The cut command in Linux is a powerful text-processing tool used to extract specific columns or fields from lines of text. Its primary function is to cut out and display specified parts of each line in a file, making it invaluable for extracting columns of data from text files, such as logs or CSV files.
Syntax
The syntax of the cut command is very simple:
cut OPTION... [FILE]...OPTION: customize the behavior.FILE: Specifies the input file(s) to read data. If not specified, reads from the standard input.
Here are some commonly used options:
-b,--bytes=LIST: Select specific bytes or byte ranges.-c,--characters=LIST: Choose specific characters or character ranges.-d,--delimiter=DELIM: Set a custom delimiter character.-f,--fields=LIST: Select specific fields using a delimiter.--complement: Display everything except what you've specified.-s,--only-delimited: Print lines containing the delimiter.--output-delimiter=STRING: Specify a custom output delimiter.
Cut Command Examples
Below are detailed examples showcasing cut command with different options.
Using the -b (Bytes) Option
Extract a Single Byte:
echo "abcdefghijklmnopqrstuvwxyz" | cut -b 17
This command extracts the 17th byte ('q') from the provided string.
Extract Multiple Specific Bytes:
echo "abcdefghijklmnopqrstuvwxyz" | cut -b 1,2,3
Here, bytes 1, 2, and 3 ('abc') are selected and extracted.
Using Byte Ranges:
echo "abcdefghijklmnopqrstuvwxyz" | cut -b 1-3
This extracts a range of bytes (1 to 3, 'abc').
Multiple Byte Ranges:
It is also possible to select multiple integer ranges by separating them with commas.
echo "abcdefghijklmnopqrstuvwxyz" | cut -b 1-3,8-10
It extracts bytes in the ranges 1-3 ('abc') and 8-10 ('hij').
Selecting a Single Byte with Only Ending Position
echo "abcdefghijklmnopqrstuvwxyz" | cut -b -1
This command extracts just the first byte of the string. The -1 indicates that the range extends from the start of the line to the first byte.
Extracting from a Starting Byte to the End of the Line
echo "abcdefghijklmnopqrstuvwxyz" | cut -b 1-
This command extracts everything from the first byte to the end of the line, essentially capturing the entire string. The 1- specifies a range starting from the first byte and extending to the end of the line.
The -c (Characters) Option
The -c option functions similarly to -b and can be used interchangeably for all the examples provided above.
Utilizing -d and -f Options
Extracting Specific Fields:
uptime | cut -d "," -f 1
Using , as a delimiter, this extracts the first field from the uptime command output.
Implementing the --complement Option
Excluding Selected Fields:
uptime | cut -d "," -f 1,2 --complement
This command prints all fields except the first and second.
Using --output-delimiter Option
Changing Output Delimiter:
uptime | cut -d "," -f 1,2 --output-delimiter='~'
This example changes the input delimiter from , to ~.
Additional Practical Examples
1. Extracting the Last Field of a String
echo 'example.com' | rev | cut -d'.' -f 1 | revOutput:
com2. Getting the First Column
echo 'landscape:x:109:115::/var/lib/landscape:/usr/sbin/nologin' | cut -d: -f1Output:
landscape3. Removing Multiple Columns
echo '1column 2column 3column 4column 5column 6column' | cut -d" " -f1-2,4,6-Output:
1column 2column 4column 6colum4. Extracting Login Shells of Users
getent passwd | rev | cut -d ":" -f 1 | rev | grep -v "nologin"
This command lists the login shells of all users, excluding those with 'nologin'.
5. Listing System Users
cat /etc/passwd | cut -d ":" -f 1
This extracts usernames from /etc/passwd.
About The Author
Bobbin Zachariah
Bobbin Zachariah is an experienced Linux engineer who has been supporting infrastructure for many companies. He specializes in Shell scripting, AWS Cloud, JavaScript, and Nodejs. He has qualified Master’s degree in computer science. He holds Red Hat Certified Engineer (RHCE) certification and RedHat Enable Sysadmin.
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