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Basic AWK usage tutorial


“Awk" command illustration on how to process input strings and get desired output.

Example below shows how "Awk" manipulates the string to get the data needed.

Below shows the output normal output listing of  "ls -l" command.

Output of  "ls"  below has "9" columns separated by space in between the columns.

"d" = In Linux if the listing starts with "d" it shows that the filename listed at the "9th" column or the last column is the name of the directiry.

"-" = In Linux if the listing starts with "-" it indicates that the data is just a regular file or not a directory of course.

Those are commonly used naming convention or indicators to determine the type of data. There are some other indicators used such as for symbolic links and hard links.

[ttxers@farmx99 honey_store]$ ls -l
total 16
drwx------ 3 branchx branchx 4096 Apr 26  2015 lists
drwx------ 3 branchx branchx 4096 Jun 30  2015 mailers
drwx------ 4 branchx branchx 4096 Apr 26  2015 spammers
drwx------ 3 branchx branchx 4096 Apr 26  2015 xmsxx


"Awk" command that prints columns 6 to 9. awk '{print $6,$7,$8,$9}'

The above awk print command can be illustrated as: awl '{print $col_number, $col_number}'

$6, $7, $8, $9 represent the columns from the ls -l output.

The "," between $6 to $9 will provide a space between each column. Or you can replace it with any  character of your choice.

[ttxers@farmx99 honey_store]$ ls -l | awk '{print $6,$7,$8,$9}'

Sample output produce by above command:

Apr 26 2015 lists
Jun 30 2015 mailers
Apr 26 2015 spammers
Apr 26 2015 xmsxx

Sort the output by month using the sort -M command.

[ttxers@farmx99 honey_store]$ ls -l | awk '{print $6,$7,$8,$9}' | sort -M

Apr 26 2015 lists
Apr 26 2015 spammers
Apr 26 2015 xmsxx
Jun 30 2015 mailers

To replace the white space and used other character use the command below:

[ttxers@farmx99 honey_store]$ ls -l | awk '{print $6 "-" $7 "-" $8 "-" $9}'

---
Apr-26-2015-lists
Jun-30-2015-mailers
Apr-26-2015-spammers
Apr-26-2015-xmsxx

Search the web for some complex examples. Start with basic and simple example to grasp the fundamental usage.

An example to delete files using Awk and Grep command.

 ls -l | grep "A001*.eml" | awk '{print $9}' |  echo  $(xargs)

 ls -l | grep "A001*.eml" | awk '{print $9}' |  rm -f  $(xargs)


Before deleting the file use the echo command to check which files are filtered by the grep command.

The rm -f will perform a force deletion without any prompt.

To delete a single file:

 ls -l | grep "2013" | awk '{print $9}' | yes | rm  A0010002.eml

Please do a test with a dummy data before executing the command in a production environment or else data loss will be the consequence.

Deletion will cause more harm than good, if not planned carefully and the person pressing the "enter" key does not exactly know what he/she is doing.



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