Basic regex in grep in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the command grep 'pattern' filename do?

It searches the file named filename for lines that match the given pattern and prints those lines.

beginner

What is a regular expression (regex) in the context of grep?

A regex is a special text pattern that describes a set of strings. grep uses regex to find matching text in files.

beginner

How do you use grep to search for lines that start with the word 'Hello'?

Use the caret symbol ^ to match the start of a line: grep '^Hello' filename.

beginner

What does the dot . mean in a regex pattern?

The dot . matches any single character except a newline.

intermediate

How can you search for lines containing either 'cat' or 'dog' using grep?

Use the alternation symbol \| inside quotes: grep 'cat\|dog' filename.

Which symbol in regex matches the start of a line?

A *

B $

C .

D ^

The caret symbol ^ matches the start of a line in regex.

What does the regex pattern grep 'a.b' filename match?

A Lines containing 'a' followed by any character, then 'b'

B Lines containing 'ab' only

C Lines starting with 'a' and ending with 'b'

D Lines containing 'a' or 'b'

The dot '.' matches any single character, so 'a.b' matches 'a' + any character + 'b'.

How do you tell grep to treat the pattern as a basic regex?

A Use <code>grep -E</code>

B Use <code>grep -P</code>

C Use <code>grep -G</code>

D Use <code>grep -F</code>

The -G option tells grep to use basic regular expressions (default behavior).

Which grep option allows using extended regex with alternation | without escaping?

A -E

B -F

C -P

D -G

The -E option enables extended regex, allowing alternation with | without escaping.

What does the regex symbol $ match?

A Start of a line

B End of a line

C Any character

D Zero or more repetitions

The dollar sign $ matches the end of a line in regex.

Explain how to use grep with a basic regex to find lines starting with a specific word.

Think about how to anchor your search to the line start.

Describe the difference between basic and extended regex in grep and when to use each.

Consider how you write alternation patterns.