Intro To 'cut' Command In Linux

2023-10-18 - By Robert Elder

I use the cut command to cut columns out of text documents. For example, in the file 'foo.txt'

cat foo.txt

a	1
b	2
c	3
d	4
e	5

I can extract the first column like this:

cut -f 1 foo.txt

a
b
c
d
e

or the second column like this:

cut -f 2 foo.txt

A Terminal-like Spreadsheet Cut Tool

The cut command could be thought of as a primitive terminal based version of performing a 'cut' operation inside of a spreadsheet program:

Extracting One Or More Columns

Here, I have a text file called 'books.txt' that contains a list of books in tab separated column format:

Tropic of Cancer	Henry Miller	1934
Housekeeping	Marilynne Robinson	1981
Deliverance	James Dickey	1970
The Sun Also Rises	Ernest Hemingway	1926
The Great Gatsby	F. Scott Fitzgerald	1925
The Corrections	Jonathan Franzen	2001
The Berlin Stories	Christopher Isherwood	1946
Call It Sleep	Henry Roth	1935
Slaughterhouse-Five	Kurt Vonnegut	1969
Light in August	William Faulkner	1932

I can use the cut command with the '-f' flag to extract each column individually by it's one-based index number:

cut -f 1 books.txt

Tropic of Cancer
Housekeeping
Deliverance
The Sun Also Rises
The Great Gatsby
The Corrections
The Berlin Stories
Call It Sleep
Slaughterhouse-Five
Light in August

cut -f 2 books.txt

Henry Miller
Marilynne Robinson
James Dickey
Ernest Hemingway
F. Scott Fitzgerald
Jonathan Franzen
Christopher Isherwood
Henry Roth
Kurt Vonnegut
William Faulkner

cut -f 3 books.txt

I can even extract multiple columns at once:

cut -f 1,3 books.txt

Tropic of Cancer	1934
Housekeeping	1981
Deliverance	1970
The Sun Also Rises	1926
The Great Gatsby	1925
The Corrections	2001
The Berlin Stories	1946
Call It Sleep	1935
Slaughterhouse-Five	1969
Light in August	1932

Using 'awk' As Alternative

Most of the use cases for the '-f' flag are made redundant by the 'awk' command which is more powerful:

cat books.txt | awk -F'\t' '{print $1"\t"$3}'

Tropic of Cancer	1934
Housekeeping	1981
Deliverance	1970
The Sun Also Rises	1926
The Great Gatsby	1925
The Corrections	2001
The Berlin Stories	1946
Call It Sleep	1935
Slaughterhouse-Five	1969
Light in August	1932

This is even pointed out in the 'cut' command's own documentation:

info cut

...
     Note ‘awk’ supports more sophisticated field processing, like
     reordering fields, and handling fields aligned with blank
     characters.  By default ‘awk’ uses (and discards) runs of blank
     characters to separate fields, and ignores leading and trailing
     blanks.
          awk '{print $2}'      # print the second field
          awk '{print $(NF-1)}' # print the penultimate field
          awk '{print $2,$1}'   # reorder the first two fields
     Note while ‘cut’ accepts field specifications in arbitrary order,
     output is always in the order encountered in the file.

     In the unlikely event that ‘awk’ is unavailable, one can use the
     ‘join’ command, to process blank characters as ‘awk’ does above.
          join -a1 -o 1.2     - /dev/null # print the second field
          join -a1 -o 1.2,1.1 - /dev/null # reorder the first two fields
...

Cut Columns By Byte Offsets

The '-b' flag can be used to extract columns based on byte offsets. Here, I have a text document named 'model-numbers.txt' that contains model numbers of products:

US-AXA-4066-2006
US-CBB-4174-2006
ER-BYA-1760-2015
KM-BDB-7051-2016
MT-ADB-2658-2003
US-BHA-3252-2002
KG-BAC-8635-2010
GT-CFB-2489-2002
FM-CEA-1980-2002
MZ-CDB-5351-2010
DM-CWA-8389-2020
BD-BBC-1912-2012
IO-CFB-6127-2018
LV-ACB-8268-2006
CM-BVB-1519-2015
US-AQB-3275-2006

The first two characters are the country code, and the last four characters are the year. I can use this cut command to extract the country code and the year together:

cut -b 1,2,3,13,14,15,16 model-numbers.txt

US-2006
US-2006
ER-2015
KM-2016
MT-2003
US-2002
KG-2010
GT-2002
FM-2002
MZ-2010
DM-2020
BD-2012
IO-2018
LV-2006
CM-2015
US-2006

And that's why the 'cut' command is my favourite Linux command.

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