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📛 NAME

join — join lines of two files on a common field

🚀 Quick Reference

🔍 Use Case	⌨️ Command	📝 Description
Inner join	join file1 file2	Default: join on first field, output matching lines
Left outer join	join -a 1 file1 file2	Include all lines from file1 even if unmatched
Right outer join	join -a 2 file1 file2	Include all lines from file2
Full outer join	join -a 1 -a 2 file1 file2	Combine both -a flags
Specify join field	join -1 2 -2 3 file1 file2	Field 2 of file1 with field 3 of file2
Different delimiter	join -t ':' file1 file2	Use colon as field separator
Case‑insensitive	join -i file1 file2	Ignore case differences in join fields
Only unpairable lines	join -v 1 file1 file2	Show lines from file1 with no match
Custom output format	join -o 1.2,2.3 file1 file2	Output field 2 of file1 and field 3 of file2
Replace missing fields	join -a 1 -e N/A file1 file2	Fill empty fields with “N/A”

📋 SYNOPSIS

join [OPTION]... FILE1 FILE2

📖 Description

For each pair of input lines with identical join fields, write a line to standard output. The default join field is the first, delimited by blanks.

When FILE1 or FILE2 (not both) is -, read standard input.

🔹 -a FILENUM

also print unpairable lines from file FILENUM, where FILENUM is 1 or 2, corresponding to FILE1 or FILE2

🔹 -e EMPTY

replace missing input fields with EMPTY

🔹 -i, --ignore-case

ignore differences in case when comparing fields

🔹 -j FIELD

equivalent to -1 FIELD -2 FIELD

🔹 -o FORMAT

obey FORMAT while constructing output line

🔹 -t CHAR

use CHAR as input and output field separator

🔹 -v FILENUM

like -a FILENUM, but suppress joined output lines

🔹 -1 FIELD

join on this FIELD of file 1

🔹 -2 FIELD

join on this FIELD of file 2

🔹 --check-order

check that the input is correctly sorted, even if all input lines are pairable

🔹 --nocheck-order

do not check that the input is correctly sorted

🔹 --header

treat the first line in each file as field headers, print them without trying to pair them

🔹 -z, --zero-terminated

line delimiter is NUL, not newline

🔹 --help

display this help and exit

🔹 --version

output version information and exit

Unless -t CHAR is given, leading blanks separate fields and are ignored, else fields are separated by CHAR. Any FIELD is a field number counted from 1. FORMAT is one or more comma or blank separated specifications, each being FILENUM.FIELD or 0. Default FORMAT outputs the join field, the remaining fields from FILE1, the remaining fields from FILE2, all separated by CHAR. If FORMAT is the keyword auto, then the first line of each file determines the number of fields output for each line.

Important: FILE1 and FILE2 must be sorted on the join fields. E.g., use sort -k 1b,1 if join has no options, or use join -t '' if sort has no options. Note, comparisons honor the rules specified by LC_COLLATE. If the input is not sorted and some lines cannot be joined, a warning message will be given.

👤 Author

Written by Mike Haertel.

🐛 Reporting Bugs

GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Report any translation bugs to <https://translationproject.org/team/>

©️ Copyright

Copyright © 2020 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

📚 See Also

comm(1), uniq(1)

Full documentation <https://www.gnu.org/software/coreutils/join>
or available locally via: info '(coreutils) join invocation'

📛 NAME 🚀 Quick Reference 📋 SYNOPSIS 📖 Description 👤 Author 🐛 Reporting Bugs ©️ Copyright 📚 See Also