intersection of two files according to the first column

Question

I have two files in file A, there are sequence_numbers in the other file B, there are many columns, and the first column is sequnce numbers, I want to get a files with all the lines in the B with the sequence numbers which are in the A how can I achieve this? thanks

like file A

1
3
8
9
20

file B

1 kfjk 3243424
2 fkdkf 23543592
3 iefjk 21493402
7 dlafdl 23435231
8 kfkdlkf 309834

Solution

You want join (1), I guess:

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.

[0 1075 12:50:10] ~/temp/sx % join A B
1 kfjk 3243424
3 iefjk 21493402
8 kfkdlkf 309834
join: file 1 is not in sorted order

OK, so apparently you need to combine this with sort (1) to sort by alpha value (not numerical value, so 20 < 3)

join <(sort A) <(sort B) works for me, but that looks weird and might be a zsh extension. There's no harm in doing

sort A > A.tmp; sort B > B.tmp; join A.tmp B.tmp

(As usual, check the man pages for pitfalls.)

Comments

[Gilles Quenot]

Better provide sample input & output.

[Will Vousden]

Process substitution (join <(sort A) <(sort B)) works just fine in bash :-)