Expressions

• Constants
  • String constant : "Asia", "hello, world", ""
  • Numeric constant : 1127, 0.707E-1, 1e6 (¸ðµç ¼ö´Â floating point ÇüÅ·ΠÀúÀå)

• Variables
  • User-defined : functionµµ, built-in variableµµ, field variableµµ ¾Æ´Ñ °æ¿ì
  • Built-In Variables: FNR, NF, NR...
  • Field Variables: $1, $2, ..., $NF, $0

  ¿¹Á¦:
        BEGIN                 { FS = OFS = "\t" }
          $4 == "North America"    { $4 = "NA"}
         $4 == "South America"    { $4 = "SA" }
                       { print }
   

• Arithmetic Operators : +, -, *, /, % and ^

• Comparison Operators : <, <=, ++, !=, >=, >, , !~\

  ¿¹Á¦:
                $4 ~ /Asia/
   

• Logical Operators : &&(AND), || (OR), !(NOT)

• Conditional Expressions : ? :

• Assignment Operators: var = expr

  ¿¹Á¦:
           $4 == "Asia"    { pop = pop + $3, n = n + 1 }
       END        { print "Total population of the", n, 
                                "Asian countries is", pop, "million." }
   

• Increment and Decrement Operators : ++, --

• Built-in Arithmetic Functions : µµÇ¥

  ¿¹Á¦:
        randint = int (n * rand()) + 1
   

• String Operators : concatenation

  ¿¹Á¦:
        { print NR ":" $0}
   

• Strings as Regular Expressions

  ¿¹Á¦:
    BEGIN {
    sign = "[+-]?"
    decimal = "[0-9]+[.]?[0-9]*"
    fraction = "[.][0-9]+"
    exponent = "([eE]" sign "[0-9]+)?"
    number = "^" sign "(" decimal "|" fraction ")" exponent "&"
           }
         $0 ~ number
   

  ¿¹Á¦:
           $0 ~ /(\+|-)[0-9]+/
           $0 ~ "(\\ +|-)[0-9]+"
   

• Built-In String Functions

  ¿¹Á¦:
        index("banana", "an") 
          returns 2
           Ex 9)
               { $1 = substr($1, 1, 3); print $0 }
   

• Number or String ? : Automatically converted

  ¿¹Á¦:
    making string : number ""
         Ex 10) 
           $1 "" == $2   
       making number : string + 0
         Ex 11)
           $1 + 0 == $2 + 0