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Editor to share with you how to use the awk command in Unix, I believe most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

The awk command not only provides simple input string filtering, but also includes extracting data columns, printing simple text, filtering content, and even doing some mathematical calculations.

If you only use awk to select specific text in a line, you may miss out on many of its features. In this article, we'll take a look at what other things awk can do for you, and provide some examples.

Extract data column

The simplest and most commonly used function provided by awk is to select specific content from data transferred by files or pipes. It is very simple to use spaces as delimiters by default.

$echo one two three four five | awk'{print $4} 'four$ who | awk' {print $1} 'jdoefhenry

A space refers to a series of space or tab characters. In the command shown below, awk filters the first and fourth items from the data provided.

The awk command can also get data from a text file by adding a filename parameter after it.

$awk'{print $1 HelenKellerQuoteThe beautiful heart.

(LCTT Note: "The best and most beautiful things in the world can not be seen or even touched, they must be felt with heart."-Helen Keller)

In this example, awk picks the first, fifth, and last fields in a row.

The $NF in the command specifies that the last field of each row is selected. This is because NF represents the number of fields in a row, Number of Field, which is 23, and $NF represents the value of that field, which is heart. The final period is also included because it is part of the last string.

Fields can be printed in any useful form. In this example, we print the field in the format of a date.

$date | awk'{print $4 Nov 2} '2019 Nov 22

If you omit the comma between field indicators in the awk command, the output will be squeezed into a string.

$date | awk'{print $4 $3 $2} '2019Nov21

If you replace the usual comma with a hyphen, awk will try to subtract the values of the two fields-maybe that's not what you want. It does not insert hyphens into the output. Instead, it does some mathematical calculations on the output.

$date | awk'{print $4 Muhami 2} '1997

In this example, it subtracts the year "2019" and the date "22" and ignores the middle "Nov".

If you want characters other than spaces as the output delimiter, you can specify the delimiter through OFS (output delimiter output field separator), like this:

$date | awk'{OFS= "-"; print $4 2019-Nov-22 print simple text

You can also use awk to simply display some text. Of course, you may want to use the echo command more than awk. But in other words, it would be useful to print some relevant text as part of the awk script. Here's a useless example:

$awk 'BEGIN {print "Hello, World"}' Hello, World

The following example is more reasonable, adding a line of text tags to better identify the data.

$who | awk 'BEGIN {print "Current logins:"} {print $1}' Current logins:shsnemo specifies the field delimiter

Not all inputs are delimited by spaces. If your text is delimited by other characters (for example, comma, colon, semicolon), you can tell awk with the-F option (enter the delimiter):

$cat testfilea:b:c,d:e$ awk-F:'{print $2jm 3} 'testfileb cpene d

Here is a more useful example of getting data from a colon-delimited / etc/passwd file:

$awk-F:'{print $1}'/ etc/passwd | head-11rootdaemonbinsyssyncgamesmanlpmailnewsuucp filter content

You can also use the awk command to evaluate fields. For example, if you just want to list the user accounts in / etc/passwd, you can filter the third field. In the following example, we only focus on UID greater than or equal to 1000:

$awk-F ":"'$3 > = 1000'/ etc/passwdnobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologinshs:x:1000:1000:Sandra Henry-Stocker,:/home/shs:/bin/bashnemo:x:1001:1001:Nemo,:/home/nemo:/usr/bin/zshdory:x:1002:1002:Dory,:/home/dory:/bin/bash...

If you want to add a title to the output, you can add a BEGIN clause:

$awk-F ":" 'BEGIN {print "user accounts:"} $3 > = 1000' / etc/passwduser accounts:nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologinshs:x:1000:1000:Sandra Henry-Stocker,:/home/shs:/bin/bashnemo:x:1001:1001:Nemo,:/home/nemo:/usr/bin/zshdory:x:1002:1002:Dory,:/home/dory:/bin/bash

If you want more than one line of headings, you can separate the output with "\ n":

$awk-F ":" 'BEGIN {print "user accounts\ n ="} $3 > = 1000' / etc/passwduser accounts=nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologinshs:x:1000:1000:Sandra Henry-Stocker,:/home/shs:/bin/bashnemo:x:1001:1001:Nemo,:/home/nemo:/usr/bin/zshdory:x:1002:1002:Dory,:/home/dory:/bin/bash for mathematical calculation in awk

Awk provides amazing mathematical computing power, and can square, calculate log, calculate tan and so on.

Here are a pair of examples:

$awk 'BEGIN {print sqrt (2019)}' 44.9333$ awk 'BEGIN {print log (2019)}' 7.61036

To learn more about awk's mathematical computing power, you can read the article "using awk to do Mathematical Computing".

Awk script

You can also write a separate set of scripts using awk. The following example mimics one previously written, but also calculates the number of accounts in the system.

#! / usr/bin/awk-f # this line is annotated BEGIN {printf "% s\ n", "User accounts:" print "=" FS= ":" nasty 0} # now start traversing data {if ($3 > = 1000) {print $1 n + +} END {print "=" print n "accounts"}

Notice how the BEGIN section provides the title, specifies the field delimiter, and initializes the counter, which is executed only during script initialization. This script also contains the END section, which runs only after all intermediate command processing is complete, showing the final number of rows of data filtered in all intermediate sections (the third field is greater than or equal to 1000).

The above is all the contents of the article "how to use awk commands in Unix". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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