Substring extraction (${var:offset:length}) in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this substring extraction?

Given the variable assignment text="automation", what is the output of echo ${text:4:3}?

Bash Scripting

text="automation"
echo ${text:4:3}

A mat

B uto

C tom

D oma

💡 Hint

Remember that offset starts at 0 and length is how many characters to extract.

The string 'automation' indexed from 0 is: a(0) u(1) t(2) o(3) m(4) a(5) t(6) i(7) o(8) n(9). Starting at offset 4, length 3 extracts 'm', 'a', 't'.

💻 Command Output

intermediate

What happens if length exceeds string length?

Given word="script", what is the output of echo ${word:3:10}?

Bash Scripting

word="script"
echo ${word:3:10}

A pt

B ipt

C ip

D Error: length too long

💡 Hint

If length goes beyond the string end, bash extracts until the end.

Starting at offset 3 ('r'(0), 'i'(1), 'p'(2), 't'(3)), length 10 tries to extract beyond string end, but bash returns till end: 'ipt'.

📝 Syntax

advanced

Which option correctly extracts substring with negative offset?

Given data="automation", which command outputs the last 4 characters using substring extraction?

Bash Scripting

data="automation"

A echo ${data:-4:4}

B echo ${data: -4:4}

C echo ${data: -4}

D echo ${data: -4:-1}

💡 Hint

Negative offset counts from the end; length can be omitted to go to string end.

Option C uses negative offset -4 and no length, extracting last 4 chars 'tion'. Option C has a space causing syntax error. Option C uses wrong syntax. Option C has negative length which is invalid.

🔧 Debug

advanced

Why does this substring extraction fail?

Given str="automation", why does echo ${str:3,4} produce an error?

Bash Scripting

str="automation"
echo ${str:3,4}

A Comma is invalid syntax; should use colon between offset and length

B Offset 3 is out of range for this string

C Length 4 is too large and causes error

D Variable name must be uppercase

💡 Hint

Check the syntax for substring extraction carefully.

Substring extraction syntax uses colons, not commas. Using a comma causes a syntax error.

🚀 Application

expert

Extract middle word from a string using substring extraction

Given sentence="learn bash scripting easily", which command extracts the word 'bash' using substring extraction only (no external commands)?

Bash Scripting

sentence="learn bash scripting easily"

A echo ${sentence:6:4}

B echo ${sentence:6:5}

C echo ${sentence:6:3}

D echo ${sentence:7:4}

💡 Hint

Count characters including spaces to find offset and length of 'bash'.

The word 'bash' starts at offset 6 (counting from 0) and has length 4. So ${sentence:6:4} extracts 'bash'.