[Awk Introduction:]
Awk can obtain part of the content from a text, or typeset the text so that it can be output in a certain format.
[Awk workflow:]
Awk will upload a row of file content to the memory and segment the content in this line (separated by spaces or tabs by default, $1, $2, $3 ...). and then read the second line to the memory... format: awk '{/pattern/command1; command2 ;...} 'File # execute the command in the matching mode, for example, who | awk '{print $1}' # print the first part of the segment, $1 is the first part, $0 indicates all content in a row.
[Awk parameter description:]
-F re: Allows awk to change its field separator. -V defines variables and transmits variables from shell to awk, such as-vDATE = $ DATE, that is, the $ DATE variable value in shell is passed to the awk variable DATE.
-F progfile: allows the awk to call and execute the progfile program file. Of course, the progfile must be a program file that complies with the awk syntax.
[Awk built-in variables:]
Number of ARGC command line parameters
ARGV command line parameter Array
Argind argv flag of the currently processed file awk '{if (ARGIND = 1) {print $1} if (ARGIND = 2) {print $2} 'aaa.txt bbb.txt # first scans the aaa file and then the bbb File
Number of records read by NR awk 'nr = 1, NR = 5 {print} 'aaa.txt # displays 1 to 5 rows of aaa.txt files
FNR current file records awk 'nr = FNR {print "a"} NR> FNR {print "B"} 'a.txt B .txt # input file a.txt and B .txt, when scanning a.txt, there must be NR = FNR; # After scanning B .txt, FNR starts to count from 1, while NRIS connected to the number of a.txt rows, so NR> FNR
FS input field separator (default: space :), equivalent to-F option awk-F': ''{print $1} 'ccc.txt # input file: As the delimiter
OFS output field separator (default: space :) # when outputting; split ① cat ccc.txt as follows:
② Awk-F': ''BEGIN {OFS ="; "} {print $1, $2, $3} 'ccc.txt
③ The output result is as follows:
1; 2; 3
4; 5; 6
Number of parts in the current NF record awk-F': ''{print NF} 'ccc.txt
The RS input record delimiter. The default value is "\ n". By default, awk regards a row as a record. If RS is set, awk splits the record according to RS ① cat ccc.txt: hello world; I want to go mongoming tomorrow; hiahia
② Run awk 'in in {RS = ";"} {print} 'ccc.txt
③ The result is as follows: hello world
I want to go mongoming tomorrow
Hiahia
ORS output record delimiter, which is a line break by default and controls the output symbols after each print statement
Awk 'in in {FS = "\ n"; RS = ""; ORS = ";"} {print NF} 'ddd.txt
[Awk built-in functions:]
Blength [([s])] calculates the string length in bytes)
Length [([s])] calculates the string length (character)
Rand () to generate a random number
Srand ([expr]) set rand () seed
Converts an int (x) string to an integer.
Substr (s, m [, n ])
Index (s, t) locates the first occurrence position of the t string in string s.
Match (s, ere) matches regular ere in string s. match modifies the RSTART and RLENGTH variables.
Split (s, a [, fs]) Splits strings into arrays.
Sub (ere, repl [, in]) string replacement
Gsub is the same as above
Sprintf (fmt, expr,...) spell string
System (cmd): Execute cmd in shell.
Toupper (s) string converted to uppercase
Tolower (s) string to lowercase
[Awk usage example:]
1. -F indicates what is used as the separator awk-F: '{print $1}' ccc.txt # With: As the separator, print the first line of the string awk-F in the ccc.txt file: '{print $1, $2}' ccc.txt # print the first and second strings. If you write $1 $2 in this way, the printed content will be connected together.
2./pattern match awk-F: '/A/{print $1}' ccc.txt # Use: As the separator to print the first string containing A in the ccc.txt File
3. ^ indicates the start of awk-F: '/^ A/{print $1}' ccc.txt # Use: As the separator to print the first string starting with A in the ccc.txt File
4 .~ Awk-F: '$4 ~ /A/{print $1} 'ccc.txt # Use: As the separator to print the string containing A in the fourth section of the ccc.txt File
5. before reading the first line into the memory, awk can perform other operations in the BEGIN format: awk 'in in {command}/pattern/{command1; command2 ;...} 'File
Awk 'in in {FS = ":"} $1 ~ /A/{print $1} 'ccc.txt # before reading the ccc.txt file, first run the command in BEGIN and set: As the delimiter awk 'begin {FS = ":"; OFS = "-"} $1 ~ /A/{print $1, $2} 'ccc.txt # Separate the output Separators-
6. after all the rows are processed, you can perform some operations first, using the END format: awk 'in in {command}/pattern/{command1; command2 ;...} END {command} 'file
7. Use NF who | awk '{print NF}' to count the number of segments after each row }'
8. Get awk to process the file content. In the source file, use NR awk-F: '/^ A/{print NR}' ccc.txt # To obtain the number of lines starting with A in ccc.txt.
9. custom variable awk 'in in {a = 0}/tb/{a ++} END {print a} 'ccc.txt # define a variable before circulating the ccc.txt file. The initial value is 0; then, loop through each row, and Add 1 to a for each row that contains tb until the value of a is printed.
