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Performance Issue for a file search command

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# 1  
Performance Issue for a file search command

Hi All,

This query is regarding performance improvement of a command.

I have a list of IDs in a file (say file1 with single ID column) and file2 has the data rows.

I need to get the IDs from file1 and search in file2, matching rows from file2 should be written to a file3.

For this scenario I have been using below command-

 for ID in `cat file1`; do grep $ID file2; done > file3

The command I am using is super slow. Can someone please let me know how can I improve the performance here.

Thanks in advance,
# 2  
From man grep:
       -f FILE, --file=FILE
              Obtain patterns  from  FILE,  one  per  line.   The  empty  file
              contains zero patterns, and therefore matches nothing.

grep -f file1 file2 > file3

This User Gave Thanks to Corona688 For This Post:
# 3  
Thank you for your reply @Corona688. But I see the grep command mentioned by you is also running very slow. I am working with files having millions of records.

Let me know if any other way to improve the search.
# 4  
How big is file1? If it's larger than available memory, it will of course be slow.
# 5  
Hi Corona688,

grep -F -f file1 file2 > file3

The above code (added -F) worked really fast for me. I could complete search for a file with 1.5 million records in 5-6 seconds.

Really appreciate for your response.

This User Gave Thanks to Tanu For This Post:

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