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Join lines on a common field, writes to standard output a line for each pair of input lines that have identical join fields.

      join [OPTION]... FILE1 FILE2


Either FILE1 or FILE2 (but not both) can be `-', meaning standard input. FILE1 and FILE2 should be already sorted in increasing textual order on the join fields, using the collating sequence specified by the `LC_COLLATE' locale.

Unless the `-t' option is given, the input should be sorted ignoring blanks at the start of the join field, as in `sort -b'. If the `--ignore-case' option is given, lines should be sorted without regard to the case of characters in the join field, as in `sort

The defaults are:
The join field is the first field in each line;
Fields in the input are separated by one or more blanks, with leading blanks on the line ignored;
Fields in the output are separated by a space;
Each output line consists of the join field, the remaining fields from FILE1, then the remaining fields from FILE2.


     Print a line for each unpairable line in file FILE-NUMBER (either
     `1' or `2'), in addition to the normal output.

     Replace those output fields that are missing in the input with

     Ignore differences in case when comparing keys.  With this option,
     the lines of the input files must be ordered in the same way.  Use
     `sort -f' to produce this ordering.

`-1 FIELD'
`-j1 FIELD'
     Join on field FIELD (a positive integer) of file 1.

`-2 FIELD'
`-j2 FIELD'
     Join on field FIELD (a positive integer) of file 2.

`-j FIELD'
     Equivalent to `-1 FIELD -2 FIELD'.

`-o FIELD-LIST...'
     Construct each output line according to the format in FIELD-LIST.
     Each element in FIELD-LIST is either the single character `0' or
     has the form M.N where the file number, M, is `1' or `2' and N is
     a positive field number.

     A field specification of `0' denotes the join field.  In most
     cases, the functionality of the `0' field spec may be reproduced
     using the explicit M.N that corresponds to the join field.
     However, when printing unpairable lines (using either of the `-a'
     or `-v' options), there is no way to specify the join field using
     M.N in FIELD-LIST if there are unpairable lines in both files.  To
     give `join' that functionality, POSIX invented the `0' field
     specification notation.

     The elements in FIELD-LIST are separated by commas or blanks.
     Multiple FIELD-LIST arguments can be given after a single `-o'
     option; the values of all lists given with `-o' are concatenated
     together.  All output lines - including those printed because of
     any -a or -v option - are subject to the specified FIELD-LIST.

`-t CHAR'
     Use character CHAR as the input and output field separator.

     Print a line for each unpairable line in file FILE-NUMBER (either
     `1' or `2'), instead of the normal output.

A nation is not in danger of financial disaster merely because it owes itself money" - Andrew William Mellon

Related commands:

csplit - Split a file into context-determined pieces
cut - Divide a file into several parts
fmt - Reformat paragraph text
fold - Wrap input lines to fit in specified width
head - Output the first part of file(s)
paste - Merge lines of files
split - Split a file into fixed-size pieces
tail - Output the last part of files