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6.16. ReviewThe examples in this section, unless noted otherwise, use the following datafile, repeated periodically for your convenience.
6.16.1 Increment and Decrement OperatorsExample 6.105.% nawk '/^north/{count += 1; print count}' datafile 1 2 3 EXPLANATION If the record begins with the regular expression north, a user-defined variable, count, is created; count is incremented by 1 and its value is printed. Example 6.106.% nawk '/^north/{count++; print count}' datafile 1 2 3 EXPLANATION The auto-increment operator increments the user-defined variable count by 1. The value of count is printed. Example 6.107.% nawk '{x = $7--; print "x = "x ", $7 = "$7}' datafile x = 3, $7 = 2 x = 5, $7 = 4 x = 2, $7 = 1 x = 4, $7 = 3 x = 4, $7 = 3 x = 5, $7 = 4 x = 3, $7 = 2 x = 5, $7 = 4 x = 5, $7 = 4 EXPLANATION After the value of the seventh field ($7) is assigned to the user-defined variable x, the auto-decrement operator decrements the seventh field by 1. The value of x and the seventh field are printed. 6.16.2 Built-In VariablesExample 6.108.% nawk '/^north/{print "The record number is " NR}' datafile The record number is 1 The record number is 7 The record number is 8 EXPLANATION If the record begins with the regular expression north, the string The record number is and the value of NR (record number) are printed. Example 6.109.% nawk '{print NR, $0}' datafile 1 northwest NW Joel Craig 3.0 .98 3 4 2 western WE Sharon Kelly 5.3 .97 5 23 3 southwest SW Chris Foster 2.7 .8 2 18 4 southern SO May Chin 5.1 .95 4 15 5 southeast SE Derek Johnson 4.0 .7 4 17 6 eastern EA Susan Beal 4.4 .84 5 20 7 northeast NE TJ Nichols 5.1 .94 3 13 8 north NO Val Shultz 4.5 .89 5 9 9 central CT Sheri Watson 5.7 .94 5 13 EXPLANATION The value of NR, the number of the current record, and the value of $0, the entire record, are printed.
Example 6.110.% nawk 'NR==2,NR==5{print NR, $0}' datafile 2 western WE Sharon Kelly 5.3 .97 5 23 3 southwest SW Chris Foster 2.7 .8 2 18 4 southern SO May Chin 5.1 .95 4 15 5 southeast SE Derek Johnson 4.0 .7 4 17 EXPLANATION If the value of NR is in the range between 2 and 5 (record numbers 25), the number of the record (NR) and the record ($0) are printed. Example 6.111.% nawk '/^north/{print NR, $1, $2, $NF, RS}' datafile 1 northwest NW 4 7 northeast NE 13 8 north NO 9 EXPLANATION If the record begins with the regular expression north, the number of the record (NR), followed by the first field, the second field, the value of the last field (NF preceded by a dollar sign), and the value of RS (a newline) are printed. Because the print function generates a newline by default, RS will generate another newline, resulting in double spacing between records. Use the following datafile2 for Examples 6.112 and 6.113.
Example 6.112.% nawk -F: 'NR == 5{print NF}' datafile2 7 EXPLANATION The field separator is set to a colon at the command line with the F option. If the number of the record (NR) is 5, the number of fields (NF) is printed. Example 6.113.% nawk 'BEGIN{OFMT="%.2f";print 1.2456789,12E-2}' datafile2 1.25 0.12 EXPLANATION OFMT, the output format variable for the print function, is set so that floating-point numbers will be printed with a decimal-point precision of two digits. The numbers 1.23456789 and 12E2 are printed in the new format.
Example 6.114.% nawk '{$9 = $6 * $7; print $9}' datafile 2.94 4.85 1.6 3.8 2.8 4.2 2.82 4.45 4.7 EXPLANATION The result of multiplying the sixth field ($6) and the seventh field ($7) is stored in a new field, $9, and printed. There were eight fields; now there are nine. Example 6.115.% nawk '{$10 = 100; print NF, $9, $0}' datafile 10 northwest NW Joel Craig 3.0 .98 3 4 100 10 western WE Sharon Kelly 5.3 .97 5 23 100 10 southwest SW Chris Foster 2.7 .8 2 18 100 10 southern SO May Chin 5.1 .95 4 15 100 10 southeast SE Derek Johnson 4.0 .7 4 17 100 10 eastern EA Susan Beal 4.4 .84 5 20 100 10 northeast NE TJ Nichols 5.1 .94 3 13 100 10 north NO Val Shultz 4.5 .89 5 9 100 10 central CT Sheri Watson 5.7 .94 5 13 100 EXPLANATION A tenth field ($10) is assigned 100 for each record. This is a new field. The ninth field ($9) does not exist, so it will be considered a null field. The number of fields is printed (NF), followed by the value of $9, the null field, and the entire record ($0). The value of the tenth field is 100. 6.16.3 BEGIN PatternsExample 6.116.% nawk 'BEGIN{print "---------EMPLOYEES---------"}' ---------EMPLOYEES--------- EXPLANATION The BEGIN pattern is followed by an action block. The action is to print out the string EMPLOYEES before opening the input file. Note that an input file has not been provided and awk does not complain because any action preceded by BEGIN occurs first, even before awk looks for an input file. Example 6.117.% nawk 'BEGIN{print "\t\t---------EMPLOYEES-------\n"}\ {print $0}' datafile ---------EMPLOYEES------- northwest NW Joel Craig 3.0 .98 3 4 western WE Sharon Kelly 5.3 .97 5 23 southwest SW Chris Foster 2.7 .8 2 18 southern SO May Chin 5.1 .95 4 15 southeast SE Derek Johnson 4.0 .7 4 17 eastern EA Susan Beal 4.4 .84 5 20 northeast NE TJ Nichols 5.1 .94 3 13 north NO Val Shultz 4.5 .89 5 9 central CT Sheri Watson 5.7 .94 5 13 EXPLANATION The BEGIN action block is executed first. The title EMPLOYEES is printed. The second action block prints each record in the input file. When breaking lines, the backslash is used to suppress the carriage return. Lines can be broken at a semicolon or a curly brace. The following datafile2 is used for Example 6.118.
Example 6.118.% nawk 'BEGIN{ FS=":";OFS="\t"};/^Sharon/{print $1, $2, $8 }' datafile2 Sharon Kelly western 28 EXPLANATION The BEGIN action block is used to initialize variables. The FS variable (field separator) is assigned a colon. The OFS variable (output field separator) is assigned a tab (\t). After processing the BEGIN action block, awk opens datafile2 and starts reading input from the file. If a record begins with the regular expression Sharon, the first, second, and eighth fields ($1, $2, $8) are printed. Each field in the output is separated by a tab. 6.16.4 END PatternsThe following datafile is used for Examples 6.119 and 6.120.
Example 6.119.% nawk 'END{print "The total number of records is " NR}' datafile The total number of records is 9 EXPLANATION After awk has finished processing the input file, the statements in the END block are executed. The string The total number of records is is printed, followed by the value of NR, the number of the last record. Example 6.120.% nawk '/^north/{count++}END{print count}' datafile 3 EXPLANATION If the record begins with the regular expression north, the user-defined variable count is incremented by one. When awk has finished processing the input file, the value stored in the variable count is printed. 6.16.5 awk Script with BEGIN and ENDThe following datafile2 is used for Example 6.121.
Example 6.121.
# Second awk script-- awk.sc2
1 BEGIN{ FS=":"
print " NAME\t\tDISTRICT\tQUANTITY"
print "___________________________________________\n"
}
2 {print $1"\t " $3"\t\t" $7}
{total+=$7}
/north/{count++}
3 END{
print "---------------------------------------------"
print "The total quantity is " total
print "The number of northern salespersons is " count "."
}
(The Output)
4 % nawk -f awk.sc2 datafile2
NAME DISTRICT QUANTITY
___________________________________________
Joel Craig NW 4
Sharon Kelly WE 23
Chris Foster SW 18
May Chin SO 15
Derek Johnson SE 17
Susan Beal EA 20
TJ Nichols NE 13
Val Shultz NO 9
Sheri Watson CT 13
---------------------------------------------
The total quantity is 132
The number of northern salespersons is 3.
EXPLANATION
The remaining examples in this section use the following datafile, repeated periodically for your convenience.
6.16.6 The printf FunctionExample 6.122.% nawk '{printf "$%6.2f\n",$6 * 100}' datafile $ 98.00 $ 97.00 $ 80.00 $ 95.00 $ 70.00 $ 84.00 $ 94.00 $ 89.00 $ 94.00 EXPLANATION The printf function formats a floating-point number to be right-justified (the default) with a total of 6 digits, one for the decimal point, and two for the decimal numbers to the right of the period. The number will be rounded up and printed. Example 6.123.% nawk '{printf "|%-15s|\n",$4}' datafile |Craig| |Kelly | |Foster | |Chin | |Johnson| |Beal | |Nichols| |Shultz| |Watson| EXPLANATION A left-justified, 15-space string is printed. The fourth field ($4) is printed enclosed in vertical bars to illustrate the spacing. 6.16.7 Redirection and PipesExample 6.124.% nawk '/north/{print $1, $3, $4 > "districts"}' datafile % cat districts northwest Joel Craig northeast TJ Nichols north Val Shultz EXPLANATION If the record contains the regular expression north, the first, third, and fourth fields ($1, $3, $4) are printed to an output file called districts. Once the file is opened, it remains open until closed or the program terminates. The filename "districts" must be enclosed in double quotes. Example 6.125.% nawk '/south/{print $1, $2, $3 >> "districts"}' datafile % cat districts southwest SW Chris southern SO May southeast SE Derek EXPLANATION If the record contains the pattern south, the first, second, and third fields ($1, $2, $3) are appended to the output file districts.
6.16.8 Opening and Closing a PipeExample 6.126.# awk script using pipes -- awk.sc3 1 BEGIN{ 2 printf " %-22s%s\n", "NAME", "DISTRICT" print "--------------------------------------" 3 } 4 /west/{count++} 5 {printf "%s %s\t\t%-15s\n", $3, $4, $1| "sort +1" } 6 END{ 7 close "sort +1" printf "The number of sales persons in the western " printf "region is " count "." } (The Output) % nawk -f awk.sc3 datafile 1 NAME DISTRICT 2 -------------------------------------------------- 3 Susan Beal eastern May Chin southern Joel Craig northwest Chris Foster southwest Derek Johnson southeast Sharon Kelly western TJ Nichols northeast Val Shultz north Sheri Watson central The number of sales persons in the western region is 3. EXPLANATION
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