82.Processing_Tabular_Data.md

awk command for processing tabular data

1. Field Representations:

   • $0: Represents the entire line or record.
   • $1: Represents the first column.
   • $2: Represents the second column.
   • $3: Represents the third column, and so on.

2. Default Separator:

   • By default, awk treats tab as the field separator.
   • For other separators (e.g., , in CSV files), use the -F option or FS variable.

3. Processing Commands:

   • To print specific fields or the entire line, use print with field variables.
   • Logical and relational operators with the NR variable (row number) allow row-based operations.

1. Printing Specific Fields

awk '{print $1}' emp.txt

Output:

eno
100
200
300
400
500

2. Printing First and Third Columns

awk '{print $1 " " $3}' emp.txt

Output:

eno esal
100 1000
200 2000
300 3000
400 4000
500 5000

3. Processing CSV Files

Using , as the separator:

awk -F "," '{print $2 " " $4}' emp.csv

Output:

ename eaddr
Durga Mumbai
Bunny Hyderabad
Chinny Hyderabad
Vinny Chennai
Pinny Mumbai

4. Displaying Content Without the Header

awk 'NR != 1 {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

Relational Operators with NR

• NR (Number of Records) is useful for filtering specific rows.

• Examples:

  awk 'NR==2 || NR==4 {print $0}' FS="," emp.csv

  Output:

  200,Bunny,2000,Hyderabad
  400,Vinny,4000,Chennai
  

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

  Output:

  300,Chinny,3000,Hyderabad
  400,Vinny,4000,Chennai
  

Handling Single-Column Data

File: xy.txt

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

Commands:

1. Entire Line:

   awk '{print $0}' xy.txt

   Output:

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

2. First Column:

   awk '{print $1}' xy.txt

   Output:

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

3. Second Column:

   awk '{print $2}' xy.txt

   Output: (Nothing is printed because there is no second column.)

Key Notes

• The default separator for awk is tab. If you need to work with another separator (e.g., commas), you must specify it using -F or FS.
• awk assumes all input files are tabular.
• Relational operators (!=, <, >, <=, etc.) work effectively with the NR variable for filtering rows.