Linux basic awk simple to use

awk Basic usage:

awk [Options] ' program ' file1 file2

program:pattern{ACTION STATEMENT} is made up of statements, and the statement delimiter is a semicolon

Action:print, printf

option:-F: Indicates the input field delimiter

-V var=value: variable Assignment

One,awk output command print

Print item1,item2, ...

Points:

(1) each item is separated by commas, and the output is separated by an output delimiter;

(2) each item of the output can be a string or numeric value, a field ($n) of the current record, a variable, or an expression of awk, and the value is implicitly converted to a character for output;

(3) If the item after print is omitted, it is equivalent to print$0; output "blank", using print "";

Second, the variable

1. Built-in variables

FS: Input delimiter, default is white space character

RS:The input recordseparator defaults to line breaks

Ofs:the output field separator, default to white space character

Ors:the Output Record separator, default to line break

NF: Number of fields

NR: Number of rows, uniform count of all files

FNR: Number of rows, each file Count

FileName: Current file name

ARGC: Number of command line arguments

ARGV: Array of command-line arguments

2. Custom Variables

-V var=value: variable name distinguishes character case

(1) variable can be defined in program

(2) defining variables with the-v option

Third,the printf command

format:printf formatitem1,item2

Important:1. Format is a must

2, does not wrap automatically, you need to explicitly give a row delimiter

3. Format needs to specify one for each subsequent item

format characters: All begin with % , followed by a character

%c: ASCII code for displaying characters

%d,%i: displaying decimal integers

%e,%e: Scientific notation displays values

%f: Displayed as a floating-point number

%s: String

%g,%g: Displaying values in scientific notation format or floating-point number format

%u: unsigned integer

Percent: Show % itself

Modifier:

#[.#]: First # display width, second # display precision For example:%3.2s

-: Indicates left alignment%-3d to left

+: Display numeric symbols

Four, the operator:

Arithmetic operators:

+,-,*,/,%

-X: Negative value

+x: convert to numeric

String manipulation: String connection

Assignment operators:

=,+=,-=,*=,/=,%=,^=,+ +,--

Comparison operators:

>,<,>=,<=, = =, ! =

Pattern match:~

logical operators:&& | |

Conditional expression:? ：

function Call:function_name (argu1,argu2,....)

Example:awk-f: ' {$3>=500?usertype= ' common user ': usertype= "Sysuser oradmin";p rintf "%20s:%-s\n", $1,usertype} ' /etc/passwd

Five, PATTERN

1./regularexpression/: Only the rows that are matched to the /regular expression/ are processed

2,relationalexpression: The relationship expression, there is true and false, generally speaking, not 0 or non-empty string is true, otherwise false

3,line ranges: range, similar to sed or vim address bound method

4.gegin/end: Executes only once before or after awk runs the program

5,empty: null mode, matching any row

Six, the commonly used acion

1.expression

2.Control Statements

3,compound statements

4.Input Statements

5.Output Statements

Seven, control statements

if (condition) statement [Else statement]

while (condition) statement

Do Statementwhile (condition)

for (EXPR1;EXPR2; expr3) statement

for (var in array) statement

Break

Continue

Delete Array[index]

Delete array

Exit [expression]

{statements}

7.1 If-else

Syntax:if (condition) statement [Else statement]

if (condition) {statements;} [Else {statements;}]

# awk-f: ' {if ($3>=500) print $, "is a common user."} '/etc/passwd

# awk-f: ' {if ($3>=500) {print $, ' is a common user. '} else {print $, "Isa system user or admin."}} ' /etc/passwd

# awk ' {if (nf>6) print NF, $} '/etc/inittab

usage: make conditional judgments on the fields in the entire row or row that awk obtains;

7.2 While Loop

syntax:while (condition) statement

while (condition) {statements}

The condition is true when the loop is made until the false exit;

Usage: Typically used for looping between fields in the current row;

# awk ' {i=1;while (I<=NF) {printf "%20s:%d\n", $i, Length ($i); i++}} '/etc/inittab

# awk ' {i=1;while (I<=NF) {if (length ($i) >5) {printf "%20s:%d\n", $i, Length ($i);} i++} '/etc/inittab

7.3 Do-while Cycle

syntax:do statement while (condition)

do {do-while-body} while (condition)

Meaning: At least one cycle body is executed;

7.4 for Loop

syntax:for (expr1; expr2; expr3) statement

for (EXPR1;EXPR2; expr3) {statements}

for (varaiable assignment; condition; iteration process) {For-body}

# awk ' {for (i=1;i<=nf;i++) {printf "%s:%d\n", $i, Length ($i)}} '/etc/inittab

The for Loop has a dedicated traversal array element in awk:

syntax:for (var in array) {For-body}

7.5 Switch

syntax:switch (expression) {case VALUE or/regexp/: statement; ...; DEFAULT:STATEMENTN}

7.6 Break and continue

Break [n]: exit current Loop

Continue: End this cycle ahead of time and go straight to the turn cycle

7.7 Next

End the processing of the bank in advance and proceed to the next line

# awk-f: ' {if ($3%2!=0) next;print $1,$3} '/etc/passwd

Eight, Array

associative array:array[index-expression]

Index-expression:

Any string can be used;

if an array element does not exist beforehand, when referenced,awk automatically creates the element and initializes its value to an empty string;

therefore, to determine whether an array exists for an element, use "indexin array";

a[mon]= "Monday"

Print A[mon]

to iterate through each element in the group, use:for (var in array) {for body}

Note:var iterates through each index of the array,print Array[var]

Example: Count the occurrences of each word in each row

# awk ' {for (i=1;i<=nf;i++) {count[$i]++}}end{for (J in count) {print j,count[j]}} ' Awk.txt

# Ss-tan | awk '!/^state/{state[$1]++}end{for (i in state) {print I,state[i]}} '

# Netstat-tan | awk '/^tcp/{state[$NF]++}end{for (i in state) {print I,state[i]}} '

For example: Statistics httpd access logs, the number of occurrences of each IP;

# awk ' {ip[$1]++}end{for (i in IP) {printi,ip[i]}} '/var/log/httpd/access_log

Nine, function

9.1 Built-in functions

Numerical Processing:

Rand (): Returns a random number between 0 and 1;

String processing:

Length ([s]): Returns the length of the specified string

Sub (R, S [, T]): finds the match in the T string in the pattern represented by R, substituting the string represented by the same s for the first occurrence ;

Sub (ab,ab,$0)

Gsub (R, S [, T]): finds the match in the T string in the pattern represented by R , replacing all occurrences with the string represented by S;

Split (S, a [, R]): cuts the string s with the R delimiter, and saves the result of the cut to a representation array;

# netstat-tan| awk '/^tcp/{len=split ($5,client, ":"); ip[client[len-1]]++}end{for (iin IP) {print i,ip[i]}} '

SUBSTR (S, I [, N]): takes a substring from the string represented by s, starting with I, taking n characters;

Functions of the time class:

Systime (): take time stamp;

Bit arithmetic functions:

and (V1,VA2):

9.2 Custom Functions

Functionf_name (P,Q)

{

...

}

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Linux basic awk simple to use