shell join详解

Usage: join [OPTION]... FILE1 FILE2
For each pair of input lines with identical join fields, write a line to
standard output.  The default join field is the first, delimited
by whitespace.  When FILE1 or FILE2 (not both) is -, read standard input.

  -a FILENUM        print unpairable lines coming from file FILENUM, where
                      FILENUM is 1 or 2, corresponding to FILE1 or FILE2
  -e EMPTY          replace missing input fields with EMPTY
  -i, --ignore-case ignore differences in case when comparing fields
  -j FIELD          equivalent to `-1 FIELD -2 FIELD‘
  -o FORMAT         obey FORMAT while constructing output line
  -t CHAR           use CHAR as input and output field separator
  -v FILENUM        like -a FILENUM, but suppress joined output lines
  -1 FIELD          join on this FIELD of file 1
  -2 FIELD          join on this FIELD of file 2
      --help     display this help and exit
      --version  output version information and exit

Unless -t CHAR is given, leading blanks separate fields and are ignored,
else fields are separated by CHAR.  Any FIELD is a field number counted
from 1.  FORMAT is one or more comma or blank separated specifications,
each being `FILENUM.FIELD‘ or `0‘.  Default FORMAT outputs the join field,
the remaining fields from FILE1, the remaining fields from FILE2, all
separated by CHAR.

Important: FILE1 and FILE2 must be sorted on the join fields.

Report bugs to <bug-coreutils@gnu.org>.

$ cat A.txt

1 abc 20
2 ccc 22
3 sed 11
4 xxx 23

$ cat B.txt

1 h 0
2 x 2
3 b 3
5 s 3

$ join A.txt B.txt

1 abc 20 h 0
2 ccc 22 x 2
3 sed 11 b 3

$ join -a1 A.txt B.txt
1 abc 20 h 0
2 ccc 22 x 2
3 sed 11 b 3
2 xxx 23

$ join -a1 -a2 A.txt B.txt
1 abc 20 h 0
2 ccc 22 x 2
3 sed 11 b 3
2 xxx 23
5 s 3

$ join -a1 -a2 -e"_" -o‘1.1 1.2 1.3 2.1 2.2 2.3‘ A.txt B.txt
1 abc 20 1 h 0
2 ccc 22 2 x 2
3 sed 11 3 b 3
2 xxx 23 _ _ _
_ _ _ 5 s 3

join -v1 A.txt B.txt
2 xxx 23