Linux/83.Displaying_Records_With_AWK.md at main · Akshayredekar07/Linux

Using NR Variable in awk with Relational Operators

NR (Number of Record) can be used with all relational operators to filter records in a file. Below are some examples:

Examples

Skip the First Two Records:
```
awk 'NR>2 {print $0}' FS="," emp.csv
```
Print the First Field of Records After the First Two:
```
awk 'NR>2 {print $1}' FS="," emp.csv
```
Display Only the 2nd and 4th Records:
```
awk 'NR==2 || NR==4 {print $0}' FS="," emp.csv
```
Output: Displays the full content of the 2nd and 4th records.
Display the First Field of the 2nd and 4th Records:
```
awk 'NR==2 || NR==4 {print $1}' FS="," emp.csv
```
Output: Displays only the first field of the 2nd and 4th records.

Display the 3rd and 4th Records:

awk 'NR>2 && NR<5 {print $0}' FS="," emp.csv

Display Records from the 2nd to the 4th:

awk 'NR>1 && NR<5 {print $0}' FS="," emp.csv

Display Records Between the 2nd and 4th (Inclusive):
```
awk 'NR==2, NR==4 {print $0}' FS="," emp.csv
```
Output: Displays records from the 2nd to the 4th.

Explanation of $0, $1, $2, ... in awk

In awk, each line of a file is treated as a record, and fields within a record are separated by the Field Separator (FS, default is whitespace).

$0: Refers to the entire record (the full line).
$1: Refers to the first field.
$2, $3, and so on refer to the respective fields.

Example Data (File: emp.csv)

100,Durga,1000,Mumbai
200,Bunny,2000,Hyderabad
300,Chinny,3000,Hyderabad
400,Vinny,4000,Chennai
500,Pinny,5000,Mumbai

Using awk with Examples

Print the Entire Line ($0):

awk '{print $0}' FS="," emp.csv

Output:

100,Durga,1000,Mumbai
200,Bunny,2000,Hyderabad
300,Chinny,3000,Hyderabad
400,Vinny,4000,Chennai
500,Pinny,5000,Mumbai

Print the First Field ($1):

awk '{print $1}' FS="," emp.csv

Output:

Print the Second Field ($2):

awk '{print $2}' FS="," emp.csv

Output:

Durga
Bunny
Chinny
Vinny
Pinny

Print the Third Field ($3):

awk '{print $3}' FS="," emp.csv

Output:

Print the Fourth Field ($4):

awk '{print $4}' FS="," emp.csv

Output:

Mumbai
Hyderabad
Hyderabad
Chennai
Mumbai

Advanced Examples

Print Specific Fields ($1 and $2):

awk '{print $1, $2}' FS="," emp.csv

Output:

100 Durga
200 Bunny
300 Chinny
400 Vinny
500 Pinny

Print Fields in a Custom Format:

awk '{print "ID:", $1, "Name:", $2, "Salary:", $3, "City:", $4}' FS="," emp.csv

Output:

ID: 100 Name: Durga Salary: 1000 City: Mumbai
ID: 200 Name: Bunny Salary: 2000 City: Hyderabad
ID: 300 Name: Chinny Salary: 3000 City: Hyderabad
ID: 400 Name: Vinny Salary: 4000 City: Chennai
ID: 500 Name: Pinny Salary: 5000 City: Mumbai

Print Only the Last Field ($NF):

awk '{print $NF}' FS="," emp.csv

Output:

Mumbai
Hyderabad
Hyderabad
Chennai
Mumbai

Print All Fields Except the Last ($(NF-1)):

awk '{for (i=1; i<NF; i++) printf $i ","; print ""}' FS="," emp.csv

Output:

100,Durga,1000,
200,Bunny,2000,
300,Chinny,3000,
400,Vinny,4000,
500,Pinny,5000,

Key Points

$0: Entire record (full line).
$1: First field.
$NF: Last field.
NF: Total number of fields in the current record.

Q) Consider the File: xy.txt

1.abc
2.def
3.ghi
4.jkl5.mno

What is the output of the following commands?

Command:
```
awk '{print $0;}' xy.txt
```
Explanation: It will print the entire file as it is.
Output:
```
1.abc
2.def
3.ghi
4.jkl5.mno
```
Command:
```
awk '{print $1;}' xy.txt
```
Explanation: It will print the entire file because the file contains only one column.
Output:
```
1.abc
2.def
3.ghi
4.jkl5.mno
```
Command:
```
awk '{print $2;}' xy.txt
```
Explanation: Nothing will be printed because there is no second column in the file.
Output: (No Output)

AWK Code into a Separate File

We can separate AWK code into a file and use the -f option to execute it.

Example

AWK Code File (x.txt):

BEGIN {print "BEGIN"}
{print $0}
END {print "END"}

Command:

awk -f x.txt FS="," emp.csv

Output:

BEGIN
eno,ename,esal,eaddr
100,Sunny,1000,Mumbai
200,Bunny,2000,Hyderabad
300,Chinny,3000,Hyderabad
400,Vinny,4000,Chennai
500,Pinny,5000,Mumbai
END

Filter Data Based on Conditions

List all employees where eaddr is Hyderabad:

awk '$4=="Hyderabad"{print $0}' FS="," emp.csv

Output:

200,Bunny,2000,Hyderabad
300,Chinny,3000,Hyderabad

List all employees where esal is greater than 2500:

awk '$3>2500{print $0}' FS="," emp.csv

Output:

eno,ename,esal,eaddr
300,Chinny,3000,Hyderabad
400,Vinny,4000,Chennai
500,Pinny,5000,Mumbai

Skip the header and filter records where esal is greater than 2500:

awk 'NR!=1 && $3>2500{print $0}' FS="," emp.csv

Output:

300,Chinny,3000,Hyderabad
400,Vinny,4000,Chennai
500,Pinny,5000,Mumbai

Search Records Using a String

Filter all records containing 20 in any field:

awk '/20/{print $0}' FS="," emp.csv

Output:

200,Bunny,2000,Hyderabad
20,Durga,5000,Hyderabad
50,Shiva,2020,Hyderabad

Filter records where the 3rd field contains 20:

awk '$3~/20/{print $0}' FS="," emp.csv

Output:

200,Bunny,2000,Hyderabad
50,Shiva,2020,Hyderabad

Exclude records where the 3rd field contains 20:

awk '$3!~/20/{print $0}' FS="," emp.csv

Output:

eno,ename,esal,eaddr
100,Sunny,1000,Mumbai
300,Chinny,3000,Hyderabad
400,Vinny,4000,Chennai
500,Pinny,5000,Mumbai

Key Notes

AWK treats every file as a tabular file by default.
Use FS to specify the field separator (default is whitespace).
Search strings can be applied globally or to specific fields using conditional expressions.

Match Total Field Value

Match any field containing 2000:
```
awk '/2000/{print $0}' FS="," emp.csv
```

Match if the 3rd field contains 2000:

awk '$3~/2000/{print $0}' FS="," emp.csv

Match if the 3rd field value is exactly 2000:
```
awk '$3==2000{print $0}' FS="," emp.csv
```

Match if the 4th field value is exactly Hyderabad:

awk '$4=="Hyderabad"{print $0}' FS="," emp.csv

Increment Salary by 500 Where Salary is Less Than 3000

Print records where salary is less than 3000:

awk -F "," '{if($3<3000) print $0}' emp.csv

Increment salary by 500 where salary is less than 3000:

awk -F "," '{if($3<3000) {$3=$3+500;print $0}}' emp.csv

Count Employees with Salary Greater Than 3000

Command:

awk -F "," 'BEGIN{c=0}NR!=1{if($3>3000){c=c+1;print $0;}}END{print "The Total Number of Employees where salary > 3000 :" c}' emp.csv

Another Way to Count Employees

AWK Code File (x.txt):

BEGIN {
 FS=",";
 c=0;
}
NR!=1 {
 if($3>3000) {
   c=c+1;
   print $0;
 }
}
END {
 print "The Total Number of Employees where salary > 3000 :" c;
}

Command:

awk -f x.txt emp.csv

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