A little test of operation and maintenance shell script (12): try out awk programming

1: Introduction to awk

Awk is an interpreted programming language designed for text processing and commonly used as a data extraction and reporting tool. It is mainly used for a variety of computing and data processing tasks; awk provides a more general computing model for processing files. A typical application example of the awk program is to convert data into formatted reports. Usually these data may be logs generated by Linux programs, and the formatted reports are a useful format for system administrators to summarize the data;

Usually awk has the following functions

1) Use variables to operate text files composed of text records and fields

2) Has arithmetic and string operators

3) Have common programming structures. Such as loops and conditions

4) Generate formatted reports

5) Define functions

6) Execute Linux commands from awk script

7) Processing the results of Linux commands

8) Handle command line parameters more skillfully

9) Easier processing of multiple input streams

2: Trial on basic usage scenarios

Prepare info.txt text file

[root@www awk]# cat info.txt
Linux - Sysadmin
Databases - Oracle, Mysql etc.
Security - Firewall, Network, Online Security etc.
Cool - Websites
Storage - NetApp, EMC etc.
Productivity - Too Many technologies to explore, no much time available

2.1: awk displays text file content

[root@www awk]# awk '{ print }' info.txt
Linux - Sysadmin
Databases - Oracle, Mysql etc.
Security - Firewall, Network, Online Security etc.
Cool - Websites
Storage - NetApp, EMC etc.
Productivity - Too Many technologies to explore, no much time available
2.2 Match records with file delimiter '-'

[root@www awk]# awk -F'-' '{ print $0 }' info.txt
Linux - Sysadmin
Databases - Oracle, Mysql etc.
Security - Firewall, Network, Online Security etc.
Cool - Websites
Storage - NetApp, EMC etc.
Productivity - Too Many technologies to explore, no much time available
[root@www awk]# awk -F'-' '{ print $1 }' info.txt
Linux
Databases
Security
Cool
Storage
Productivity
[root@www awk]# awk -F'-' '{ print $2 }' info.txt
Sysadmin
Oracle, Mysql etc.
Firewall, Network, Online Security etc.
Websites
NetApp, EMC etc.
Too Many technologies to explore, no much time available
[root@www awk]# awk -F'-' '{ print $3 }' info.txt

2.3: Match records using regular expressions

As follows, use "-" as the delimiter to match records containing "etc"

[root@www awk]# awk 'BEGIN { FS="-" } $2 ~ "etc" { print $1 }' info.txt
Databases
Security
Storage
[root@www awk]# awk 'BEGIN { FS="-" } $2 ~ "etc" { print $0 }' info.txt
Databases - Oracle, Mysql etc.
Security - Firewall, Network, Online Security etc.
Storage - NetApp, EMC etc.
[root@www awk]# awk 'BEGIN { FS="-" } $2 ~ "etc" { print $2 }' info.txt
Oracle, Mysql etc.
Firewall, Network, Online Security etc.
NetApp, EMC etc.

Three: Read awk commands from awk scripts

[root@www awk]# cat secondeAwk.awk
BEGIN {
FS="-"

}
{ print $2 }

Execute the script:

[root@www awk]# awk -f secondeAwk.awk info.txt
Sysadmin
Oracle, Mysql etc.
Firewall, Network, Online Security etc.
Websites
NetApp, EMC etc.
Too Many technologies to explore, no much time available