The awk of Linux

One: awk is the report generator

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awk field: awk cuts the contents of the row into each field by delimiter on each line of the document.

$: Represents the entire row.

$ ... $N: represents each field separated by a separator.

II: awk BASIC syntax

Basic syntax:awk [Options] ' program ' File file ...

awk [options] ' pattern{action} ' file File ...

input option: -f Specifies the separator option.

awk - F: ' {print $, $7} '/etc/passwd #指定以冒号作为字段分割符.

Output of the Pattern:awk

Print item1, Item2, .....

Key points:

(1) Each item is separated by commas, and

the output is separated by an output delimiter, and

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

(3) Print after item if omitted, the equivalent of print to output the entire string of content; to output whitespace later, use pirnt "" (Output in awk

Substring to use double quotes);

awk variables: Built-in variables, custom variables

built-in variables: field separators at input (begin before awk's built-in variables)

fs:field seperator, field delimiter at input

# awk ' begin{fs= ': "}{print $1,$7} '/etc/passwd #内置变量的引用要用到双引号

Rs:record seperator, enter line delimiter

# awk ' begin{rs= ': "}{print} '/etc/passwd #会把冒号分开的内容当作每一行来处理

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ofs:output field seperator, Fields delimiter at output

# awk ' BEGIN{fs= ': " ; Ofs= ":"}{print $1,$7} '/etc/passwd #语句与语句之间要用分号分割 (red section)

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ors:outpput row seperator, line delimiter at output

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nf:numbers of field, number of fields #取最后一个字段还可用 $NF

nr:numbers of Record, number of rows if followed by multiple files, then all files are counted together;

# awk ' begin{fs= ': "; ofs=": "}{print NR $1,$7} '/etc/passwd/etc/group

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FNR: Number of rows; count each file separately ;

# awk ' begin{fs= ': "; ofs=": "}{print FNR $1,$7} '/etc/passwd

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ARGV: An array that holds the character of the command itself, awk ' {print $} ' 1.txt 2.txt, meaning argv[0] saves awk,

# awk ' Begin{print argv[0], argv[1],argv[2],ARGC} '/etc/passwd/etc/group

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ARGC: Save the number of arguments in the awk command

Custom variable: Field delimiter at input (use begin before Awk's built-in variable )

   -v var_name=value   variable name distinguishing character case

  (1) variable can be defined in program;

  (2) can customize variables via the-v option on the command line;

 # awk ' begin{a= ' Hello awk '}{print A} '/etc/passwd

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#awk ' begin{a= ' Hello awk ';p rint A} ' #可以不跟文件 output Hello awk directly

#awk-v a= "Hello awk" ' Begin{print A} ' #直接输出hello awk

Awk's printf command

Use format for commands: printf format, item1, item2,...

Points:

(1) to specify format;

(2) will not be automatically wrapped, if you want to change the line, you need to give \ n

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

The format indicator is preceded by%, followed by a character:

%c: The ASCII code that displays the characters;

%d,%i: decimal integer;

%e,%e: The scientific counting method shows the numerical value;

%f: Displays floating-point numbers;

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

%s: Display string;

%u: Displays unsigned integers;

Percent: show% itself;

Modifier:

#: Display width

-: Align Left

+: Display symbols for numeric values

. #: Value Accuracy

# awk-f: ' {printf '%15s%-15s\n ', $1,$7} '/etc/passwd

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# awk ' BEGIN {printf '%f\n ', 3.1415} ' #显示7个字节

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# awk ' BEGIN {printf '%f\n ', 3.1415926} ' #总位数超过8位, rounding after decimal point

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# awk ' BEGIN {printf '%15.2f\n ', 3.1415926} ' #15.2 indicates that the whole is 15 bits wide plus two digits after the decimal point

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awk output Redirection

Print Items > Output-file

Print Items >> output-file

Print Items | Command

Special File Descriptor:

/dev/stdin: Standard input

/dev/stdout: Standard Output

/dev/stderr: Error Output

Awk's operator

Arithmetic operators:

X+y

X-y

X*y

X/Y

X**y, X^y

X%y

-X: Negative value

+x: Convert to Numeric

String operators: Connecting

Assignment operators:

=

+=

-=

*=

/=

%=

^=

**=

++

--

If the pattern itself is the = sign, write as/=/

Comparison operators:

<

<=

>

>=

==

!=

~: Pattern matching, the left string can be matched to the right pattern to true, otherwise false;

!~:

Logical operators:

&&: With

|| : OR

Conditional expression:

Selector?if-true-expression:if-false-expression

# awk-f: ' {$3>=500?utype= ' common user ': utype= ' admin or System user ';p rint $, ' is ', utype} '/etc/passwd

Function call:

Function_name (ARGU1,ARGU2)

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The awk of Linux