grep with regex (-E) in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the -E option do in the grep command?

The -E option tells grep to use extended regular expressions (ERE), allowing more powerful pattern matching without needing to escape some special characters.

beginner

How is grep -E different from basic grep?

Basic grep uses basic regular expressions (BRE) where some characters like ?, +, and {} need escaping. grep -E uses extended regex where these characters work directly.

beginner

Example: What does grep -E 'cat|dog' file.txt do?

It searches file.txt for lines containing either 'cat' or 'dog'. The | means OR in extended regex.

intermediate

Why use grep -E instead of egrep?

egrep is an older command equivalent to grep -E. Modern systems recommend using grep -E because egrep may be deprecated.

beginner

How to match one or more digits using grep -E?

Use grep -E '[0-9]+'. The + means 'one or more' of the previous character or group.

What does the command grep -E 'a+b' file.txt match?

A Lines with 'a+b' literally

B Lines with 'a' or 'b'

C Lines with 'ab' only

D Lines with one or more 'a' followed by 'b'

The + means one or more 'a's before 'b' in extended regex.

Which symbol means OR in grep -E regex?

A *

B |

C ?

D .

The pipe | means OR in extended regular expressions.

What is the difference between grep and grep -E?

A <code>grep -E</code> only works on files

B <code>grep</code> is faster

C <code>grep -E</code> uses extended regex, <code>grep</code> uses basic regex

D No difference

grep -E enables extended regex features.

Which command is recommended for extended regex searching?

A grep -E

B grep -P

C grep -B

D egrep

grep -E is the modern recommended way to use extended regex.

How to match zero or one occurrence of 'a' using grep -E?

A a?

B a*

C a+

D a|

The ? means zero or one occurrence in extended regex.

Explain how to use grep -E to search for lines containing either 'apple' or 'orange' in a file.

Think about how to combine two words with OR in regex.

Describe the difference between basic and extended regular expressions in the context of grep.

Focus on special characters and how they behave.