{"id":8504,"date":"2022-02-01T13:17:05","date_gmt":"2022-02-01T13:17:05","guid":{"rendered":"https:\/\/mailinvest.blog\/index.php\/2022\/02\/01\/how-to-use-the-linux-cut-command\/"},"modified":"2022-02-01T13:17:05","modified_gmt":"2022-02-01T13:17:05","slug":"how-to-use-the-linux-cut-command","status":"publish","type":"post","link":"https:\/\/mailinvest.blog\/index.php\/2022\/02\/01\/how-to-use-the-linux-cut-command\/","title":{"rendered":"How to Use the Linux cut Command"},"content":{"rendered":"

<\/a>\n<\/p>\n

\n
\"A
fatmawati achmad zaenuri\/Shutterstock.com<\/a><\/span><\/figcaption><\/figure>\n

The Linux cut<\/code> command lets you extract portions of text from files or data streams. It\u2019s especially useful for working with delimited data, such as CSV files<\/a>. Here\u2019s what you need to know.<\/p>\n

The cut Command<\/h2>\n

The cut<\/code> command is a veteran of the Unix<\/a> world, making its debut in 1982 as part of AT&T System III UNIX. Its purpose in life is to snip out sections of text from files or streams, according to the criteria that you set. Its syntax is as simple as its purpose, but it is this joint simplicity that makes it so useful.<\/p>\n

In the time-honored UNIX way, by combining cut<\/code> with other utilities such as grep<\/code><\/a> you can create elegant and powerful solutions to challenging problems. While there are different versions of cut<\/code>, we\u2019re going to discuss the standard GNU\/Linux version. Be aware that other versions, notably the cut<\/code> found in BSD<\/a> variants, don\u2019t include all the options described here.<\/p>\n

You can check which version is installed on your computer by issuing this command:<\/p>\n

cut --version<\/pre>\n
If you see \u201cGNU coreutils\u201d in the output you\u2019re on the version we\u2019re going to describe in this article. All versions of cut<\/code> have some of this functionality, but the Linux version has had enhancements added to it.<\/p>\n
First Steps With cut<\/h2>\n
Whether we\u2019re piping information<\/a> into cut<\/code> or using cut<\/code> to read a file<\/a>, the commands we use are the same. Anything you can do to a stream of input with cut<\/code> can be done on a line of text from a file, and\u00a0vice versa<\/em>. We can tell cut<\/code> to work with bytes, characters, or delimited fields.<\/p>\n
To select a single byte, we use the -b<\/code> (byte) option and tell cut<\/code> which byte or bytes we want. In this case, it is byte five. We\u2019re sending the string \u201chow-to geek\u201d into the cut<\/code> command with a pipe, \u201c|\u201d, from echo<\/code> .<\/p>\n
echo 'how-to geek' | cut -b 5<\/pre>\n
\"Extracting<\/p>\n
The fifth byte in that string is \u201ct\u201d, so cut<\/code> responds by printing \u201ct\u201d in the terminal window.<\/p>\n
To specify a\u00a0range<\/em>\u00a0we use a hyphen. To extract bytes 5 through to\u2014and including\u201411, we\u2019d issue this command:<\/p>\n
echo 'how-to geek' | cut -b 5-11<\/pre>\n
\"Extracting<\/p>\n
You can supply multiple single bytes or ranges by separating them with commas. To extract byte 5 and byte 11, use this command:<\/p>\n
echo 'how-to geek' | cut -b 5,11<\/pre>\n
\"Extracting<\/p>\n
To get the first letter of each word we can use this command:<\/p>\n
echo 'how-to geek' | cut -b 1,5,8<\/pre>\n
\"Extracting<\/p>\n
If you use the hyphen without a\u00a0first<\/em>\u00a0number, cut<\/code> returns everything from position 1 up to the number. If you use the hyphen without a\u00a0second<\/em>\u00a0number, cut<\/code> returns everything from the first number to the end of the stream or line.<\/p>\n
echo 'how-to geek' | cut -b -6<\/pre>\n
echo 'how-to geek' | cut -b 8-<\/pre>\n
\"Extracting<\/p>\n
Using cut With Characters<\/h2>\n
Using cut<\/code> with characters is pretty much the same as using it with bytes. In both cases, special care must be taken with complex characters. By using the -c<\/code> (character) option, we tell cut<\/code> to work in terms of characters, not bytes.<\/p>\n
echo 'how-to geek' | cut -c 1,5,8<\/pre>\n
echo 'how-to geek' | cut -c 8-11<\/pre>\n
\"Extracting<\/p>\n
These work exactly as you\u2019d expect. But take a look at this example. It\u2019s a six-letter word, so asking cut<\/code> to return the characters from one to six should return the entire word. But it doesn\u2019t. It\u2019s one character short. To see the whole word we have to ask for the characters from one to seven.<\/p>\n
echo 'pi\u00f1ata' | cut -c 1-6<\/pre>\n
echo 'pi\u00f1ata' | cut -c 1-7<\/pre>\n
\"Special<\/p>\n
The issue is the character \u201c\u00f1\u201d is actually made up out of two bytes. We can see this quite easily. We\u2019ve got a short text file<\/a> containing this line of text:<\/p>\n
cat unicode.txt<\/pre>\n
\"The<\/p>\n
We\u2019ll examine that file<\/a> with the hexdump<\/code> utility. Using the -C<\/code> (canonical) option gives us a table of hexadecimal digits with the ASCII equivalent<\/a> on the right. In the ASCII table, the \u201c\u00f1\u201d isn\u2019t shown, instead, there are dots representing two<\/em> non-printable characters. These are the bytes highlighted in the hexadecimal<\/a> table.<\/p>\n
hexdump -C unicode.txt<\/pre>\n
\"Hexdump<\/p>\n
These two bytes are used by the displaying program\u2014in this case, the Bash shell<\/a>\u2014to identify the \u201c\u00f1.\u201d Many Unicode characters<\/a> use three or more bytes to represent a single character.<\/p>\n
If we ask for character 3 or character 4 we\u2019re shown the symbol for a non-printing character. If we ask for bytes 3 and<\/em> 4, the shell interprets them as \u201c\u00f1.\u201d<\/p>\n
echo 'pi\u00f1ata' | cut -c 3<\/pre>\n
echo 'pi\u00f1ata' | cut -c 4<\/pre>\n
echo 'pi\u00f1ata' | cut -c 3-4<\/pre>\n
\"Using<\/p>\n
Using cut With Delimited Data<\/h2>\n
We can ask cut<\/code> to split lines of text using a specified delimiter. By default, cut uses a tab character but it is easy to tell it to use whatever we want. The fields in the \u201c\/etc\/passwd\u201d file are separated by colons \u201c:\u201d, so we\u2019ll use that as our delimiter and extract some text.<\/p>\n
The portions of text between the delimiters are called\u00a0fields<\/em>, and are referenced just like bytes or characters, but they\u2019re preceded by the -f<\/code> (fields) option. You can leave a space between the \u201cf\u201d and the digit, or not.<\/p>\n
The first command uses the -d<\/code> (delimiter) option to tell cut to use \u201c:\u201d as the delimiter. It\u2019s going to pull the first field out of each line in the \u201c\/etc\/passwd\u201d file. That\u2019ll be a long list so we\u2019re using head<\/code> with the -n<\/code> (number) option to show the first five responses only. The second command does the same thing but uses tail<\/code> to show us the last five responses.<\/p>\n
cut -d':' -f1 \/etc\/passwd | head -n 5<\/pre>\n
cut -d':' -f2 \/etc\/passwd | tail -n 5<\/pre>\n
\"Extracting<\/p>\n
To extract a selection of fields, list them as a comma-separated list. This command will extract fields one to three, five, and six.<\/p>\n
cut -d':' -f1-3,5,6 \/etc\/passwd | tail -n 5<\/pre>\n
\"Extracting<\/p>\n
By including grep<\/code> in the command, we can look for lines that include \u201c\/bin\/bash.\u201d The means we can list only those entries that have Bash as their default shell. That\u2019ll usually be the \u201cnormal\u201d user accounts. We\u2019ll ask for fields from one to six because the seventh field is the default shell field and we already know what that is\u2014we\u2019re searching for it.<\/p>\n
grep \"\/bin\/bash\" \/etc\/passwd | cut -d':' -f1-6<\/pre>\n
\"Extracting<\/p>\n
Another way to include all fields apart from one is to use the --complement<\/code> option. This inverts the field selection and shows everything that\u00a0hasn\u2019t<\/em>\u00a0been requested. Let\u2019s repeat the last command but only ask for field seven. Then we\u2019ll run that command again with the --complement<\/code> option.<\/p>\n
grep \"\/bin\/bash\" \/etc\/passwd | cut -d':' -f7<\/pre>\n
grep \"\/bin\/bash\" \/etc\/passwd | cut -d':' -f7 --complement<\/pre>\n
\"Using<\/p>\n
The first command finds a list of entries, but field seven gives us nothing to distinguish between them, so we don\u2019t know who the entries refer to. In the second command, by adding the --complement<\/code> option we get everything except field seven.<\/p>\n
Piping cut Into cut<\/h2>\n
Sticking with the \u201c\/etc\/passwd\u201d file, let\u2019s extract field five. This is the actual name of the user who owns the user account<\/a>.<\/p>\n
grep \"\/bin\/bash\" \/etc\/passwd | cut -d':' -f5<\/pre>\n
\"The<\/p>\n
The fifth field has subfields separated by commas. They\u2019re rarely populated so they show up as a line of commas.<\/p>\n
We can remove the commas by piping the output of the previous command into another invocation of cut<\/code> . The second instance of cut<\/code>\u00a0uses the comma \u201c,\u201d as its delimiter. The -s<\/code> (only delimited) option tells cut<\/code> to suppress results that don\u2019t have the delimiter in them at all.<\/p>\n
grep \"\/bin\/bash\" \/etc\/passwd | cut -d':' -s -f5 | cut -d',' -s -f1<\/pre>\n
\"Piping<\/p>\n
Because the root entry doesn\u2019t have comma subfields in the fifth field it is suppressed, and we get the results we\u2019re after\u2014a list of the names of the \u201creal\u201d users configured on this computer.<\/p>\n
RELATED:<\/strong> How Do Linux File Permissions Work?<\/em><\/strong><\/a><\/p>\n
The Output Delimiter<\/h2>\n
We\u2019ve got a small file with some Comma Separated Values in them. The fields in this dummy data are:<\/p>\n