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Issue when using egrep to extract strings (too many strings)

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# 1  
Issue when using egrep to extract strings (too many strings)

Dear all,
I have a data like below (n of rows=400,000) and I want to extract the rows with certain strings. I use code below. It works if there is not too many strings for example n of strings <5000. while I have 90,000 strings to extract. If I use the egrep code below, I will get error:

 /usr/bin/egrep: Argument list too long

data example:
 ILMN_167228 9.523 1.599 8.518
 ILMN_168228 8.823 2.599 8.518
 ILMN_169228 8.023 3.599 8.518
 ILMN_1751228 8.423 4.599 8.518
 ILMN_7751228 8.323 5.599 8.518
 ILMN_1881228 8.223 8.599 8.518


code example:
 egrep '(ILMN_2258774|ILMN_1700477|...|ILMN_1805992)' test1>test2

I got error since I have too many number of strings (n=80,000) to extract.

 /usr/bin/egrep: Argument list too long

any one know how to fix it or any other way that can handle my request? Thank you.
# 2  
You could try putting those strings in a file, like so:


Then you can extract like so:
grep -f stringfile test1>test2

For accuracy it would be better to use anchoring, by using a single space after each of the strings (ILMN_ is unique enough so the does not need to be a ^ in front) , to avoid possible false positives because of substring matches, unless all strings have the same length:


On Solaris use /usr/xpg4/bin/grep

Last edited by Scrutinizer; 04-20-2016 at 08:23 PM..
This User Gave Thanks to Scrutinizer For This Post:
# 3  
There might be a performance problem also, because grep might do the comparisons one after the other, like a loop would do, for each line. Anchoring makes each comparison only a little faster.
If you have a plain stringlist file without RE wildcards and without spaces, while your main file is space separated and your strings should match the first field, then a hash is much faster. With awk
awk 'NR==FNR {A[$1]; next} ($1 in A)' stringfile test1>test2

Last edited by MadeInGermany; 04-21-2016 at 03:43 AM..
This User Gave Thanks to MadeInGermany For This Post:
# 4  
Thank you guys. I tried the code below and it works.
awk 'NR==FNR {A[$1]; next} ($1 in A)' stringfile test1>test2


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