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How To Print the Last 5 Fields in Awk

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Awk is a powerful text processing language that is often used for data extraction and reporting in a shell script. It is particularly useful for handling structured data such as text files and data streams. In this article, we will delve into how to print the last 5 fields in Awk, providing you with a comprehensive understanding of the process.

Quick Answer

To print the last 5 fields in Awk, you can use the NF variable along with various methods. One approach is to use a loop and printf to iterate through the fields and print them. Another method involves assigning an empty string to the first 5 fields and then printing the modified line. Additionally, you can use substr and index to extract a substring starting from the 6th field.

Understanding Awk

Before we dive into the specifics, it’s important to understand what Awk is and what it does. Awk is a domain-specific language designed for text processing and typically used as a data extraction and reporting tool. It’s a standard feature of most Unix-like operating systems.

Awk views a text file as records and fields. By default, a record is a line and fields are separated by whitespace (spaces and tabs). The variable NF represents the number of fields in the current record. Awk reads and processes input one line at a time, splitting each line into fields.

Printing the Last 5 Fields in Awk

To print the last 5 fields in Awk, you can utilize the NF variable. Here are a few methods to achieve this:

1. Using printf and a Loop

awk '{ for(i=NF-4; i<=NF; i++) printf $i" "; print "" }' input_file.txt

This command will loop through the fields starting from NF-4 (the 6th last field from the end) and print each field followed by a space. The print "" command is used to print a newline after each line.

2. Using Field Assignment

awk '{ for(i=1; i<=5; i++) $i=""; print }' input_file.txt

This command assigns an empty string to the first 5 fields, effectively removing them. Then, it prints the modified line, which contains only the last 5 fields.

3. Using substr and index

awk '{ print substr($0, index($0, $6)) }' input_file.txt

This command uses substr to extract a substring starting from the position of the 6th field. It relies on index to find the starting position of the 6th field within the line.

Alternatives to Awk

While Awk is a powerful tool, there are other methods to print the last 5 fields in a line. Here are a few alternatives:

1. Using cut Command

cut -d " " -f6-10 input_file.txt

The cut command can also be used to extract the desired fields. Here, we specify the delimiter as a space (-d " ") and select fields 6 to 10 (-f6-10).

2. Using Python

python -c 'import sys; fields=[" ".join(line.strip().split()[5:]) for line in sys.stdin]; print "\n".join(fields)' < input_file.txt

This Python one-liner splits each line into fields, discards the first 5 fields, and then joins the remaining fields with spaces. Finally, it prints the modified lines.

3. Using Ruby

ruby -ne 'print $_.split()[5..10].join(" "); print "\n"' < input_file.txt

This Ruby one-liner splits each line into an array of fields, selects fields 6 to 10, joins them with spaces, and then prints the modified lines.

4. Using Bash and xargs

cat input_file.txt | xargs -L 1 bash -c 'arr=($@); for i in $(seq 5 10); do printf "%s " ${arr[$i]}; done; echo' sh

This approach uses xargs to process each line and then uses a Bash loop to print fields 6 to 10.

Conclusion

In this article, we’ve explored how to print the last 5 fields in Awk, along with alternative methods using different commands and programming languages. With these tools and techniques, you can manipulate and process text data with greater flexibility and precision. Remember, the key to mastering Awk and similar tools is practice. So, don’t hesitate to experiment with these commands on your own.

What is Awk?

Awk is a powerful text processing language that is commonly used for data extraction and reporting in shell scripts. It is particularly useful for handling structured data such as text files and data streams.

How does Awk view a text file?

Awk views a text file as records and fields. By default, a record is a line and fields are separated by whitespace (spaces and tabs). The variable NF represents the number of fields in the current record. Awk reads and processes input one line at a time, splitting each line into fields.

What is the advantage of using Awk for text processing?

Awk provides a concise and powerful way to manipulate and process text data. It has built-in features for handling records and fields, making it well-suited for structured data. Awk is also highly customizable and can be easily integrated into shell scripts for automation and data extraction tasks.

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