"Linux Learning Notes" awk Usage summary __linux

Awk is an excellent text processing tool, one of the most powerful data processing engines available in Linux and UNIX environments.

This blog is Http://coolshell.cn/articles/9070.html's reading notes.

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//
Output by column
//
First, use

Netstat > Netstat.txt

command to redirect netstat results to Netstat.txt
The result looks something like this:

Proto recv-q send-q Local address           Foreign address         State
TCP        0      0 localhost:37745         localhost : 4730          established
TCP        0      0 localhost:48344         localhost:4730          established
TCP        0      0 localhost:4730          localhost:48344         established
TCP        0      0 localhost:48342         localhost:4730          established
TCP        0     ip-10-156-238-114.a:ssh li476-220.members:49359 Established
TCP        0      0 localhost:4730          localhost:37741         established
TCP        0      0 localhost:48340         localhost:4730          established
TCP        0      0 localhost:48341         localhost:4730          established
TCP        0      1 ip-10-156-238-114.:http 60.175.244.116:5268     fin_wait1

Now, I'm going to print the first column ($) and the fourth column ($), note that the whole line is $

awk ' {print $, $} ' Netstat.txt

The results are as follows:

Proto local  
TCP localhost:37745 TCP
localhost:48344 tcp
localhost:4730 TCP
localhost:48342
TCP Ip-10-156-238-114.a:ssh TCP
localhost:4730 tcp
localhost:48340 TCP
localhost:48341
TCP Ip-10-156-238-114.:http

//
Filter Records
//
The following filter conditions are: The value of the third column is 0 && the value of the 6th column is established

awk ' $3==0 && $6== ' established ' netstat.txt

Results:

TCP        0      0 localhost:37745         localhost:4730          established
TCP        0      0 localhost:48344         localhost:4730          established
TCP        0      0 localhost:4730          localhost:48344         established
TCP        0      0 localhost:48342         localhost:4730          established
TCP        0      0 localhost:4730          localhost:37741         Established

//
Built-in variables
//
$ current record (the contents of the entire row are stored in this variable)
$1~ $nNth field in the current record, separated by FS
FSThe input field delimiter is by default a space or tab
NF the number of fields in the current record, that is, how many columns
NR The number of records that have been read is line number, starting from 1, if there are more than one file, this value is constantly accumulating.
FNR current record number, unlike NR, this value will be the individual file's own line number
The record delimiter entered by RS, which defaults to line breaks
OFS Output field separator, default is also a space
ORS the record separator for output, which defaults to line breaks
FILENAME the name of the current input file

Examples of output line numbers:

awk ' $3==0 && $6== "established" | | nr==1 {printf "%2s%-20s%-20s%s\n", NR, $, $, $} ' Netstat.txt

Results:

1 (w/o                 servers)
 3 localhost:37745      localhost:4730       established
 4 localhost:48344      localhost : 4730       established
 5 localhost:4730       localhost:48344      established
 6 localhost:48342      localhost:4730       established
 8 localhost:4730       localhost:37741      established
 9 localhost : 48340      localhost:4730       established
localhost:48341      localhost:4730
established localhost:4730       localhost:37747      established

//
Specify separator
//

awk ' begin{fs= ': "} {print $, $ $} '/etc/passwd

Description
Begin{This inside is the statement before execution}
End {This contains the statement to be executed after all the rows have been processed}

Results:

Root 0/root
bin 1/bin
daemon 2/sbin
adm 3/VAR/ADM
LP 4/VAR/SPOOL/LPD
sync 5/sbin

Another way to write the awk command above is:

Awk-f: ' {print $, $ $} '/etc/passwd

//
Regular match
//

awk ' $ ~/est/| | nr==1 {print NR, $, $, $} ' ofs= ' \ t ' netstat.txt

The $ ~/est/portion of the above commands is a regular match. Represents the start of a regular, ~ representation pattern for the 6th column. //medium is the pattern.

1       (w/o    servers)
3       localhost:37745 localhost:4730  established
4       localhost:48344 localhost:4730  established
5       localhost:4730  localhost:48344 established
6       localhost:48342 localhost:4730  established

//
Statistics
//
Lists the size of all PHP files in the current directory (that is, the fifth column of the ls-l result)

Ls-l *.php | awk ' {print $} '

Calculates the total size of all PHP files under the current directory

Ls-l *.php | awk ' {sum+=$5} end {print sum} '

Statistics of individual connection States (note the use of arrays in them)

awk ' nr!=1{a[$6]++;} End {for (I in a) print I "," a[i];} ' Netstat.txt

To count the amount of memory consumed by each user's process

PS aux | awk ' nr!=1{a[$1]+=$6} end {for (I in a) print I, ' a[i] ' KB '} '