coreutils: join invocation
8.3 ‘join’: Join lines on a common field
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‘join’ writes to standard output a line for each pair of input lines
that have identical join fields. Synopsis:
join [OPTION]... FILE1 FILE2
Either FILE1 or FILE2 (but not both) can be ‘-’, meaning standard
input. FILE1 and FILE2 should be sorted on the join fields.
$ cat file1
a 1
b 2
e 5
$ cat file2
a X
e Y
f Z
$ join file1 file2
a 1 X
e 5 Y
‘join’’s default behavior (when no options are given):
• 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.
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