awk

Question 1

awk definition

Answer 1

pattern matching, record manipulation, programming.

awk processes files where the content is regarded as a set of records containing a consistent set of fields (like a table).

Question 2

awk syntax

Answer 2

awk options ‘selection_criteria {action}’ file(s)

ex.

awk /Dairy/ {print $1,$3} gdbase

command Options SelectionCriteria Action Filename(s)

Question 3

“For each matching ___, perform the given ___.”

Answer 3

Line
Action

Question 4

If no action is specified, the default action is ___. In this case awk acts like ___.

Answer 4

Print
grep

Question 5

The action print without field specifiers (such as $1 and $3) outputs

Answer 5

each line matched

Question 6

If no selection criteria are specified, all lines are selected for processing. In this case awk acts like?

Answer 6

cat

Question 7

awk’s key distinction is that specific pieces of a record (or line) can be ___ & ___ ?

Answer 7

selected and processed.

grep just selects the line, and does no processing.

Question 8

awk is only possible if the input is organized in

Answer 8

some regular manner

Question 9

awk ‘/Fish/ {print $1}’ gdbase

Answer 9

awk ‘/Fish/ {print $1}’ gdbase

• This prints the first field of lines that contain the string “Fish”.
• $ is the field operator – it indicates the field of the record to consider. For example, $1 is
  interpreted as the value of the record’s first field.

Note: $0 is a convenience variable that represents the entire line.

Question 10

awk ‘/Fish/ {print $1, $3, $2}’ gdbase

Answer 10

awk ‘/Fish/ {print $1, $3, $2}’ gdbase

• Prints fields 1, 3, 2 for each record, with a space between each. The comma indicates that a space will separate the fields.
• Note: awk views a string as a variable unless it is inside double quotes or inside the slashes / /.
• Strings inside / / are regular expression strings for pattern matching.
• For example, numbers are regarded as a string in this context:
  awk ‘{print 1234 $1} gdb

Question 11

Selecting Lines by Field Value

awk ‘$5 == ”y” {print $1, $3, $2}’ gdbase

Answer 11

Selecting Lines by Field Value
awk ‘$5 == ”y” {print $1, $3, $2}’ gdbase

• Lines where field 5 contains only the character y, are selected for processing.
• Processing here is print field 1 followed by field 3 then field 2

Question 12

Use Other Relational Operators for Selecting Lines by Field Value
awk ‘$5 == ”y” && $3<4.00 {print $1, $3, $2}’ gdbase

Answer 12

Use Other Relational Operators for Selecting Lines by Field Value
awk ‘$5 == ”y” && $3<4.00 {print $1, $3, $2}’ gdbase

• Use && as logical AND and || as logical OR.
• Enclose expressions in brackets () to group them like in Java.
• The NOT operator is !

Question 13

You can use these operators between target strings:

awk ‘/Dairy/||/Meat/ && $3<4.00 {print $1, $3, $2}’ gdbase

Answer 13

You can use these operators between target strings:
awk ‘/Dairy/||/Meat/ && $3<4.00 {print $1, $3, $2}’ gdbase

• This will print fields 1, 3 and 2 for lines that contain “Dairy” or lines that contain “Meat” where the 3rd field is less than 4.00.

Question 14

accumulator variable

Answer 14

printing sum

Question 15

Can Search a Field for a Target

awk ‘$3~/.89$/’ gdbase

Answer 15

Can Search a Field for a Target
awk ‘$3~/.89$/’ gdbase

• Use the ~ operator to search the 3rd field for the string .89 at the end of the field, and select those records for processing.

Question 16

Defined variables
 NF =>
 NR =>
 FS =>
 OFS =>
 ORS =>

Answer 16

 NF => number of fields in a record
 NR => number of records (lines) in the file
 FS => Field Separator
 OFS => Output Field Separator
 ORS => Output Record Separator

Question 17

NF (Defined variables)

Answer 17

number of fields in a record

Question 18

NR

Answer 18

NR => number of records (lines) in the file