String replacement (${var/old/new}) in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the syntax ${var/old/new} do in bash scripting?

It replaces the first occurrence of the string old with new inside the variable var.

beginner

How do you replace all occurrences of a substring in a variable using bash string replacement?

Use ${var//old/new} with double slashes // to replace all occurrences of old with new.

beginner

Given text="hello world world", what is the result of ${text/world/earth}?

It replaces only the first world with earth, so the result is hello earth world.

beginner

What happens if the substring to replace is not found in the variable?

The variable remains unchanged because there is nothing to replace.

beginner

Can you use string replacement syntax to modify the original variable directly?

No, ${var/old/new} returns the modified string but does not change var unless you assign it back, like var=${var/old/new}.

What does ${var/old/new} do in bash?

A Replaces all occurrences of 'old' with 'new' in 'var'

B Deletes 'old' from 'var'

C Replaces the first occurrence of 'old' with 'new' in 'var'

D Appends 'new' to 'var'

The single slash replaces only the first occurrence of 'old' with 'new' in the variable.

How do you replace all occurrences of 'cat' with 'dog' in variable 'pet'?

A ${pet/cat/dog}

B ${pet/dog/cat}

C ${pet/cat//dog}

D ${pet//cat/dog}

Double slashes // replace all occurrences, so ${pet//cat/dog} replaces every 'cat' with 'dog'.

If name="banana", what is the result of ${name/na/NA}?

A baNAna

B banana

C baNANA

D bANAna

Only the first 'na' is replaced, so 'banana' becomes 'baNAna'.

What happens if the substring to replace is not found in the variable?

A The variable becomes empty

B The variable is unchanged

C An error is thrown

D The variable is deleted

If the substring is not found, the variable stays the same.

How do you update the variable 'text' to replace 'old' with 'new'?

A text=${text/old/new}

B ${text/old/new}

C replace text old new

D text = replace(old,new)

You must assign the result back to 'text' to update it.

Explain how to replace the first occurrence and all occurrences of a substring in a bash variable using string replacement syntax.

Think about how slashes affect replacement count.

Describe what happens if the substring to replace does not exist in the variable when using ${var/old/new}.

Consider what happens when you try to replace something not present.