command join

info

1. join the lines of two files which share a common field of data

2. default join field is the first

3. delimited by whitespace

4. file1 and file2 must be sorted on the join fields

options

1. -tchar use char as input and output field separator

2. -1 field join on this field of file 1

3. -2 field join on this field of file 2

demo

1. computerhope demo

   1. test data

       $ pico file1.txt
       1 India
       2 US
       3 Ireland
       4 UK
       5 Canada
      
       $ pico file2.txt
       1 NewDelhi
       2 Washington
       3 Dublin
       4 London
       5 Toronto
      

   2. join the contents

       $ join file1.txt file2.txt
       1 India NewDelhi
       2 US Washington
       3 Ireland Dublin
       4 UK London
       5 Canada Toronto
      

   3. redirect to a file

       $ join file1.txt file2.txt > file3.txt
      

2. albany edu demo

   1. test data

       $ pico file1.txt
       1 abc
       2 lmn
       3 pqr
      
       $ pico file2.txt
       1 abc
       3 lmn
       9 opq
      

   2. join with 1st column

       $ join file1.txt file2.txt
       1 abc abc
       3 pqr lmn
      

   3. join with 2ed column inner join

       $ join -1 2 -2 2 file1.txt file2.txt
      

   4. include all records from 1st file left outer join

       $ join -a1 -1 2 -2 2 file1.txt file2.txt
       abc 1 1
       lmn 2 3
       pqr 3
      

   5. also include all records from 2ed file full outer join

       $ join -a1 -a2 -1 2 -2 2 file1.txt file2.txt
       abc 1 1
       lmn 2 3
       opq 9
       pqr 3
      

   6. format the output

       # `-o` option
       # `0` display the join field
              
       # `x.y` display `y` field from the `x` file
       # `2.1` means display 1st field from 2ed file
      
       # `-e "0"` replace missing data fields
       # with whatever is in-between the quotes
       # in this case a `0`
       $ join -a1 -a2 -1 2 -2 2 -o 0 1.1 2.1 -e "X" file1.txt file2.txt
       abc 1 1
       lmn 2 3
       opq X 9
       pqr 3 X