Extended regex (grep -E) in Bash Scripting - 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, allowing more powerful pattern matching like +, ?, | without escaping.

beginner

Which symbol in extended regex means 'one or more' of the previous character or group?

The + symbol means 'one or more' of the previous character or group in extended regex.

beginner

How do you search for lines containing either 'cat' or 'dog' using grep -E?

Use the pattern cat|dog with grep -E. For example: grep -E 'cat|dog' filename finds lines with 'cat' or 'dog'.

intermediate

What is the difference between grep and grep -E?

grep uses basic regular expressions where some symbols like +, ?, | need escaping. grep -E uses extended regex where these symbols work directly.

intermediate

Write a grep -E command to find lines with a digit repeated 3 times in a row.

Use the pattern [0-9]{3} with grep -E. Example: grep -E '[0-9]{3}' filename finds lines with three digits in a row.

What does the pattern a+b match in grep -E?

A Zero or more 'a' followed by 'b'

B The characters 'a', '+', and 'b' literally

C Exactly one 'a' followed by 'b'

D One or more 'a' followed by 'b'

In extended regex, '+' means one or more of the previous character. So a+b matches one or more 'a' followed by 'b'.

Which command uses extended regex to find lines with 'cat' or 'dog'?

A grep 'cat|dog' filename

B grep -E 'cat|dog' filename

C grep -e 'cat|dog' filename

D grep -F 'cat|dog' filename

grep -E enables extended regex, so the '|' operator works as OR.

In grep -E, what does ? mean?

A Exactly one of the previous character

B One or more of the previous character

C Zero or one of the previous character

D Matches a question mark literally

The '?' quantifier means zero or one occurrence of the previous character or group.

How do you match exactly 4 digits in a row using grep -E?

A <code>[0-9]{4}</code>

B <code>[0-9]+4</code>

C <code>[0-9]{,4}</code>

D <code>[0-9]{4,}</code>

Curly braces specify exact repetition count. {4} means exactly 4 times.

Which of these is NOT a feature of extended regex in grep -E?

A Using '\d' for digit shorthand

B Using '|' for OR

C Using '+' for one or more

D Using '?' for zero or one

The '\d' shorthand is not supported in basic or extended grep regex; it requires Perl regex or other tools.

Explain how to use grep -E to search for multiple patterns with OR logic.

Think about how extended regex lets you use | without escaping.

Describe the main quantifiers available in extended regex and how they change pattern matching.

Quantifiers control how many times a character or group repeats.