Mawk for Linux commands

Mawk for Linux commands

Pattern scanning and text processing language

Syntax:

Mawk [-F value] [-v var = value] [--] 'gram text' [file...]

Mawk [-F value] [-v var = value] [-f program-file] [--] [file...]

Description:

Awk is a text data processing language, and mawk is an interpreter for this language.

The awk program consists of the pattern {action} sequence and function definition. Input data is divided into records one by one based on RS (Record seperator, default = '\ n'). Each Record is compared with pattern. If it matches, the corresponding action is executed.

Option:

-F

Set field seperator and FS. Based on this value, record is divided into field

-F

Awk program file

-V var = value

Set program variables

--

Indicates that the mawk Command Option description is complete.

The following describes the AWK language.

1. Program Structure

As mentioned above, the awk program consists of the pattern {action} sequence or function definition.

Where, pattern can be

BEGIN

END

Expression

Expression, expression

If action is omitted, print is implicitly executed. If pattern is omitted, the matching is correct.

The statement is ended Based on the line break and semicolon.

Use # to annotate

Control Flow includes

If (expr) statement

If (expr) statement else statement

While (expr) statement

Do statement while (expr)

For (opt_expr; opt_expr) statement

For (var in array) statement

Continue

Break

2. Data Type, conversion and Comparison

There are two numeric and string types. All numbers are represented and computed using floating point numbers.

3. Regular Expression

Expr ~ /R/

The regular expression is enclosed by a slash. If expr is subject to this regular expression, it is true. Otherwise, it is false. "! ~" Is used for disobedience. .

/R/{action} and $0 ~ /R/{action} is equivalent.

4. Records and Fields

Read a row at a time, that is, a Records, and divide it into Fields according to FS. $0 indicates the entire Records, $1, $2 ,..., $ NF represents the corresponding Field. The built-in variable NF is the total number of Fields, and the Fields value higher than NF is set to "".

NR and FNR increase by 1 each time. The meaning is described later.

Assigning values to the preceding built-in variables will change the related variables.

5. Expressions and operators

Most operators are the same as those in C. Special operators include in (array membership ),~ (!~, Matching), $ (field ).

6. Array

Awk provides A one-dimensional array that uses A [1] or A ["1"] to access elements.

Delete array [expr] deletes the corresponding element.

If (I, j) in A) print A [I, j]

7. built-in Variables

CONVFMT: the internal conversion format from a numeric value to a string. The default value is "%. 6g"

ENVIRON: environment variable array, var = value is stored as ENVIRON [var] = value

FILENAME: name of the current input file

FNR: the number of the current record in the FILENAME File

FS: field separator, which can be a regular expression

NF: Total number of fields in the current record

NR: record number in all input streams

OFMT: Format of the output value. The default value is "%. 6g"

OFS: field Separator Used for output. The default value is space.

ORS: Specifies the record delimiter for output. The default Delimiter is a line break.

RS: The record delimiter used for input. The default value is line feed.

SUBSEP: used to build multiple array subscripts. The default value is "\ 034"

8. built-in functions

(1) string processing functions

Gsub (r, s, t) gsub (r, s)

Replace the character matching r in the t variable with s. If t is not specified, the hidden character is $0. Finally, the number of replicas is returned.

Index (s, t)

Returns the position where t appears for the first time in s. Otherwise, 0 is returned. The first character subscript of s is 1.

Length (s)

Returns the length of s.

Match (s, r)

Returns the longest matching subscript of r in s, and returns 0 if no matching exists.

Split (s, A, r) split (s,)

Divides s into A according to r, and returns the number of fields. if r is not set, use FS

Sprintf (format, expr-list)

Construct a string based on the format

Sub (r, s, t) sub (r, s)

Replace Once

Substr (s, I, n) substr (s, I)

Returns the substring of s from I to n.

Tolower (s)

Toupper (s)

(2) numeric processing functions

Atan2 (y, x)

Cos (x)

Exp (x)

Int (x)

Log (x)

Rand ()

Sin (x)

Sqrt ()

Srand (expr) srand ()

9. Input and Output

Print and printf are output.

Print

Output $0

Print expr1, expr2,..., exprn

Printf format, expr-list

The input is getline.

Getline

Read a row to $0

Getline <file

Read $0 from file

Getline var

Read the next record to var

Getline var <file

Read the next record from file to var

Command | getline

Execute command and read a record from the pipeline to $0

Command | getline var

Execute command and read a record from the pipeline to var

When getline encounters end-of-file, 0 is returned,-1 is returned, and 1 is returned.

Close (expr)

Close the file or pipe associated with expr

Fflush (expr)

System (expr) executes expr and returns the status

10. User-Defined Functions

Syntax:

Function name (args) {statements}

Can contain return opt_expr

11. Split strings, records, and files

12. Multi-line records processing

13. Program Execution

The BEGIN command is executed first.

Then process each record one by one based on the intermediate pattern {action}

You can use

Next

Exit opt_expr

Change the execution sequence of the program at the pattern level, read the next record directly upon next, and continue execution after in. exit immediately calls the actions corresponding to END, and opt_expr is the exit code.

Last run END