6.12. Review

The examples in this section use the following sample database, called datafile, repeated periodically for your convenience.

% cat datafile
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

6.12.1 Equality Testing

Example 6.62.


% awk '$7 == 5' datafile

western                WE      Sharon Kelly          5.3   .97   5     23

eastern                EA      Susan Beal            4.4   .84   5     20

north                  NO      Val Shultz            4.5   .89   5      9

central                CT      Sheri Watson          5.7   .94   5     13

EXPLANATION

If the seventh field ($7) is equal to the number 5, the record is printed.

Example 6.63.


% awk '$2 == "CT"{print $1, $2}' datafile

central               CT

EXPLANATION

If the second field is equal to the string CT, fields one and two ($1, $2) are printed. Strings must be quoted.

Example 6.64.


% awk '$7 != 5' datafile

northwest             NW    Joel Craig       3.0    .98   3     4

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

northeast             NE    TJ Nichols       5.1    .94   3    13

EXPLANATION

If the seventh field ($7) is not equal to the number 5, the record is printed.

6.12.2 Relational Operators

Example 6.65.


% awk '$7 < 5 {print $4, $7}' datafile

Craig 3

Foster 2

Chin 4

Johnson 4

Nichols 3

EXPLANATION

If the seventh field ($7) is less than 5, fields 4 and 7 are printed.

Example 6.66.


% awk '$6 > .9 {print $1, $6}' datafile

northwest .98

western .97

southern .95

northeast .94

central .94

EXPLANATION

If the sixth field ($6) is greater than .9, fields 1 and 6 are printed.

Example 6.67.


% awk '$8 <= 17 { print $8}' datafile

4

15

17

13

9

13

EXPLANATION

If the eighth field ($8) is less than or equal to 17, it is printed.

Example 6.68.


% awk '$8 >= 17 {print $8}' datafile

23

18

17

20

EXPLANATION

If the eighth field ($8) is greater than or equal to 17, the eighth field is printed.

6.12.3 Logical Operators (`&&`, `||`)

Example 6.69.


% awk '$8 > 10 && $8 < 17' datafile

southern              SO        May Chin               5.1    .95    4    15

northeast             NE        TJ Nichols             5.1    .94    3    13

central               CT        Sheri Watson           5.7    .94    5    13

EXPLANATION

If the eighth field ($8) is greater than 10 AND less than 17, the record is printed. The record will be printed only if both expressions are true.

Example 6.70.


% awk '$2 == "NW" || $1 ~ /south/{print $1, $2}' datafile

northwest NW

southwest SW

southern SO

southeast SE

EXPLANATION

If the second field ($2) is equal to the string NW OR the first field ($1) contains the pattern south, the first and second fields ($1, $2) are printed. The record will be printed if only one of the expressions is true.

6.12.4 Logical NOT Operator (`!`)

Example 6.71.


% awk '!($8 == 13){print $8}' datafile

4

23

18

15

17

20

9

EXPLANATION

If the eighth field ($8) is equal to 13, the ! (NOT operator) NOTs the expression and prints the eighth field ($8). The ! is a unary negation operator.

6.12.5 Arithmetic Operators

Example 6.72.


% awk '/southern/{print $5 + 10}' datafile

15.1

EXPLANATION

If the record contains the regular expression southern, 10 is added to the value of the fifth field ($5) and printed. Note that the number prints in floating point.

Example 6.73.


% awk '/southern/{print $8 + 10}' datafile

25

EXPLANATION

If the record contains the regular expression southern, 10 is added to the value of the eighth field ($8) and printed. Note that the number prints in decimal.

Example 6.74.


% awk '/southern/{print $5 + 10.56}' datafile

15.66

EXPLANATION

If the record contains the regular expression southern, 10.56 is added to the value of the fifth field ($5) and printed.

Example 6.75.


% awk '/southern/{print $8 - 10}' datafile

5

EXPLANATION

If the record contains the regular expression southern, 10 is subtracted from the value of the eighth field ($8) and printed.

Example 6.76.


% awk '/southern/{print $8 / 2}' datafile

7.5

EXPLANATION

If the record contains the regular expression southern, the value of the eighth field ($8) is divided by 2 and printed.

Example 6.77.


% awk '/northeast/{print $8 / 3}' datafile

4.33333

EXPLANATION

If the record contains the regular expression northeast, the value of the eighth field ($8) is divided by 3 and printed. The precision is five places to the right of the decimal point.

Example 6.78.


% awk '/southern/{print $8 * 2}' datafile

30

EXPLANATION

If the record contains the regular expression southern, the eighth field ($8) is multiplied by 2 and printed.

Example 6.79.


% awk '/northeast/ {print $8 % 3}' datafile

1

EXPLANATION

If the record contains the regular expression northeast, the eighth field ($8) is divided by 3 and the remainder (modulus) is printed.

Example 6.80.


% awk '$3 ~ /^Susan/\

{print "Percentage: "$6 + .2 " Volume: " $8}' datafile

Percentage: 1.04 Volume: 20

EXPLANATION

If the third field ($3) begins with the regular expression Susan, the print function prints the result of the calculations and the strings in double quotes.

6.12.6 Range Operator

Example 6.81.


% awk '/^western/,/^eastern/' datafile

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

EXPLANATION

All records within the range beginning with the regular expression western are printed until a record beginning with the expression eastern is found. Records will start being printed again if the pattern western is found and will continue to print until eastern or the end of the file is reached.

6.12.7 Conditional Operator

Example 6.82.


% awk '{print ($7 > 4 ? "high "$7 : "low "$7)}' datafile

low 3

high 5

low 2

low 4

low 4

high 5

low 3

high 5

high 5

EXPLANATION

If the seventh field ($7) is greater than 4, the print function gets the value of the expression after the question mark (the string high and the seventh field); else the print function gets the value of the expression after the colon (the string low and the value of the seventh field).

6.12.8 Assignment Operators

Example 6.83.


% awk '$3 == "Chris"{ $3 = "Christian"; print}' datafile

southwest SW Christian Foster 2.7 .8 2 18

EXPLANATION

If the third field ($3) is equal to the string Chris, the action is to assign Christian to the third field ($3) and print the record. The double equal tests its operands for equality, whereas the single equal is used for assignment.

Example 6.84.


% awk '/Derek/{$8 += 12; print $8}' datafile

29

EXPLANATION

If the regular expression Derek is found, 12 is added and assigned to (+=), the eighth field ($8), and that value is printed. Another way to write this is $8 = $8 + 12.

Example 6.85.


% awk '{$7 %= 3; print $7}' datafile

0

2

2

1

1

2

0

2

2

EXPLANATION

For each record, the seventh field ($7) is divided by 3, and the remainder of that division (modulus) is assigned to the seventh field and printed.

< Day Day Up >

6.12. Review

6.12.1 Equality Testing

Example 6.62.

Example 6.63.

Example 6.64.

6.12.2 Relational Operators

Example 6.65.

Example 6.66.

Example 6.67.

Example 6.68.

6.12.3 Logical Operators (&&, ||)

Example 6.69.

Example 6.70.

6.12.4 Logical NOT Operator (!)

Example 6.71.

6.12.5 Arithmetic Operators

Example 6.72.

Example 6.73.

Example 6.74.

Example 6.75.

Example 6.76.

Example 6.77.

Example 6.78.

Example 6.79.

Example 6.80.

6.12.6 Range Operator

Example 6.81.

6.12.7 Conditional Operator

Example 6.82.

6.12.8 Assignment Operators

Example 6.83.

Example 6.84.

Example 6.85.

6.12.3 Logical Operators (`&&`, `||`)

6.12.4 Logical NOT Operator (`!`)