cut (extract columns) in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the cut command do in Linux?

The cut command extracts sections from each line of input, usually columns or fields, based on delimiters or character positions.

beginner

How do you extract the first 5 characters of each line using cut?

Use cut -c 1-5 filename to get characters 1 through 5 from each line of the file.

beginner

What option do you use with cut to specify a delimiter other than the default tab?

Use -d followed by the delimiter character, for example cut -d ',' -f 2 file.csv to extract the second field separated by commas.

beginner

How do you extract the 2nd and 4th fields from a comma-separated file using cut?

Use cut -d ',' -f 2,4 filename to get the 2nd and 4th fields separated by commas.

beginner

What happens if you use cut -f 1-3 without specifying a delimiter?

By default, cut uses the tab character as the delimiter. So it extracts fields 1 to 3 separated by tabs.

Which cut option extracts characters by position?

A -d

B -f

C -c

D -s

The -c option extracts characters by position.

How do you specify a comma as the delimiter in cut?

A -d ,

B -c ,

C -f ,

D -s ,

Use -d , to specify a comma delimiter.

What does cut -f 2-4 do by default?

A Extracts characters 2 to 4

B Extracts fields 2 to 4 separated by tabs

C Extracts fields 2 to 4 separated by commas

D Extracts lines 2 to 4

By default, cut uses tab as delimiter and extracts fields 2 to 4.

Which command extracts the first 3 characters of each line?

A cut -s 1-3

B cut -f 1-3

C cut -d 1-3

D cut -c 1-3

cut -c 1-3 extracts characters 1 to 3.

What does the -s option do in cut?

A Suppress lines without delimiter

B Select specific fields

C Specify delimiter

D Extract characters

The -s option suppresses lines that do not contain the delimiter.

Explain how to use cut to extract specific fields from a comma-separated file.

Think about how to tell cut what separates the fields and which fields to get.

Describe the difference between extracting characters and extracting fields with cut.

Consider what you want to cut: fixed positions or separated parts.

Practice

1. What does the cut command do in Linux?

easy

A. Deletes files from the system

B. Changes file permissions

C. Copies files from one directory to another

D. Extracts specific columns or fields from each line of a file or input

Solution

1. Step 1: Understand the purpose of cut

   The cut command is designed to extract sections from each line of input, usually columns or fields.

2. Step 2: Compare options

   Options A, C, and D describe other commands like rm, cp, and chmod, not cut.

3. Final Answer:

   Extracts specific columns or fields from each line of a file or input -> Option D

4. Quick Check:

   cut extracts columns [OK]

Hint: Remember: cut slices columns, not files [OK]

Common Mistakes:

• Confusing cut with copy or delete commands
• Thinking cut changes file content permanently
• Assuming cut works on whole files, not lines

2. Which of the following is the correct syntax to extract the 2nd and 4th columns from a comma-separated file using cut?

easy

A. cut -d ',' -f 2,4 filename

B. cut -d ',' -f 2 4 filename

C. cut -f 2 4 -d ',' filename

D. cut -f 2-4 -d ',' filename

Solution

1. Step 1: Understand cut syntax for fields and delimiter

   The option -f specifies fields, and multiple fields must be comma-separated without spaces. The option -d sets the delimiter.

2. Step 2: Identify correct order and format

   The correct syntax places -d ',' before -f 2,4 or vice versa, but fields must be comma-separated. cut -d ',' -f 2,4 filename correctly uses -d ',' -f 2,4.

3. Final Answer:

   cut -d ',' -f 2,4 filename -> Option A

4. Quick Check:

   Fields comma-separated, delimiter set correctly [OK]

Hint: Use commas between fields and set delimiter with -d [OK]

Common Mistakes:

• Separating fields with spaces instead of commas
• Mixing order of options incorrectly
• Omitting the delimiter option for non-tab files

3. Given a file data.txt with the following content:

apple,banana,cherry,date
red,yellow,red,brown
sweet,sweet,tart,sweet

What is the output of the command cut -d ',' -f 3 data.txt?

medium

A. date
brown
sweet

B. banana
yellow
sweet

C. cherry
red
tart

D. apple
red
sweet

Solution

1. Step 1: Identify the delimiter and field number

   The delimiter is a comma, and the command extracts the 3rd field from each line.

2. Step 2: Extract the 3rd field from each line

   Line 1: 'cherry'
   Line 2: 'red'
   Line 3: 'tart'

3. Final Answer:

   cherry red tart -> Option C

4. Quick Check:

   3rd column extracted correctly [OK]

Hint: Count fields separated by delimiter, pick correct number [OK]

Common Mistakes:

• Counting fields starting at zero instead of one
• Using wrong delimiter
• Extracting wrong field number

4. You run the command cut -f 1,3 -d ':' file.txt but get no output. What is the most likely reason?

medium

A. The file is empty

B. The file uses spaces instead of ':' as delimiter

C. The fields 1 and 3 do not exist in the file

D. The cut command does not support multiple fields

Solution

1. Step 1: Check possible causes for no output

   cut produces no output if there are no lines to process.

2. Step 2: Evaluate the most likely cause

   A wrong delimiter produces modified output (whole lines with tabs), not empty. Fields 1 always exists, multiple fields supported. Empty file causes truly no output.

3. Final Answer:

   The file is empty -> Option A

4. Quick Check:

   Empty file -> no output [OK]

Hint: Verify input file has content before debugging [OK]

Common Mistakes:

• Assuming delimiter mismatch causes no output
• Thinking cut fails if fields missing
• Believing cut can't handle multiple fields

5. You have a file records.txt with tab-separated values. You want to extract the 1st and 3rd columns but only if the 3rd column is not empty. Which command correctly does this?

hard

A. cut -f 1,3 records.txt | grep -v '^\t$' | cut -f 3

B. awk -F '\t' '$3 != "" {print $1, $3}' records.txt

C. cut -f 1,3 records.txt | grep -v '^\t$'

D. cut -f 1,3 records.txt | grep '^\t$'

Solution

1. Step 1: Understand cut limitation

   cut extracts columns but cannot filter lines based on content.

2. Step 2: Use a tool that filters lines by field content

   awk can check if the 3rd field is not empty and print the 1st and 3rd fields.

3. Step 3: Analyze options

   awk -F '\t' '$3 != "" {print $1, $3}' records.txt uses awk with tab delimiter and condition $3 != "", printing fields 1 and 3 correctly.

4. Final Answer:

   awk -F '\t' '$3 != "" {print $1, $3}' records.txt -> Option B

5. Quick Check:

   Use awk to filter and extract columns [OK]

Hint: Use awk for filtering and extracting columns together [OK]

Common Mistakes:

• Trying to filter lines using cut alone
• Using grep incorrectly to filter empty fields
• Not specifying correct delimiter in awk