrep and fgrep are also available. The document provides examples of using grep to search a file called "superheroes.txt" for various words and regular expressions. It also lists some basic regular expression syntax supported by grep like wildcards, character classes, and alternation.

1. Dan Morrill
Highline Community College
April 02 - 2013

2.  Superheroes.txt
 A linux computer
 Grep (already on your linux box)

3.  Grep searches the named input FILEs (or standard
input if no files are named, or the file name - is given)
for lines containing a match to the given PATTERN. By
default, grep prints the matching lines.
 In addition, two variant programs egrep and fgrep are
available. Egrep is the same as grep -E. Fgrep is the
same as grep -F.

4.  -E – extended-regexp (interpret a pattern (using a
regular expression))
 -G – basic-regexp (interpret a pattern as a basic regular
expression)
 -i – ignore case (important, linux is case sensitive)
 -n – print the line number the match was found on
 -r (-R) – recursive – search all the files under a
directory for the pattern
 -v – invert match – show all lines that are not
matching of the pattern

5.  Grep is designed to search for data in a file or in a list
(for example, when doing ps –ef |grep http)
 If you want to search for a specific item in a text
document you can also use grep to find what you are
looking for
 grep –i man superheroes.txt
 Will find everything that has the word “man” in the file
and push it to the screen for you to see.

6.  grep –i black superheroes.txt
 You should see a list of people who have the word man
in their names
 grep –i cat superheroes.txt
 You should see a list of people who have the word cat in
their names
 grep –i spider superheroes.txt
 You should see a list of people who have the word spider
in their names
 grep -v -i 'spider' heroes.txt
 You should see a list of people without the word spider
in their names

7.  . (period) – match any single character
 ^ - match the empty string at the top of the line
 $ - match the empty string at the bottom of the line
 A – match an uppercase A
 a – match a lowercase a
 d – match a digit (number)
 D – match any non-number character (a-zA-Z)
 [A-E] – match any upper case A through E (A, B, C, D, E)
 [^A-E] – match any upper case character but A through E

8.  X? – match no or one occurance of the captial letter X
 X* - match zero or more captial x’s
 X+ - match one or more captial x’s
 (abc|def)+ Match a sequence of at least one abc and
def, abc and def would both match

9.  grep –E ‘^Bat’ superheroes.txt
 Matches names that start with Bat (note the cap)
 What would I use to make it not case sensitive?
 grep -E '^(bat|Bat|cat|Cat)‘ superheroes.txt
 Matches all bat, Bat, cat, Cat in the file
 grep –i –E ‘^(bat|cat)’ superheroes.txt
 Matches all bat and cat regardless of case (similar to the
second example without so much typing)
 grep -i -E '[^b]at' superheroes.txt
 Excludes all lowercase b followed by at