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This article mainly introduces how to use the awk command in Linux, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let Xiaobian take you to understand.

Awk is a programming language used to process text and data under linux/unix. The data can come from standard input (stdin), one or more files, or the output of other commands.

Awk programming language for text and data processing

It is added that awk supports advanced functions such as user-defined functions and dynamic regular expressions, and is a powerful programming tool under linux/unix. It is used on the command line, but more often as a script. Awk has many built-in functions, such as arrays, functions, etc., which is what it has in common with the C language. Flexibility is the biggest advantage of awk.

Awk command format and option syntax form

Awk [options] 'script' var=value file (s) awk [options]-f scriptfile var=value file (s) common command options

-F fs fs specifies the input delimiter, and fs can be a string or regular expression, such as-F:

-v var=value assigns a user-defined variable and passes the external variable to awk

-f scripfile reads awk commands from script files

The-m [fr] val sets an inherent limit on the vale value, the-mf option limits the maximum number of blocks allocated to the val, and the-mr option limits the maximum number of records. These two functions are extensions to the Bell lab version of awk and are not applicable in standard awk.

Awk schemas and operation awk scripts are made up of patterns and actions.

The pattern pattern can be any of the following:

/ regular expression /: an extended set that uses wildcards.

Relational expressions: operate using operators, which can be a comparison test of strings or numbers.

Pattern matching expressions: use the operators ~ (match) and! ~ (mismatch).

BEGIN statement blocks, pattern statement blocks, END sentence blocks: see how awk works

An action consists of one or more commands, functions, or expressions separated by line breaks or semicolons and in curly braces. The main parts are:

Variable or array assignment

Output command

Built-in function

Control flow statement

The basic structure of awk script awk 'BEGIN {print "start"} pattern {commands} END {print "end"}' file An awk script usually consists of three parts: BEGIN statement block, general statement block that can use pattern matching, and END statement block, which are optional. Any part can not appear in the script, which is usually enclosed in single or double quotes, for example:

How awk 'BEGIN {ionization +} END {print I}' filenameawk "BEGIN {ionization +} END {print I}" filenameawk works awk 'BEGIN {commands} pattern {commands} END {commands}' step 1: execute the statements in the BEGIN {commands} statement block

Step 2: read a line from the file or standard input (stdin), and then execute the pattern {commands} statement block, which scans the file line by line, repeating the process from the first line to the last line until all the files have been read.

Step 3: when reading to the end of the input stream, execute the END {commands} statement block.

The BEGIN statement block is executed before awk starts to read rows from the input stream, which is an optional statement block, such as variable initialization, printout table header, and so on, which can usually be written in the BEGIN statement block.

The END statement block is executed after awk has read all the lines from the input stream. For example, the summary of information such as printing the analysis results of all lines is done in the END statement block, which is also an optional statement block.

The general command in the pattern block is the most important part, and it is also optional. If no pattern statement block is provided, {print} is executed by default, that is, every row read is printed, and every line read by awk executes the statement block.

Example

Echo-e "A line 1\ nA line 2" | awk 'BEGIN {print "Start"} {print} END {print "End"}' Start A line 1 A line 2 End when using print with no parameters, it prints the current line, and when the parameters of print are separated by commas, a space is used as the delimiter. Double quotation marks are used as splicers in the print block of awk, for example:

Echo | awk'{var1= "v1"; var2= "v2"; var3= "v3"; print var1,var2,var3;}'v1 v2 v3 double quotation marks:

Echo | awk'{var1= "v1"; var2= "v2"; var3= "v3"; print var1 "=" var2 "=" var3;} 'v1=v2=v3 {} is similar to a loop body, iterating over each line in the file, usually variable initialization statements (such as: iS0) and statements for printing the file header are placed in the BEGIN statement block, and statements such as the printed results are placed in the END statement block.

Awk built-in variables (predefined variables) description: AP represents the first tool to support variables, [A] = awk, [N] = nawk, [P] = POSIXawk, [G] = gawk

* * $nails * the nth field of the current record. For example, n = 1 indicates the first field, and n = 2 indicates the second field. This variable contains the text content of the current line during execution. The number of [N] * * ARGC** command line arguments. [G] * * the location of the current file on the ARGIND** command line (starting at 0). [n] * * ARGV** contains an array of command line arguments. [G] * * CONVFMT** digital conversion format (default is% .6g). [P] * * ENVIRON** environment variable associative array. [n] * * description of the last system error in ERRNO**. [G] * * FIELDWIDTHS** field width list (separated by spacebar). [a] * * the name of the current input file for FILENAME**. [P] * * FNR** is the same as NR, but relative to the current file. [a] * * FS** field delimiter (default is any space). [G] * * IGNORECASE** if true, a match that ignores case is performed. [a] * * NF** represents the number of fields, which corresponds to the current number of fields during execution. [a] * * NR** represents the number of records, corresponding to the current line number during execution. [a] * * output format of OFMT** numbers (default is% .6g). [a] * * OFS** output field delimiter (default is a space). [a] * * ORS** outputs the record delimiter (the default is a newline character). [a] * * RS** record delimiter (default is a newline character). [n] * * RSTART** the first position of the string matched by the match function. [n] * * RLENGTH** the length of the string matched by the match function. [n] * * SUBSEP** array subscript delimiter (default is 34). Example

Echo-e "line1 f2 f3\ nline2 f4 f5\ nline3 f6 f7" | awk'{print "Line No:" NR ", No of fields:" $0 = "$0," $1 = "$1," $2 = "$2," $3 = "$3} 'Line No:1, No of fields:3 $0=line1 f2 f3 $1=line1 $2=f2 $3=f3 Line No:2, No of fields:3 $0=line2 f4 f5 $1=line2 $2=f4 $3=f5 Line No:3, No of fields:3 $0=line3 f6 f7 $1=line3 $2=f6 $3=f7 can print out the last paragraph of a line using print $NF. Use $(NF-1) to print the penultimate field, and so on:

Echo-e "line1 f2 f3\ nline2 f4 f5" | awk'{print $NF}'f3 f5 echo-e "line1 f2 f3\ nline2 f4" | awk'{print $(NF-1)}'f2 f4 prints the second and third fields of each line:

The number of lines in the awk'{print $2 recording 3} 'filename statistics file:

The above command awk 'END {print NR}' filename only uses the END statement block. When each line is read, awk updates the NR to the corresponding line number. When it reaches the last line, the value of the NR is the line number of the last line, so the NR in the END statement block is the number of lines in the file.

An example of the accumulation of the first field values in each line:

Seq 5 | awk 'BEGIN {sum=0; print "sum:"} {print $1 "+"; sum+=$1} END {print "equals"; print sum}' sum: 1 + 2 + 3 + 4 + 5 + equals 15 external variable values are passed to awk with the-v option, external values (not from stdin) can be passed to awk:

VAR=10000 echo | awk-v VARIABLE=$VAR'{print VARIABLE} 'another way to pass external variables:

Var1= "aaa" var2= "bbb" echo | awk'{print v1je v2} 'v1=$var1 v2=$var2 when input comes from a file:

In the above method of awk'{print v1 direction v2} 'v1=$var1 v2=$var2 filename, variables are separated by spaces as command-line arguments to awk followed by blocks of BEGIN, {}, and END statements.

Lookup process pid netstat-antup | grep 7770 | awk'{print $NF NR}'| awk'{print $1} 'awk operation and judgment is one of the characteristics of a programming language. Awk supports a variety of operations, which are basically the same as those provided by C language. Awk also provides a series of built-in operation functions (such as log, sqr, cos, sin, etc.) and functions for manipulating (calculating) strings (such as length, substr, and so on). The reference of these functions greatly improves the operation function of awk. As part of the conditional transfer instruction, relationship judgment is a function of every programming language, and awk is no exception. Awk allows a variety of tests, as well as pattern matching expressions (matching) and! (mismatching). As an extension of testing, awk also supports logical operators.

The arithmetic operator describes +-add, subtract * / & multiply, divide and find the remainder + -! Unary addition, subtraction, and logic are not ^ * exponentiated + +-increase or decrease, as prefixes or suffixes:

Awk 'BEGIN {a = "b"; print axioms;}' 02 Note: all operands are used as arithmetic operators, operands are automatically converted to numeric values, and all non-numeric values become 0

Assignment operator description = + =-= * / =% = ^ = * * = assignment statement example:

Description of other similar logic operators\ |\ | logic or & & logic and examples:

Awk 'BEGIN {a regular 1 & & b5 & b5 | | b regular operator description ~! ~ matches regular expressions and mismatches regular expressions:

Awk 'BEGIN {a = "100testa"; if (a ~ / ^ 100 ok /) {print "ok";}}' ok relational operator description > =! = relational operator example:

Awk 'BEGIN {axi11bot if (a > = 9) {print "ok";}}' ok Note: >

Other operator operators describe whether a key exists in the $field referencing a space string concatenation?: C conditional expression in array:

Awk 'BEGIN {a = "b"; print asides = "b"? "ok": "err";}' ok awk 'BEGIN {a = "b"; arr [0] = "b"; arr [1] = "c"; print (an in arr);}' 0 awk 'BEGIN {a = "b"; arr [0] = "b"; arr ["b"] = "c"; print (an in arr);}' 1 arithmetic priority list! The higher the level, the higher the priority.

Awk Advanced I / O reads the next record awk uses the next statement: match line by line in a loop. If you encounter next, the current line will be skipped and the following statement will be ignored directly. And match the next line. The next statement is generally used for multiline merging:

Cat text.txt a b c d e awk 'NR%2==1 {next} {print NR,$0;}' text.txt 2 b 4d skips the current line when the record line number is divided by 2 or more than 1. The following print NR,$0 will not be executed either. At the beginning of the next line, the program starts to judge the NR% 2 value. When the record line number is: 2, the following statement block will be executed: 'print NR,$0'

The analysis found that the line containing "web" needs to be skipped, and then the content needs to be merged into one line with the following line:

Cat text.txt web01 [192.168.2.100] httpd ok tomcat ok sendmail ok web02 [192.168.2.101] httpd ok postfix ok web03 [192.168.2.102] mysqld ok httpd ok 0 awk'/ ^ web/ } 'text.txt web01 [192.168.2.100]: httpd ok web01 [192.168.2.100]: tomcat ok web01 [192.168.2.100]: sendmail ok web02 [192.168.2.101]: httpd ok web02 [192.168.2.101]: postfix ok web03 [192.168.2.102]: mysqld Ok web03 [192.168.2.102]: httpd ok simply reads a record awk getline usage: output redirection requires the getline function. Getline gets input from standard input, pipes, or other input files other than the one currently being processed. It is responsible for getting the contents of the next line from the input and assigning values to built-in variables such as NF,NR and FNR. If you get a record, the getline function returns 1, 0 if you reach the end of the file, and-1 if there is an error, such as a failure to open the file.

Getline syntax: getline var, the variable var contains the contents of a specific line.

Awk getline as a whole, usage instructions:

When there is no redirector left or right: getline acts on the current file and reads the variable var or $0 (no variable) followed by the first line of the current file. It should be noted that because awk has already read one line before processing getline, the return result from getline is interlaced.

When there is a redirect character around it: getline acts on the directed input file, because the file has just been opened and is not read into a line by awk, but by getline, then getline returns the first line of the file, not an interlaced one.

Example:

Execute the date command of linux and pipe it to getline, then assign the output to the custom variable out and print it:

Awk 'BEGIN {"date" | getline out; print out}' test executes the date command of shell and outputs it to getline through the pipe, then getline reads from the pipe and assigns the input to the out,split function to convert the variable out into an array mon, and then prints the second element of the array mon:

Awk 'BEGIN {"date" | getline out; split (out,mon); print mon [2]}' test command the output of ls is passed to geline as input, and the loop causes getline to read a line from the output of ls and print it to the screen. There is no input file here, because the BEGIN block executes before opening the input file, so you can ignore the input file.

Awk 'BEGIN {while ("ls" | getline) print}' close the file awk allows you to close an input or output file in the program by using the close statement of awk.

Close ("filename") filename can be a file opened by getline, or it can be stdin, a variable containing the file name, or the exact command used by getline. Or an output file, which can be stdout, a variable containing the file name, or an exact command to use the pipe.

Output to a file awk allows you to output the results to a file as follows:

Echo | awk'{printf ("hello wordwords") > "datafile"}'# or echo | awk'{printf ("hello wordwords") > > "datafile"} 'sets the field delimiter. The default field delimiter is a space. You can specify a delimiter explicitly using-F "delimiter":

Awk-F:'{print $NF}'/ etc/passwd # or awk 'BEGIN {FS= ":"} {print $NF}' / etc/passwd in the BEGIN statement block, you can set the delimiter of the output field with the OFS= "delimiter".

Process control statements allow the use of break,continue statements to control the direction of the process in linux awk's while, do-while, and for statements, as well as statements such as exit to exit. Break interrupts the currently executing loop and jumps out of the loop to execute the next statement. If is the process selection usage. In awk, process control statements, syntax structures, and c language types. With these statements, in fact, many shell programs can be handed over to awk, and the performance is very fast. The following is the usage of each statement.

Conditional judgment statement if (expression) statement 1 else statement 2 format can be multiple statements, in order to facilitate judgment and reading, it is best to enclose multiple statements in {}. The awk branching structure allows nesting in the following format:

If (expression) {statement 1} else if (expression) {statement 2} else {statement 3} example:

Awk 'BEGIN {test=100; if (test > 90) {print "very good";} else if (test > 60) {print "good";} else {print "no pass";}}' very good is available after each command statement; ends with a semicolon.

Loop statement # while statement while (expression) {statement} example:

Awk 'BEGIN {test=100;total=0;while (i# for loop for loop has two formats: format 1:for (variable in array) {statement} example: awk' BEGIN {for (k in ENVIRON) {print k "=" ENVIRON [k];}} 'TERM=linux G_BROKEN_FILENAMES=1 SHLVL=1 pwd=/root/text. Logname=root HOME=/root SSH_CLIENT=192.168.1.21 53087 22 Note: ENVIRON is an awk constant and a subtypical array. Format 2: for (variable; condition; expression) {statement} example: awk 'BEGIN {total=0; for (ido loop do {statement} while) example: awk' BEGIN {total=0; iexpression 0; do {total+=i;i++;} while (I other statements break causes the program loop to exit when the break statement is used in while or for statements.

Continue causes the program loop to move to the next iteration when the continue statement is used for the while or for statement.

Next can cause the next input line to be read and returned to the top of the script. This avoids performing other operations on the current input line.

The exit statement exits the main input loop and transfers control to END, if END exists. If no END rules are defined, or if the exit statement is applied in the END, the execution of the script is terminated.

Array application array is the soul of awk, and the most important thing in dealing with text is its array processing. Because the array index (subscript) can be numbers and strings, an array in awk is called an associative array (associative arrays). Arrays in awk do not need to be declared in advance, nor do they have to declare size. Array elements are initialized with a 0 or an empty string, depending on the context.

The defined number of the array is indexed (subscript):

Array [1] = "sun" Array [2] = "kai" string to do array index (subscript):

Array ["first"] = "www" Array "[last"] = "name" Array ["birth"] = "1987" in use print Array [1] will print out sun; using print Array [2] will print kai; using print ["birth"] will get 1987.

Read the value of the array

{for (item in array) {print array [item]};} # the order of output is random {for (item1witi array correlation function to get the array length: awk 'BEGIN {info= "it is a test"; lens=split (info,tA, "); print length (tA), lens;}' 4 4length returns the string and the array length, split splits the string into the array, and also returns the split to get the array length. Awk 'BEGIN {info= "it is a test"; split (info,tA, "); print asort (tA);}' 4asort sorts the array and returns the array length. Output array contents (unordered, ordered output): awk 'BEGIN {info= "it is a test"; split (info,tA, ""); for (k in tA) {print kmint A [k];}}' 4 test 1 it 2 is 3 afor... In output, because the array is associative and unordered by default. So through for... In gets an array that is unordered. If you need to get an ordered array, you need to get it through the subscript. Awk 'BEGIN {info= "it is a test"; tlen=split (info,tA, "); note: the array subscript starts at 1, which is different from the C array. Judging the existence of keys and deleting keys: # incorrect judgment methods: awk 'BEGIN {tB ["a"] = "A1"; tB ["b"] = "b1"; if (tB ["c"]! = "1") {print "no found";}; for (k in tB) {print kline TB [k] There is a strange problem above no found an A1 b b1 c. TB ["c"] is not defined, but when looping, it is found that the key value already exists and its value is empty. It should be noted that the awk array is an associative array, and as long as its key is referenced through the array, a modification sequence will be created automatically. # correct judgment method: awk 'BEGIN {tB ["a"] = "A1"; tB ["b"] = "b1"; if ("c" in tB) {print "ok";}; for (k in tB) {print k b1if TB [k];}} an A1 b b1if (key in array) uses this method to determine whether the array contains key key. # delete key value: awk 'BEGIN {tB ["a"] = "A1"; tB ["b"] = "b1"; delete tB ["a"]; for (k in tB) {print k b1delete array TB [k];}' b b1delete array [key] can be deleted, corresponding to the sequence value of the array key. Two-dimensional and multidimensional arrays multidimensional arrays using awk are essentially one-dimensional arrays. More precisely, awk does not support multidimensional arrays in storage. Awk provides access to logically simulate two-dimensional arrays. For example, access such as array [2pr 4] = 1 is allowed. Awk uses a special string SUBSEP ("34) as the split field. In the above example, the key value stored in the associative array array is actually 2 '344. Similar to the member test of an one-dimensional array, a multi-dimensional array can use syntax such as if ((iMagnej) in array), but the subscript must be placed in parentheses. Similar to the iterative access of one-dimensional arrays, multi-dimensional arrays use syntax such as for (item in array) to traverse the array. Unlike an one-dimensional array, a multi-dimensional array must use the split () function to access individual subscript components. Awk 'BEGIN {for (iMag1bot I) can get the contents of the array through the reference of array [kjournal K2]. Another method: awk 'BEGIN {for built-in function awk built-in function, mainly divided into the following three kinds of similar: arithmetic function, string function, other general function, time function. The arithmetic function format describes that atan2 (y, x) returns the inverse tangent of y _ Unix. Cos (x) returns the cosine of x; x is radians. Sin (x) returns the sine of x; x is the Radian. Exp (x) returns an x power function. Log (x) returns the natural logarithm of x. Sqrt (x) returns the square root of x. Int (x) returns the truncated value of x to an integer. Rand () returns any number n, where 0srand ([expr]) sets the seed value of the rand function to the value of the Expr parameter, or uses the time of day if the Expr parameter is omitted. Returns the previous seed value. Examples are as follows:

Awk 'BEGIN {OFMT= ".3f"; fs=sin (1); fe=exp (10); fl=log (10); fi=int (3.1415); print fs,fe,fl,fi;}' 0.841 22026.466 2.303 3OFMT sets the output data format to retain 3 decimal places.

Get a random number:

Awk 'BEGIN {srand (); fr=int (100*rand ()); print fr;}' 78 awk 'BEGIN {srand (); fr=int (100*rand ()); print fr;}' 31 awk 'BEGIN {srand (); fr=int (100*rand ()); print fr;}' 41 string function format description gsub (Ere, Repl, [In]) except that all specific values of the regular expression are replaced, it executes exactly the same as the sub function. Sub (Ere, Repl, [In]) replaces the first concrete value of the extended regular expression specified by the Repl parameter in the string specified by the In parameter with the string specified by the Ere parameter. The sub function returns the number of replacements. The & (and symbols) that appear in the string specified by the Repl parameter are replaced by the string specified by the In parameter that matches the specified extended regular expression of the Ere parameter. If the In parameter is not specified, the default value is the entire record ($0 record variable). Index (String1, String2) returns the position in the string specified by the String1 parameter (where the parameter specified by String2 appears), numbering starting at 1. Returns 0 if the String2 parameter does not appear in the String1 parameter. Length [(String)] returns the length (in character form) of the string specified by the String parameter. If no String parameter is given, the length of the entire record ($0 record variable) is returned. Blength [(String)] returns the length, in bytes, of the string specified by the String parameter. If no String parameter is given, the length of the entire record ($0 record variable) is returned. Substr (String, M, [N]) returns a substring with the number of characters specified by the N parameter. The substring is taken from the string specified by the String parameter, whose characters begin at the position specified by the M parameter. The M parameter is specified to take the first character in the String parameter as the number 1. If the N parameter is not specified, the length of the substring will be the length from the position specified by the M parameter to the end of the String parameter. Match (String, Ere) returns the position (in character form) in the string specified by the String parameter (where the extended regular expression specified by the Ere parameter appears), numbering from 1, or 0 (zero) if the Ere parameter does not appear. The RSTART special variable is set to the return value. The RLENGTH special variable is set to the length of the matching string, or to-1 (minus one) if no match is found. Split (String, A, [Ere]) divides the parameters specified by the String parameter into array elements A [1], A [2],. . , A [n] and returns the value of the n variable. This separation can be done through the extended regular expression specified by the Ere parameter, or by the current field delimiter (FS special variable) (if no Ere parameter is given). Unless the context indicates that a particular element should also have a numeric value, elements in the An array are created with string values. Tolower (String) returns the string specified by the String parameter, and each uppercase character in the string is changed to lowercase. Uppercase and lowercase mappings are defined by the LC_CTYPE category of the current locale. Toupper (String) returns the string specified by the String parameter, and each lowercase character in the string is changed to uppercase. Uppercase and lowercase mappings are defined by the LC_CTYPE category of the current locale. Sprintf (Format, Expr, Expr,. . . Formats the expression specified by the Format parameter according to the printf subroutine format string specified by the Expr parameter and returns the last generated string. Note: Ere can be regular expressions.

Gsub,sub usage

Awk 'BEGIN {info= "this is a test2010test!"; gsub (/ [0-9] + /, "!", info); print info}' this is a testing! Find the regular expression in info, / [0-9] + / replace it with "", and the value after replacement is assigned to info without a value of info. The default is $0.

Find string (used by index)

Awk 'BEGIN {info= "this is a test2010test!"; print index (info, "test")? "ok": "no found";}' ok not found, return 0

Regular expression matching lookup (used by match)

Awk 'BEGIN {info= "this is a test2010test!"; print match (info,/ [0-9] + /)? "ok": "no found";}' ok intercept string (used by substr)

[wangsl@centos5 ~] $awk 'BEGIN {info= "this is a test2010test!"; print substr (info,4,10);}' s is a tes starts with the fourth character and intercepts 10 length strings

String segmentation (used by split)

Awk 'BEGIN {info= "this is a test"; split (info,tA, "); print length (tA); for (k in tA) {print k this tA [k];}}' 44 test 1 this 2 is 3a split info, dynamically create an array tA, which is interesting here, awk for... An in loop is a disordered loop. Not from the array subscript 1... N, so you need to pay attention when using it.

Format string output (used by sprintf)

Format string format:

The formatting string consists of two parts: one is normal characters, which will be output as is; the other is formatting specified characters, starting with "%", followed by one or more specified characters to determine the format of the output content.

Format description format description% d decimal unsigned integer% u unsigned integer% f floating point% s string% c value of single character% p pointer% e floating point% x% X unsigned integer in hexadecimal% o unsigned integer in octal% g automatically choose the appropriate representation awk 'BEGIN {n1x 124.113 Printf ("% .2f,% .2u,% .2g,% XMagi% on", n1Magi n2Magi n3PowerN1); 18446744073709551615 printf (Expression) uses the same Expression parameter with string values to close files or pipes opened by print or printf statements or by calling getline functions. Returns 0 if the file or pipe is successfully closed; otherwise, a non-zero value is returned. If you plan to write a file and read it later in the same program, the close statement is required. System (command) executes the command specified by the Command parameter and returns the exit status. Is equivalent to the system subroutine. Expression\ | getline [Variable] reads an input record from the output from the command specified by the Expression parameter and assigns the value of the record to the variable specified by the Variable parameter. If a stream with the value of the Expression parameter as its command name is not currently open, the stream is created. The created stream is equivalent to calling the popen subroutine, where the Command parameter takes the value of the Expression parameter and the Mode parameter is set to a value of r. As long as the stream remains open and the Expression parameter evaluates the same string, another record is read for each subsequent call to the getline function. If the Variable parameter is not specified, the $0 record variable and the NF special variable are set to the record read from the stream. Getline [Variable] reads the next record entered from the file specified by the Expression parameter and sets the variable specified by the Variable parameter to the value of that record. As long as the stream remains open and the Expression parameter evaluates the same string, another record is read for each subsequent call to the getline function. If the Variable parameter is not specified, the $0 record variable and the NF special variable are set to the record read from the stream. Getline [Variable] sets the variable specified by the Variable parameter to the next input record read from the current input file. If the Variable parameter is not specified, the $0 record variable is set to the value of that record, and the NF, NR, and FNR special variables are also set. Open an external file (close usage)

Awk 'BEGIN {while ("cat / etc/passwd" | getline) {print $0;}; close ("/ etc/passwd");}' root:x:0:0:root:/root:/bin/bash bin:x:1:1:bin:/bin:/sbin/nologin daemon:x:2:2:daemon:/sbin:/sbin/nologin reads external files line by line (how to use getline)

Awk 'BEGIN {while (getline awk' BEGIN {print "Enter your name:"; getline name;print name;} 'Enter your name: chengmo chengmo calls external application (system usage) awk' BEGIN {b=system ("ls-al"); print b;} 'total 42092 drwxr-xr-x 14 chengmo chengmo 4096 09-30 17:47. Drwxr-xr-x 95 root root 4096 10-08 14:01... b returns a value that is the result of the execution. Time function format description function name description mktime (YYYY MM dd HH MM ss [DST]) generates time format strftime ([format [, timestamp]]) to format the time output, and converts the timestamp into a time string format, as shown in the following table. Systime () gets the timestamp and returns the specified time in seconds from January 1, 1970 to the current time (excluding leap years) (used by mktime)

Awk 'BEGIN {tstamp=mktime ("2001 01 01 12 12 12"); print strftime ("% c", tstamp);}' 2001 01 01 Monday 12:12:12 awk 'BEGIN {tstamp1=mktime ("2001 01 12 12 12"); tstamp2=mktime ("2001 02 01 00"); print tstamp2-tstamp1;}' 2634468 calculates the time difference between two time periods and introduces the use of strftime

Awk 'BEGIN {tstamp1=mktime ("2001 01 01 12 12"); tstamp2=systime (); print tstamp2-tstamp1;}' 308201392strftime date and time format specifier

Format description of the day of the week (Sun)% A full abbreviation (Sunday)% b month name (Oct)% B month name (October)% c local date and time% d decimal date% D date 08and20and99% e date If only one person would fill in a space% H to represent hours in 24-hour format in decimal, I in decimal to represent hours in 12-hour format, j in decimal representation of month% M in decimal representation of days of the year from January 1 onwards, minute% p12 hour representation (AM/PM)% S decimal representation in seconds% U decimal representation of the week of the year (star) The day of the week as the beginning of the week)% w decimal day (Sunday is 0)% W decimal day of the year (Monday as the beginning of the week)% x reset local date (08pm 20pm 99)% X reset local time (12:00:00)% y double digit year (99)% Y current month% sign ( Thank you for reading this article carefully I hope the article "how to use awk commands in Linux" shared by the editor will be helpful to you. At the same time, I also hope that you will support us and pay attention to the industry information channel. More related knowledge is waiting for you to learn!

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