Linux shell sed awk command (2)-awk

Linux shell sed awk command (2)-awk

awk syntax Format:

awk [Options]-F program-file [--] file ...

Options:

-F FS,--field-separator FS

Create a delimiter with FS as the input line (the default delimiter is a space or tab)

-V Var=val,--assign var=val

Before executing the procedure, set a var value of Val

-F program-file,--file Program-file

Read the awk instruction from the script file to replace the input processing script in the command arguments

-W compat,-w copyright,--compat,--traditional

Running the awk,gun extension option in compatibility mode is ignored

-W Dump-variables[=file],--dump-variables[=file]

Print global variables (variables, types, values) to a file, and automatically output to a file named Dump-variables if no file name is provided

Awk-w dump-variables=out.txt ' x=1 {print x} ' Test.txt

eg

1. Match blank lines with regular expression/^$/

awk '/^$/{print ' Blank line '} ' eth0

2. Print the line containing the hostname, without specifying an action instruction. Default action is Print

awk '/hostname/'/etc/sysconfig/network

3. Specify the script-F

(1) The contents of awk.sh are as follows:

/^$/{print "Blank line"}

(2) Awk-f awk.sh eth0

Blank Line

Blank Line

Blank Line

Blank Line

Blank Line

Records and Fields

echo Hello World ABC | awk ' {print $1,$2,$3} '

Hello World ABC

echo Hello World ABC | awk ' {print $} '

Hello World ABC

echo Hello World ABC | awk ' {print NF} '

3

echo Hello World ABC | awk ' {print $NF} '

Abc

Field delimiter

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

awk ' BEGIN {fs= ': '} {print '} ' passwd

Specify multiple separators

echo ' Hello the:world,! ' | awk ' BEGIN {fs= ' [:,] '} {print $1,$2,$3,$4} '

Built-in variables

ARGC command-line arguments

FILENAME Current input document name

FNR Current input Document

Current record number of the NR input stream

NF Current record Field number

FS Character Separator

OFS output field delimiter, default space

ORS output record delimiter, default to line feed \ n

RS input record delimiter, default to line feed \ n

Expressions and operators

Arithmetic +-*/

% fetching ^ Power operation

Self-added self-reduction

+ +--

~ Match! ~ No match

echo "Test" | awk ' x=2 {print x+3} '

Awk-f: ' $1~/root/{print $} '/etc/passwd//print root ID number

Awk-f: ' $3>500 {print '} '/etc/passwd//list user name with ID number greater than 500

　

awk Syntax rules

if (an expression)

Action

Else

Action

An if (expression) action; Else action

Eg:

Interpretation SDA4 capacity is less than 20MB alarm, otherwise display OK

df-h | grep "SDA4" | awk ' {if ($4<20000) print "Alart"; else print "OK"} '

while (condition)

Action

Syntax format:

X=1

while (i<9) {

Print $i

}

eg

awk ' I=1 {} BEGIN {while (i<=10) {++i; print i}} ' test

Do

Action

while (condition)

eg

awk ' BEGIN {do {++x;print x} while (x<=10)} ' test

for (variable; condition; counter)

Action

eg

awk ' BEGIN {for (i=1;i<=10;i++) print i} '

Function

1.rand ()

awk ' BEGIN {print rand (); Srand ();p rint srand ()} '

2.gsub (x, Y, z), sub (x, Y, z)

Awk-f: ' Gsub (/root/, "Rockycai", $ $) {print $} '/etc/passwd//Global Replace

Awk-f: ' Sub (/root/, "Rockycai", $ $) {print $} '/etc/passwd//local replacement

3.length (z)

awk ' {print length ()} '/etc/passwd//display passwd per line length

4.getline

df-h | awk ' BEGIN {print ' Disk free: '}{if (nf==1) {getline;print $3};if (nf==6) print $4} '

Linux shell sed awk command (2)-awk