Awk command operation details

1. Record and Field

   Awk reads a record from the file at a time and stores the record in the field variable $0. Records are separated into fields. The function is stored in $1, $2,... $ NF. (space or indicator Delimiter is used by default ). The built-in parameter NF is the number of recorded fields.

   Outputs 1st, 2nd, 3rd, and 4th fields of the demo.txt file.
   

   Awk '{print $1, $2, $3, $4}' demo.txt

   Parse outputs the entire line of the demo.txt File
   

   Awk '{print $0}' demo.txt

   The number of fields in this row in demo.txt output by workers.

   Awk '{print NF}' demo.txt

   The number of fields in this row in demo.txt output by workers.

   Awk '{print $ NF}' demo.txt

2. Field Separator

   By default, awk reads data using spaces or indicator characters as separators. However, you can use the-f or FS (field separator) variable to change more characters.

   Awk-F: '{print $1}'/etc/passwd
   Awk 'in in {FS = ":"} {print $1} '/etc/passwd

   Echo 'Hello The: World ,! '| Awk' begin {FS = "[:,]"} {print $1, $2, $3, $4 }'
   

3. Built-in variable description
   

   Number of argc command line parameters

   Filename name of the current input file
   

   FNR indicates the number of the current record of the current input document, especially when multiple input documents exist.

   Current input record number of the NR input stream

   Number of fields recorded by NF

   FS Field Separator

   Specifies the delimiter of the output field of OFS. The default Delimiter is space.

   ORS output record delimiter. The default value is line break \ n.

   RS input record delimiter. The default value is line break \ n.

   Cat test1.txt

   This is a test file.
   Welcome to Jacob's class.

   Cat test2.txt

   Hello the world.
   Wow, I'm overwhelmed.
   Ask for more.

   # Output the current line number of the current document

   Awk '{print FNR}' test1.txt test2.txt

   # Use the two documents as a whole input stream and enter the current row number through NR
   

   Awk '{print Nr}' test1.txt test2.txt

   # Output the current number of fields for each row

   Awk '{print NF}' test1.txt

   # Built-in variable FS field delimiter

   Awk 'in in {FS = "[:]"} {print $1} '/etc/passwd

   # Output field case delimiter
   

   Awk 'in in {OFS = "-"} {print $1, $2, $3} 'test1.txt

   Cat test.txt

   Name = lianjie
   Age = 26
   Tel = 18219995524
   
   Name = ccc
   Age = 20
   Tel = 13899246656
   
   Name = Alex
   Age = 25
   Tel = 19812345623

   Awk 'in in {FS = "\ n"; RS = ""} {print $1, $2, $3, $4} 'test.txt
   Name = lianjie age = 26 Tel = 18219995524
   Name = CCC age = 20 Tel = 13899246656
   Name = Alex age = 25 Tel = 19812345623

   Awk 'in in {FS = "\ n"; RS = ""} {print $1} 'test.txt
   

4. Expressions and operators

   Operator

   + Add

   -Subtraction

   * Multiplication
   

   /Division

   % Remainder

   ^ Power Operation

   ++ Auto-increment 1
   

   -- Auto-minus 1

   + = (X + = 9 is equivalent to X = x + 9)

   -= (X-= 9 is equivalent to X = X-9)

   * = (X * = 9 is equivalent to X = x * 9)
   

   /= (X/= 9 is equivalent to X = x/9)

   > Greater

   <Less

   > = Greater than or equal
   

   <= Less than or equal
   

   ! = Not equal

   ~ Match

   !~ Not worthy

   &

   | Or

   Echo 'test' | awk 'X = 2 {print x + 3 }'

   Echo 'test' | awk 'X = 2, y = 3 {print x * 3, y * 3 }'

   Awk '/^ $/{print x + = 1}' test.txt # Count all blank rows
   

   Awk '/^ $/{x + = 1} end {print x}' test.txt # print the total number of blank rows

   Awk-F: '$1 ~ /Root/{print $7} '/etc/passwd

   Awk-F: '$3> 500 {print $1}'/etc/passwd

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