Quantifiers (*, +, ?) in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the asterisk (*) quantifier mean in bash regular expressions?

The asterisk (*) means "zero or more" of the preceding character or group. It matches if the pattern appears any number of times, including not at all.

beginner

Explain the plus (+) quantifier in bash regex.

The plus (+) means "one or more" of the preceding character or group. It requires at least one occurrence to match.

beginner

What does the question mark (?) quantifier do in bash regex?

The question mark (?) means "zero or one" of the preceding character or group. It matches if the pattern appears once or not at all.

intermediate

In bash scripting, how would you check if a variable contains one or more digits using regex?

You can use [[ $var =~ [0-9]+ ]] which means the variable contains one or more digits.

beginner

True or False: The regex pattern 'a*' matches the string 'bbb' in bash.

True. 'a*' matches zero or more 'a's, so it matches even if there are no 'a's, like in 'bbb'.

What does the regex quantifier '+' mean in bash?

A Exactly one occurrence

B Zero or more occurrences

C Zero or one occurrence

D One or more occurrences

The '+' quantifier matches one or more occurrences of the preceding element.

Which quantifier matches zero or more times in bash regex?

A ?

B *

C +

D {1,}

The '*' quantifier matches zero or more occurrences.

What does the '?' quantifier do in bash regex?

A Matches one or more times

B Matches zero or more times

C Matches zero or one time

D Matches exactly two times

The '?' quantifier matches zero or one occurrence of the preceding element.

Which regex pattern matches a string with zero or more 'a's?

A a*

B a?

C a+

D a{1,}

"a*" matches zero or more 'a's.

In bash, which regex would match a string with at least one digit?

A [0-9]+

B [0-9]*

C [0-9]?

D [0-9]{0}

"[0-9]+" matches one or more digits.

Describe the difference between the '*', '+', and '?' quantifiers in bash regex.

Think about how many times the pattern can appear.

How would you use a quantifier in bash to check if a variable contains an optional character?

Optional means it can be there or not.