Print Lines Between Two Patterns in Linux

Introduction

In Linux, command-line tools are essential for efficient text processing. One common task is extracting lines between two specific patterns in a text file. This article explores various methods to achieve this using command-line tools available in Linux.

Method 1: Using sed

sed, or stream editor, is a powerful tool for parsing and transforming text. To print lines between two patterns using sed, follow these steps:

sed -n '/start_pattern/,/end_pattern/p' filename

• Replace start_pattern and end_pattern with the actual patterns you’re looking for.
• -n suppresses automatic printing, and p at the end prints the matched lines.

Example:

sed -n '/BEGIN/,/END/p' example.txt

This command extracts lines between “BEGIN” and “END” in the “example.txt” file.

Method 2: Using awk

awk is a versatile programming language for pattern scanning and processing. To print lines between two patterns using awk:

awk '/start_pattern/,/end_pattern/' filename

Replace start_pattern and end_pattern with your specific patterns.

Example:

awk '/BEGIN/,/END/' example.txt

This command prints lines between “BEGIN” and “END” in the “example.txt” file.

Method 3: Using grep and awk

Combining grep and awk provides a concise solution. Here’s an example:

grep -n 'start_pattern' filename | awk -F: '{print $1}' | xargs -I {} sed -n '{}p' filename | sed -n '/start_pattern/,/end_pattern/p'

• grep -n finds the line numbers containing start_pattern.
• awk -F: extracts the line numbers.
• xargs -I {} passes each line number to the subsequent sed command.
• The final sed command extracts lines between the specified patterns.

Example:

grep -n 'BEGIN' example.txt | awk -F: '{print $1}' | xargs -I {} sed -n '{}p' example.txt | sed -n '/BEGIN/,/END/p'

This command extracts lines between “BEGIN” and “END” in the “example.txt” file using a combination of grep and sed.

Method 4: Using Perl

Perl is a powerful scripting language commonly used for text processing. Here’s an example of printing lines between two patterns using Perl:

perl -ne 'print if /start_pattern/../end_pattern/' filename

Replace start_pattern and end_pattern with your specific patterns.

Example:

perl -ne 'print if /BEGIN/../END/' example.txt

This command prints lines between “BEGIN” and “END” in the “example.txt” file using Perl.

Conclusion

Linux provides several powerful tools for text processing, and printing lines between two patterns is a common requirement. Depending on your preference and the complexity of your task, you can choose the method that best suits your needs. Whether it’s sed, awk, a combination of grep and awk, or Perl, these tools offer flexibility and efficiency in handling text data from the command line.