比较两个文件diff awk else

Question

Could you please quickly help me with this? I have two files with 1 columns in each file. I need to compare fileA to fileB and find out which items in FileA are already in FILEB and print them out to another file.So basically like to find out which name they have in common.

so I have something like this

FILEA

MATT.1
HANNA.1
OTTOO.2
MARK.2
SAM.3

FILEB

SAM.3
MATT.1
JEFF.6
ALI.8

The result file should be

SAM.3
MATT.1

I was thinking of writing a shell script cat one file and do a line by line comparison, but there must a better and easier way to do this using one of many commands. Can you help?

Regards

Answer 1

This is a job for comm . The input files need to be sorted though

comm -12 <(sort file1) <(sort file2)

will give you the common lines.

An awk answer:

awk 'NR==FNR {f[$0]=1; next} $0 in f' fileb filea

Put the smaller file as the first argument to limit the amount of memory required.

Answer 2

This looks returns lines from filea that match any line in fileb:

$ grep -Ff fileb filea
MATT.1
SAM.3

-F tells grep to look for fixed patterns, not regular expressions.

-f tells grep to get the list of patterns from a file which, in this case, is fileb .

More options

We can make the matches more restrictive with these options:

-w would tell grep to match only whole words.

-x would tell grep to match only whole lines.