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    <p>some python to the rescue.</p> <p>I created two text-files using the following snippet:</p> <pre><code>#!/usr/bin/env python import random import string N=2000000 for i in range(N): s = ''.join(random.choice(string.ascii_uppercase + string.digits) for x in range(40)) print s + '|4|2|20705|9550|21419' </code></pre> <p>one 300k and one 2M lines This gives me the following files:</p> <pre><code>$ ll -rwxr-xr-x 1 210 Jun 11 22:29 gen_random_string.py* -rw-rw-r-- 1 119M Jun 11 22:31 large.txt -rw-rw-r-- 1 18M Jun 11 22:29 small.txt </code></pre> <p>Then I appended a line from small.txt to the end of large.txt so that I had a matching pattern</p> <p>Then some more python:</p> <pre><code>#!/usr/bin/env python target = {} with open("large.txt") as fd: for line in fd: target[line.split('|')[0]] = line.strip() with open("small.txt") as fd: for line in fd: if line.split('|')[0] in target: print target[line.split('|')[0]] </code></pre> <p>Some timings:</p> <pre><code>$ time ./comp.py 3A8DW2UUJO3FYTE8C5ESE25IC9GWAEJLJS2N9CBL|4|2|20705|9550|21419 real 0m2.574s user 0m2.400s sys 0m0.168s $ time awk -F"|" 'NR==FNR{a[$1]=$2;next}{if (a[$1]) print}' small.txt large.txt 3A8DW2UUJO3FYTE8C5ESE25IC9GWAEJLJS2N9CBL|4|2|20705|9550|21419 real 0m4.380s user 0m4.248s sys 0m0.124s </code></pre> <p>Update:</p> <p>To conserve memory, do the dictionary-lookup the other way</p> <pre><code>#!/usr/bin/env python target = {} with open("small.txt") as fd: for line in fd: target[line.split('|')[0]] = line.strip() with open("large.txt") as fd: for line in fd: if line.split('|')[0] in target: print line.strip() </code></pre>
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    1. POoptimizing this script to match lines of one txt file with another
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    1. CO@FredrikPhil thanks alot much appreciated ... I am excepting Ansgar Wiechers answer simply because on my ec2 instance I get a memory error running your python script (there's just not enough ram) I ran it on my desktop though and it does work! So I will be keeping it in my back pocket for when I do scale up to a larger instance as I approach launching my application. Thanks again! +1
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    2. COGlad I could help. It was an interesting task. Normally you'd use the approach outlined in http://mywiki.wooledge.org/BashFAQ/036 This one was different.
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    3. CO@brendanmorrison - BTW updated python-code to reduce memory needed by a factor of almost seven :-)
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