Mastering the Linux cut Command: Practical Examples and Advanced Options

Introduction

The cut command is a standard utility on Linux and Unix systems used to extract specific bytes, characters, or fields from each line of a file and write the result to standard output. This guide presents practical examples that can be applied in everyday command‑line workflows.

Basic Syntax

The general form is: cut OPTION... [FILE]... Key options include: -f: select fields (default delimiter is a TAB). -d: specify a custom field delimiter. -b: select bytes, optionally as a range. -c: select characters, also supporting ranges. --complement: output all fields except those specified. --output-delimiter='delimiter': change the output field separator. --only-delimited: omit lines that do not contain the delimiter.

Using Delimiters

Combining -d and -f lets you extract columns based on a chosen separator. For example, to print the first field of /etc/passwd using a colon:

$ cut -d ':' -f1 /etc/passwd
root
bin
daemon
...

To remove the first field from a space‑separated file content.txt:

$ cut -d " " -f 1 content.txt
Ubuntu
Microsoft
OsX
Unix
FreeBSD

Extracting multiple fields, such as the first and sixth fields from /etc/passwd where the line contains /bin/bash:

$ grep "/bin/bash" /etc/passwd | cut -d ':' -f1,6
root:/root
slax:/home/slax

Complementing Selections

The --complement option outputs everything except the specified fields. The following command prints all fields except the second one from /etc/passwd:

$ grep "/bin/bash" /etc/passwd | cut -d ':' --complement -f2
root:0:0:root:/root:/bin/bash

Changing the Output Delimiter

By default, the output delimiter matches the input delimiter. Use --output-delimiter to set a different separator. For instance, replace the colon with a space:

$ cut -d: -f1,7 --output-delimiter ' ' /etc/passwd | sort | uniq -u
_apt /usr/sbin/nologin
backup /usr/sbin/nologin
...

You can also output each field on a new line by specifying $'\n' as the delimiter:

$ grep root /etc/passwd | cut -d ':' -f1,6,7 --output-delimiter=$'
'
root
/root
/bin/bash

Cutting by Character Position

Characters are counted from the start of each line. To print the first character of each line in content.txt:

$ cut -c 1 content.txt
U
M
O
U
F

To display characters 1 through 7:

$ cut -c 1-7 content.txt
Ubuntu
Microso
OsX El
Unix
FreeBSD

Extract from the second character to the end:

$ cut -c2- content.txt
buntu Linux
icrosoft Windows
sX El Capitan
ix
reeBSD

Extract the first four characters:

$ cut -c-4 content.txt
Ubun
Micr
OsX
Unix
Free

Cutting by Byte Position

Use -b with comma‑separated numbers or ranges. To extract the first three bytes of each line:

$ cut -b 1,2,3 content.txt
Ubu
Mic
OsX
Uni
Fre

To extract bytes 1‑3 and 5‑7:

$ cut -b 1-3,5-7 content.txt
Ubutu
Micoso
OsXEl
Uni
FreBSD

Combining cut with Other Commands

Cut becomes especially powerful when piped with other utilities. Example extracting user, PID, and command columns from ps output:

$ ps -L u n | tr -s " " | cut -d " " -f 2,3,14-
USER PID COMMAND
0 676 /sbin/agetty -o -p -- \u --keep-baud 115200,38400,9600 ttyS0 vt220
...

Another example retrieves memory statistics and saves them to a file:

$ free -m | tr -s ' ' | sed '/^Mem/!d' | cut -d " " -f2-4 >> memory.txt
# memory.txt now contains: 985 86 234

Conclusion

The cut command works well with many other Linux/Unix tools, allowing you to build pipelines for complex text processing. Its main limitation is the inability to specify multiple character delimiters; in such cases, preprocess the input with tr or similar utilities before using cut.