6.24. Review
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| Unless otherwise noted, the examples in this section use the following datafile , repeated periodically for your convenience.
Example 6.161.% nawk '{if ( > 15 ){ print " has a high rating"}\ else print "---NOT A COMPETITOR---"}' datafile Joel---NOT A COMPETITOR--- Sharon has a high rating Chris has a high rating May---NOT A COMPETITOR--- Derek has a high rating Susan has a high rating TJ---NOT A COMPETITOR--- Val---NOT A COMPETITOR--- Sheri---NOT A COMPETITOR--- EXPLANATION The if statement is an action statement. If there is more than one statement following the expression, it must be enclosed in curly braces. (Curly braces are not required in this example, because there is only one statement following the expression.) The expression reads: if the eighth field is greater than 15 , print the third field and the string has a high rating ; else print the third field and “ “ “NOT A COMPETITOR “ “ “ . Example 6.162.% nawk '{i=1; while(i<=NF && NR < 2){print $i; i++}}' datafile northwest NW Joel Craig 3.0 .98 3 4 EXPLANATION The user -defined variable i is assigned 1. The while loop is entered and the expression tested . If the expression evaluates true, the print statement is executed; the value of the ith field is printed. The value of i is printed, next the value is incremented by 1, and the loop is reentered. The loop expression will become false when the value of i is greater than NF and the value of NR is 2 or more. The variable i will not be reinitialized until the next record is entered.
Example 6.163.% nawk '{ for( i=3 ; i <= NF && NR == 3 ; i++ ){ print $i }}' datafile Chris Foster 2.7 .8 2 18 EXPLANATION This is similar to the while loop in functionality. The initialization, test, and loop control statements are all in one expression. The value of i ( i = 3 ) is initialized once for the current record. The expression is then tested. If i is less than or equal to NF , and NR is equal to 3 , the print block is executed. After the value of the i th field is printed, control is returned to the loop expression. The value of i is incremented and the test is repeated. Example 6.164.(The Command Line) % cat nawk.sc4 # Awk script illustrating arrays BEGIN{OFS="\t"} { list[NR] = } # The array is called list. The index is # the number of the current record. The value of the # first field is assigned to the array element. END{ for( n = 1; n <= NR; n++){ print list[n]} # for loop is used to loop through the array. } (The Command Line) % nawk -f nawk.sc4 datafile northwest western southwest southern southeast eastern northeast north central EXPLANATION The array, list , uses NR as an index value. Each time a line of input is processed , the first field is assigned to the list array. In the END block, the for loop iterates through each element of the array. Example 6.165.(The Command Line) % cat nawk.sc5 # Awk script with special for loop /north/{name[count++]=} END{ print "The number living in a northern district: " count print "Their names are: " for ( i in name ) # Special nawk for loop is used to print name[i] # iterate through the array. } % nawk -f nawk.sc5 datafile The number living in a northern district: 3 Their names are: Joel TJ Val EXPLANATION Each time the regular expression north appears on the line, the name array is assigned the value of the third field. The index count is incremented each time a new record is processed, thus producing another element in the array. In the END block, the special- for loop is used to iterate through the array.
Example 6.166.(The Command Line) % cat nawk.sc6 # Awk and the special for loop {region[]++} # The index is the first field of each record END{for(item in region){ print region[item], item } } % nawk -f nawk.sc6 datafile 1 central 1 northwest 1 western 1 southeast 1 north 1 southern 1 northeast 1 southwest 1 eastern % nawk -f nawk.sc6 datafile3 4 Mary 2 Tom 1 Alax 1 Bob 1 Sean EXPLANATION The region array uses the first field as an index. The value stored is the number of times each region was found. The END block uses the awk special- for loop to iterate through the array called region . | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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EAN: 2147483647
Pages: 454