AWK - Unix

What is AWK ?

Scans a set of input lines, searching for lines that match any set of patterns and take a specified action for each pattern on each line that matches the pattern

 Usage

awk ‘pattern-action statements’ optional list of input files

e.g. awk ‘{print $1, $2}’ file1 file2

OR

awk -f programfile optional list of input files

where programfile is the file where the pattern-action statements are stored

 Fields

Record is the sequence of characters separated by a newline character

Fields in a record are separated by sequence of blanks or tabs

$0 refers to the entire record

$1 refers to the first field

$2 refers to the second field

Printing

{ print }

prints all the records

{print $1 $3}

prints the first and third fields of each of the input line

BuiltIn Variables

ARGC  number of command line arguments

ARGV  array of command line arguments

FILENAME  name of current input file

FNR  record number in current file

NR   number of current record

NF  number of fields in the record

OFS  Output field separator

ORS  Output record separator

 Examples
Print last field of each input line

{ print $NF }

Print total number of input lines

END {print NR}

Print input lines with more than 4 fields

NF > 4

Print the total no of lines that match string “abc”

/abc/  {nlines++} END {print nlines}

cos(x)

log(x)

exp(x)

rand(x)

sin(x)

sqrt(x)

srand(x)

BuiltIn String Functions

index(s,t)  returns position of t in s

length(s)  returns length of s

split(s,a)  splits into array a on FS

sub(s,r)  substitutes s for first r

substr(s,p)  returns suffix of string starting at position p

Control Flow Statements

if (expression) stat1 else stat2

while (expression) stat

for (expr1;expr2;expr3) stat

do stat while (expr)

break

continue

next

exit(expr)

return(expr)

Example scenarios