nix

• General Syntax of awk: awk -f {awk program file} filename

• The format of awk program looks like:

[pattern] {
Action 1
Action 2
..Action N
}

• Summery of common awk metacharacters:

• Built in awk variables

• Ex: create a plain file "inven" with the contents of last 4 lines.

$awk '{ print $1 $2 "--> Rs." $3 * $4 }' invent        /* $1, $2, $3, and $4 stand for field 1, 2, 3, 4 respectively in a record */

$vi prn_pen.awk
/Pen/ { print $3 }   ## /Pen/ is the searching pattern ##
$awk -f prn_pen.awk invent

$vi comp_inv.awk
$3>5 { print $0 }   ## $3>5, select the record that the value of column3 larger than 5, $0 stands for all fields in a record ##
$ awk -f comp_inv.awk invent          

$vi def_var.awk
{
         print "Printing Rec. #" NR "(" $0 "), and # of field for this record is " NF

}
$awk -f def_var.awk inven

• User defined variables and printf in awk
  Ex:
  $vi bill.awk
  BEGIN {                 ## BEGIN pattern, perform BEGIN actions before the first line (Record) has been read from database file ##
      printf "---------------------------\n"
      printf "Account\n"
      printf "---------------------------\n"
  }
  {
      total = $3 * $4  ## user defined variable ##
      recno = $1        ## user defined variable ##
      item = $2          ## user defined variable ##
      gtotal += total
      printf "%2d %-10s Rs.%7.2f\n", recno, item, total    ## Just like printf() in C lnaguage ##
  }
  END {                     /* END pattern, perform END actions after reading all lines (RECORD) from the database file */
      printf "---------------------------\n"
      printf "\tTotal Rs. %7.2f\n" ,gtotal
      printf "---------------------------\n"
  }
  $ awk -f bill.awk inven

• if condition in awk
  Syntax:
  if ( condition ){
      statement 1
      statement 2
      ...
      statement N
  }else{
      statement 1
      statement 2
      ...
      statement N
  }

• Ex:
  $vi math.awk
  BEGIN {
     myprompt = "(To Stop press CTRL+D) > "
     printf "Welcome to Addtion calculation awk program\n"
     printf "%s" ,myprompt
  }
  {
      no1 = $1
      op = $2
      no2 = $3
      ans = 0
      if ( op == "+" ){
          ans = $1 + $3
          printf "%d %c %d = %d\n" ,no1,op,no2,ans
          printf "%s" ,myprompt
      }else{
          printf "Opps!Error I only know how to add.\nSyntax: number1 + number2\n"
          printf "%s" ,myprompt
      }
  }
  END {
      printf "\nGoodbye %s\n" , ENVIRON["USER"]
  }
  $awk -f math.awk

• ENVIRON is the one of the predefined system variable that is array. ENVIRON can be used to access environment variables.

• loop in awk
  Syntax:
  for (expr1; condition; expr2){
             statement 1
             statement 2
             statement N
  }
  while (condition){
             statement1
             statement2
             statementN
  }

• Ex:
  $vi for.awk
  BEGIN{
             printf "Press ENTER to continue with for loop example\n"
  }
  {
             sum = 0
             i = 1
             for (i=1; i<=10; i++){
                       sum += i
             }
             printf "Sum for 1 to 10 numbers = %d \nGoodbye!\n", sum
             exit 1
  }
  $awk -f for.awk
  Ex:
  $vi while.awk
  {
             no = $1
             remn = 0
             while ( no > 1 ){
                       remn = no % 10
                       no /= 10
                       printf "%d" ,remn
             }
             printf "\nNext number please (CTRL+D to stop):"
  }
  #awk -f while.awk

• Ex: copy files
  $vi filelist.conf
  ~/1.txt /tmp
  ~/2.txt /tmp
  $vi cp.awk
  BEGIN{
  }
  {
             sfile = $1
             dfile = $2
             cpcmd = "cp " $1 " " $2
             printf "Copying %s to %s\n",sfile,dfile
             system(cpcmd)    ## system() function execute given system command ##
  }
  END{
  }
  $awk -f cp.awk filelist.conf

• Ex: remove files
  $vi rm.awk
  {
             dcmd = "rm " $1
             if( system(dcmd) != 0 )
                       printf "rm command not successful\n"
             else
                       printf "rm command is successful and %s file is removed \n", $1
  }
  $awk -f rm.awk

• getline
  Syntax:
  getline < "file-name"                 /* read input from file */
  "command" | getline                 /* read input from pipe */

• Ex:
  $vi getline.awk
  BEGIN{
             printf "Your name please:"
             getline na < "-"
             printf "%s your age please:",na
             getline age < "-"
             age++
             printf "Hello %s, next year you will be %d\n", na, age
  }
  $awk -f getline.awk
  $vi date.awk
  BEGIN{
             "date" | getline
             print $0
             "date" | getline today
             print $today
  }
  $awk -f date.awk