awk Usage II

3. The printf command of awk

Format: printf format, item1 item2 ...

Points:

(1) to specify format;

(2) Output will not be automatically wrapped, if you need to change the line must be given \ n;

(3) format is used to specify its output format for each subsequent item;

(4) The format indicator is a% beginning, followed by a character.

Characters commonly used in format:

%c: ASCII code for displaying characters

%d,%i: decimal integer;

%e,%e: Scientific counting method;

%f: Displays floating-point numbers;

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

%s: Display string;

%u: Displays unsigned integers;

Percent: show% itself.

Common modifiers in format:

#: Display width;

-: left-aligned;

+: Display the symbol of the value;

. #: Value precision.

Example 1: The user name and shell information for the first 10 records in the/etc/passwd file with a fixed width of 20 output:

650) this.width=650; "title=" 1451027583534543.jpg "alt=" 1.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20151225/1451027583534543.jpg "/>

The partial meaning of the above example is that two fields are displayed with a width of 20 characters, and a newline character is the Terminator for each line.

Example 2: Display the user name in the previous example as left-justified:

650) this.width=650; "title=" 1451027891544274.jpg "alt=" 2.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20151225/1451027891544274.jpg "/>

Example 3:3.14159 takes 2 decimal places to display:

650) this.width=650; "title=" 1451028126980072.jpg "alt=" 3.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20151225/1451028126980072.jpg "/>

4. Awk's operator

Arithmetic operators:

X+y: Plus

X-y: Minus

X*y: Multiply

X/y: except

x** (^) y: exponentiation

X%y: Take the mold

-X: Negative value

+x: Convert to Numeric

String operators:

Connection: No need to sign, directly put two strings together on it;

Assignment operators:

X=y: Assigns the value of Y to X;

X+=y: Assigns the result of the x+y to X;

X-=y: The X-y result is assigned to X.

X/=y: The result of dividing x by Y is assigned to X;

X%=y: Assigns the result of X and y to x;

X^=y or x**=y: assigns x to the result of the Y-order to X;

X + +: Assigns the result of the x+1 to X.

x--: Assigns the result of the x+1 to X;

Note: If the mode itself is the = sign, write as/=/

Comparison operators:

X<y: True if x is less than y;

X<=y: True if X is less than or equal to Y;

X>y: True if x is greater than Y;

X>=y: True if x is greater than or equal to Y;

X==y: True if x equals y;

X~y: Pattern matching, x can be matched to true by Y mode.

Logical operators:

X&&y: Executes y if x is true;

x| | Y: Executes y if X is false.

Conditional expression:

Selector? if-ture-expression:if-false-expression

Selector: Conditions

If-ture-expression: This expression is executed if true

: if-false-expression: Otherwise execute this expression

Example 4: Judging that the UID in the/etc/passwd file is greater than 500 is displayed as "Common user", otherwise it will appear as "Admin user":

650) this.width=650; "title=" 1451031871504107.jpg "alt=" 4.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20151225/1451031871504107.jpg "/>

5. Mode

(1) Regular expressions

Format:/pattern/

Example 5: Displays only the lines in the/etc/passwd file that are rooted:

650) this.width=650; "title=" 1451032329498004.jpg "alt=" 5.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20151225/1451032329498004.jpg "/>

(2) expression

The majority of the comparison expressions, which result in a non-0 or non-empty string, satisfy the condition, and awk only handles rows that satisfy the condition.

Example 6: Only rows with uid greater than or equal to 500 are displayed:

650) this.width=650; "title=" 1451032503683123.jpg "alt=" 6.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20151225/1451032503683123.jpg "/>

(3) Special mode

BEGIN: Executes once before the program of the awk command is run;

END: Executes once after the program of the awk command is run.

Example 6: Displays the user name of the line in the/etc/passwd file that starts with root in the person, UID, shell information, displays the fields separated by commas, and prints "the end" after the result is output.

650) this.width=650; "title=" 1451033850450162.jpg "alt=" 7.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20151225/1451033850450162.jpg "/>

(5) Empty mode

Used to match any row.

650) this.width=650; "title=" 1451034170926634.jpg "alt=" 8.jpg "src=" http://www.178linux.com/ueditor/php/upload/ Image/20151225/1451034170926634.jpg "/>

awk Usage II