join requires sorted input files. Each input file should be
sorted according to the key (=field/column number) used in
join. The recommended sorting option is ‘sort -k 1b,1’
(assuming the desired key is in the first column).
Typical usage:
$ sort -k 1b,1 file1 > file1.sorted $ sort -k 1b,1 file2 > file2.sorted $ join file1.sorted file2.sorted > file3
Normally, the sort order is that of the
collating sequence specified by the LC_COLLATE locale. Unless
the -t option is given, the sort comparison ignores blanks at
the start of the join field, as in sort -b. If the
--ignore-case option is given, the sort comparison ignores
the case of characters in the join field, as in sort -f:
$ sort -k 1bf,1 file1 > file1.sorted $ sort -k 1bf,1 file2 > file2.sorted $ join --ignore-case file1.sorted file2.sorted > file3
The sort and join commands should use consistent
locales and options if the output of sort is fed to
join. You can use a command like ‘sort -k 1b,1’ to
sort a file on its default join field, but if you select a non-default
locale, join field, separator, or comparison options, then you should
do so consistently between join and sort.
To avoid any locale-related issues, it is recommended to use the ‘C’ locale for both commands:
$ LC_ALL=C sort -k 1b,1 file1 > file1.sorted $ LC_ALL=C sort -k 1b,1 file2 > file2.sorted $ LC_ALL=C join file1.sorted file2.sorted > file3