Linux join Guide

Linux join Guide

Complete beginner-friendly guide to join on Linux, covering Arch Linux, CachyOS, and other distributions including joining files, database-like operations, and file merging.

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Table of Contents

1. Understanding join
2. join Basics
3. Joining Files
4. Field Selection
5. Troubleshooting

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Understanding join

What is join?

join joins lines from two files on common field.

Uses:

• Join files: Merge files on common field
• Database operations: SQL-like joins
• Data merging: Combine data sets
• File operations: Merge related data

Why it matters:

• Data processing: Merge related data
• Database-like: SQL join operations
• File merging: Combine files

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join Basics

Join Files

Basic usage:

# Join on first field (default)
join file1.txt file2.txt

# Files must be sorted on join field

Join Field

Specify field:

# Join on field 2
join -1 2 -2 2 file1.txt file2.txt

# -1 2 = file1 field 2
# -2 2 = file2 field 2

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Joining Files

Output Format

Default output:

# Output: join_field file1_other_fields file2_other_fields
join file1.txt file2.txt

Custom Format

Format output:

# Format output
join -o 1.1,2.2 file1.txt file2.txt

# -o = output format

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Field Selection

Multiple Fields

Select fields:

# Select specific fields
join -o 1.1,1.2,2.3 file1.txt file2.txt

# file1 field1, file1 field2, file2 field3

Missing Fields

Handle missing:

# Include unmatched lines
join -a 1 file1.txt file2.txt

# -a = include unmatched from file1

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Troubleshooting

Files Not Sorted

Sort first:

# Sort on join field
sort -k1 file1.txt > file1.sorted.txt
sort -k1 file2.txt > file2.sorted.txt
join file1.sorted.txt file2.sorted.txt

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Summary

This guide covered join usage, file joining, and data merging for Arch Linux, CachyOS, and other distributions.

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Next Steps

• sort Guide - Sorting files
• cut Guide - Field extraction
• comm Guide - File comparison
• join Documentation: man join

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This guide covers Arch Linux, CachyOS, and other Linux distributions. For distribution-specific details, refer to your distribution's documentation.