$ curl cheat.sh/

# join
# Join lines of two sorted files on a common field.
# More information: <https://www.gnu.org/software/coreutils/join>.

# Join two files on the first (default) field:
join file1 file2

# Join two files using a comma (instead of a space) as the field separator:
join -t ',' file1 file2

# Join field3 of file1 with field1 of file2:
join -1 3 -2 1 file1 file2

# Produce a line for each unpairable line for file1:
join -a 1 file1 file2

# Join a file from `stdin`:
cat path/to/file1 | join - path/to/file2

$

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