How to Print Longest Line(s) in a File in Linux?

Introduction

Working with files is a common task for Linux users, and often, you may need to find longest line(s) in a file. While there are several ways to do this, there are a few simple methods that can make process quicker and more efficient. In this article, we will explore various methods for finding longest line(s) in a file in Linux.

Method 1: Using wc Command

The wc (word count) command is a useful tool that can be used to count number of lines, words, and characters in a file. However, it can also be used to find length of longest line in a file.

To use wc command to find longest line(s) in a file, follow these steps −

Step 1 − Open terminal and navigate to directory where file is located.
Step 2 − Type following command −

$ wc -L filename

This command will display length of longest line in file.

For example, let's say we have a file named "sample.txt" with following contents −

This is first line. This is second line. This is longest line in file. This is fourth line.

To find length of longest line in this file, we would enter following command −

$ wc -L sample.txt

The output would be −

32 sample.txt

This indicates that longest line in file is 32 characters long.

Method 2: Using grep Command

The grep command is another useful tool that can be used to find longest line(s) in a file. Grep searches for patterns in files and can be used to find longest line(s) in a file by searching for lines that match a certain pattern.

To use grep command to find longest line(s) in a file, follow these steps −

Step 1 − Open terminal and navigate to directory where file is located.
Step 2 − Type following command −

$ grep -n '.{80}' filename

This command will display all lines in file that are 80 characters or longer.

For example, let's say we have a file named "sample.txt" with following contents −

This is first line. This is second line. This is longest line in file. This is fourth line.

To find all lines in this file that are 20 characters or longer, we would enter following command −

$ grep -n '.{20}' sample.txt

The output would be −

3:This is longest line in file.

This indicates that only one line in file is longer than 20 characters.

Method 3: Using awk Command

The awk command is a powerful tool that can be used to process and manipulate text files. One of its many features is ability to find longest line(s) in a file.

To use awk command to find longest line(s) in a file, follow these steps −

Step 1 − Open terminal and navigate to directory where file is located.
Step 2 − Type following command −

$ awk '{ if ( length > L ) { L=length; X=$0 } } END { print X }' filename

This command will display longest line in file.

For example, let's say we have a file named "sample.txt" with following contents −

This is first line. This is second line. This is longest line in file. This is fourth line.

To find longest line in this file, we would enter following command −

$ awk '{ if ( length > L ) { L=length; X=$0 } } END { print X }

The output would be −

This is longest line in file.

This indicates that longest line in file is "This is longest line in file."

Method 4: Using sed Command

The sed command is a powerful tool that can be used to search for and replace text in a file. It can also be used to find longest line(s) in a file.

To use sed command to find longest line(s) in a file, follow these steps −

Step 1 − Open terminal and navigate to directory where file is located.
Step 2 − Type following command −

$ sed -n '/^.{100,}$/p' filename

This command will display all lines in file that are 100 characters or longer.

For example, let's say we have a file named "sample.txt" with following contents −

This is first line. This is second line. This is longest line in file. This is fourth line.

To find all lines in this file that are 30 characters or longer, we would enter following command −

$ sed -n '/^.{30,}$/p' sample.txt

The output would be −

This is longest line in file.

This indicates that only one line in file is longer than 30 characters.

Additional Methods for Finding Longest Line(s) in a File in Linux

Apart from above methods, there are some more ways to find longest line(s) in a file in Linux. In this section, we will explore some additional methods for accomplishing this task.

Method 5: Using Perl Command

The Perl command is a versatile tool that can be used for text processing tasks. One of its many features is ability to find longest line(s) in a file.

To use Perl command to find longest line(s) in a file, follow these steps −

Step 1 − Open terminal and navigate to directory where file is located.
Step 2 − Type following command −

$ perl -ne 'print length, " $_"' filename | sort -n | tail -1

This command will display length and content of longest line in file.

For example, let's say we have a file named "sample.txt" with following contents −

This is first line. This is second line. This is longest line in file. This is fourth line.

To find longest line in this file, we would enter following command −

$ perl -ne 'print length, " $_"' sample.txt | sort -n | tail -1

The output would be −

32 This is longest line in file.

This indicates that longest line in file is "This is longest line in file."

Method 6: Using Python Command

The Python command is a versatile tool that can be used for text processing tasks. One of its many features is ability to find longest line(s) in a file.

To use Python command to find longest line(s) in a file, follow these steps −

Step 1 − Open terminal and navigate to directory where file is located.
Step 2 − Type following command −

$ python -c "import sys; print max([len(line) for line in sys.stdin])" < filename

This command will display length of longest line in file.

For example, let's say we have a file named "sample.txt" with following contents −

This is first line. This is second line. This is longest line in file. This is fourth line.

To find longest line in this file, we would enter following command −

$ python -c "import sys; print max([len(line) for line in sys.stdin])" < sample.txt

The output would be −

This indicates that longest line in file is 32 characters long.

Method 7: Using R Command

The R command is a versatile tool that can be used for data analysis tasks. One of its many features is ability to find longest line(s) in a file.

To use R command to find longest line(s) in a file, follow these steps −

Step 1 − Open terminal and navigate to directory where file is located.
Step 2 − Type following command −

$ Rscript -e 'df <- readLines("filename"); max(nchar(df))'

This command will display length of longest line in file.

For example, let's say we have a file named "sample.txt" with following contents −

This is first line. This is second line. This is longest line in file. This is fourth line.

To find longest line in this file, we would enter following command −

$ Rscript -e 'df <- readLines("sample.txt"); max(nchar(df))'

The output would be −

This indicates that longest line in file is 32 characters long.

Conclusion

In conclusion, there are several methods for finding longest line(s) in a file in Linux. Using wc, grep, awk, and sed commands are all effective ways to accomplish this task. By using these tools, you can quickly and efficiently find longest line(s) in any file you are working with.