mirror of
https://github.com/LCTT/TranslateProject.git
synced 2025-01-04 22:00:34 +08:00
110 lines
4.5 KiB
Markdown
110 lines
4.5 KiB
Markdown
ictlyh Translating
|
|
How to Use Awk to Print Fields and Columns in File
|
|
===================================================
|
|
|
|
In this part of our [Linux Awk command series][1], we shall have a look at one of the most important features of Awk, which is field editing.
|
|
|
|
It is good to know that Awk automatically divides input lines provided to it into fields, and a field can be defined as a set of characters that are separated from other fields by an internal field separator.
|
|
|
|
|
|
>Awk Print Fields and Columns
|
|
|
|
If you are familiar with the Unix/Linux or do [bash shell programming][2], then you should know what internal field separator (IFS) variable is. The default IFS in Awk are tab and space.
|
|
|
|
This is how the idea of field separation works in Awk: when it encounters an input line, according to the IFS defined, the first set of characters is field one, which is accessed using $1, the second set of characters is field two, which is accessed using $2, the third set of characters is field three, which is accessed using $3 and so forth till the last set of character(s).
|
|
|
|
To understand this Awk field editing better, let us take a look at the examples below:
|
|
|
|
**Example 1**: I have created a text file called tecmintinfo.txt.
|
|
|
|
```
|
|
# vi tecmintinfo.txt
|
|
# cat tecmintinfo.txt
|
|
```
|
|
|
|
|
|
>Create File in Linux
|
|
|
|
Then from the command line, I try to print the first, second and third fields from the file tecmintinfo.txt using the command below:
|
|
|
|
```
|
|
$ awk '//{print $1 $2 $3 }' tecmintinfo.txt
|
|
TecMint.comisthe
|
|
```
|
|
|
|
From the output above, you can see that the characters from the first three fields are printed based on the IFS defined which is space:
|
|
|
|
- Field one which is “TecMint.com” is accessed using $1.
|
|
- Field two which is “is” is accessed using $2.
|
|
- Field three which is “the” is accessed using $3.
|
|
|
|
If you have noticed in the printed output, the field values are not separated and this is how print behaves by default.
|
|
|
|
To view the output clearly with space between the field values, you need to add (,) operator as follows:
|
|
|
|
```
|
|
$ awk '//{print $1, $2, $3; }' tecmintinfo.txt
|
|
|
|
TecMint.com is the
|
|
```
|
|
|
|
One important thing to note and always remember is that the use of ($) in Awk is different from its use in shell scripting.
|
|
|
|
Under shell scripting ($) is used to access the value of variables while in Awk ($) it is used only when accessing the contents of a field but not for accessing the value of variables.
|
|
|
|
**Example 2**: Let us take a look at one other example using a file which contains multiple lines called my_shoping.list.
|
|
|
|
```
|
|
No Item_Name Unit_Price Quantity Price
|
|
1 Mouse #20,000 1 #20,000
|
|
2 Monitor #500,000 1 #500,000
|
|
3 RAM_Chips #150,000 2 #300,000
|
|
4 Ethernet_Cables #30,000 4 #120,000
|
|
```
|
|
|
|
Say you wanted to only print Unit_Price of each item on the shopping list, you will need to run the command below:
|
|
|
|
```
|
|
$ awk '//{print $2, $3 }' my_shopping.txt
|
|
|
|
Item_Name Unit_Price
|
|
Mouse #20,000
|
|
Monitor #500,000
|
|
RAM_Chips #150,000
|
|
Ethernet_Cables #30,000
|
|
```
|
|
|
|
Awk also has a printf command that helps you to format your output is a nice way as you can see the above output is not clear enough.
|
|
|
|
Using printf to format output of the Item_Name and Unit_Price:
|
|
|
|
```
|
|
$ awk '//{printf "%-10s %s\n",$2, $3 }' my_shopping.txt
|
|
|
|
Item_Name Unit_Price
|
|
Mouse #20,000
|
|
Monitor #500,000
|
|
RAM_Chips #150,000
|
|
Ethernet_Cables #30,000
|
|
```
|
|
|
|
### Summary
|
|
|
|
Field editing is very important when using Awk to filter text or strings, it helps you get particular data in columns in a list. And always remember that the use of ($) operator in Awk is different from that in shell scripting.
|
|
|
|
I hope the article was helpful to you and for any additional information required or questions, you can post a comment in the comment section.
|
|
|
|
--------------------------------------------------------------------------------
|
|
|
|
via: http://www.tecmint.com/awk-print-fields-columns-with-space-separator/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+tecmint+%28Tecmint%3A+Linux+Howto%27s+Guide%29
|
|
|
|
作者：[Aaron Kili][a]
|
|
译者：[译者ID](https://github.com/译者ID)
|
|
校对：[校对者ID](https://github.com/校对者ID)
|
|
|
|
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
|
|
|
[a]: http://www.tecmint.com/author/aaronkili/
|
|
[1]: http://www.tecmint.com/tag/awk-command/
|
|
[2]: http://www.tecmint.com/category/bash-shell/
|