The AWK Language

1. 제14강 : The AWK Language The AWK Language

2. While reading each line from file Pattern matching, Action File sample Koh 4.00 0 Lee 3.75 0 Park 4.00 10 Kim 5.00 20 Song 5.50 22 Han 4.25 18 pattern action • awk ‘$3>0 {print $1, $2, $3}’ sample awk program • Example • awk ‘$3==0 {print $1}’ sample • awk ‘$3>0 {print $1, $2*$3}’ sample • 3) awk ‘{print $1}’ sample : action with no pattern Output 2 Park 40 Kim 100 Song … Han … Output 1 Koh Lee

3. Structure of an awk program: Syntax awk ‘program’ input_files awk –f program_file input_files pattern {action} pattern {action} … • Simple output • {print} entire line • {print $0} entire line • {print NF $1} NF : built-in var • {print $1, $NF} print 1st & last field • {print NR $0} line_# & line • {print “total pay for”, $1, “is”, $2*$3} Variables ? See next slide …

4. Variables User-defined : 0 or null init Built-in Fields : $0 $1 $2 … Printf format conversion % c : ASCII char % d : decimal number % o : unsigned octal % f, % e, % s, …. Example {printf(“pay for % s is w% .2f \n”, $1, $2*$3)} Built-in vars ARGC : # of command line args ARGV : array of command line args FILENAME : name of input file FNR : record # in current file FS : field separator NF : # of fields in current rec NR: # of recs read so far OFMT : output format for numbers OFS : output field separator RS : input rec separator File sample Koh 4.00 0 Lee 3.75 0 Park 4.00 10 Kim 5.00 20 Song 5.50 22 Han 4.25 18 output Pay for Han is w76.50

5. File sample Koh 4.00 0 Lee 3.75 0 Park 4.00 10 Kim 5.00 20 Song 5.50 22 Han 4.25 18 • Selection • By computation • awk ‘$2*$3>50 {printf(“$%.2f for %s\n”, $2*$3, $1)}’ sample • By text content • awk ‘$1==“Susie” {print …}’ sample • combinations (&& || !) • awk ‘$2 >= 4 || $3 >= 30 {printf …}’ sample Output $100.00 for Kim $121.00 for Song $76.50 for Han

6. File sample Koh 4.00 0 Lee 3.75 0 Park 4.00 10 Kim 5.00 20 Song 5.50 22 Han • Pattern BEGIN & END • BEGIN { statements } • Becomes TRUE once before any input has been read • END { statements } • Becomes TRUE once after all input has been read • example try sf11 BEGIN {print “Header line here”} $3>15 {emp=emp+1} END {print emp, “men worked more than 15 hours”} emp : user- defined var initialized value zero user var can hold strings as well as numbers $2>maxrate {maxrate=$2, maxemp=$1} END {print “max. rate:”, maxrate, “for”, maxemp}

7. names var = Koh Lee Park Kim separated by blanks {names=names $1 ““} END {print names} {print $1, length($1)} • String concatenation • Built-in string functions • match(s, r) : the leftmost longest substr in s that is matched by the regular expr r • split(s, a, fs) : splits the str s into the array a according to the separator fs and returns # of elements • sub(r, s, t) : find leftmost longest substr • gsub(r, s, t) : global substitution

8. string examples • $4 ~/Asia/ {Action} • 4th field contains Asia • $0 !~/Asia/ {Action} • line doesn’t contain Asia • $2 !~/^[0-9]+$/ {Action} • 2nd field not a string of digits

9. Built-in arithmetic functions • atan2(y, x) : arctangent of y/x • cos(x) : cosine of x • exp(x) : ex • int(x) : integer part of x • log(x) : natural logarithm of x • rand() : random number • sin(x) : sine of x • sqrt(x) : square root of x • srand(x) : x is new seed for rand()

10. Control statements • if (expr) statement • if (expr) statementelsestatement • while (expr) statement • for (expr;expr;expr) statement • dostatementwhile (expr) • break • continue • Arrays { line[NR] = $0 } END { i=NR While (i>0) {…} }

11. Range patterns • pattern1, pattern2 { Action } • A range pattern matches each input line • from a line matched by pattern1 • to the next line matched by pattern2 • Example: Removing unwanted part #ifdef intel  pattern1 intel dependent code “remove” #elseif  pattern2 non-intel code #endif

12. Awk is • a UNIX command • Interpreter • Given a file, • Read line by line • Pattern match & take action • Text processing tool • More powerful than grep, sed, … • Filter • Given a text file • Read each line • Transforms them • Output lines