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Full Discussion: Speeding up shell script with grep
Top Forums Shell Programming and Scripting Speeding up shell script with grep Post 302994613 by RudiC on Saturday 25th of March 2017 06:20:42 AM
Old 03-25-2017
Using grep -f works, but with two files as large as indicated will take its (serious) time, and may eventually run out of memory. Try
Code:
sort master.csv new | uniq -d

, then use the resultant file in similar way (uniq -u) to extract unique values from either original file.
Comparison of both approaches on ~20k files:
Code:
time grep -ffile2 file1
real    0m0.352s
user    0m0.280s
sys     0m0.052s
time sort file[12] | uniq -d
real    0m0.037s
user    0m0.032s
sys     0m0.004s

EDIT: Times spent for two files with roughly 4E6 entries each, and about 1E6 lines overlap (on a two processor linux host):
Code:
time sort file[12] | uniq -d > f1
real    0m14.975s
user    0m27.048s
sys     0m0.792s
time sort file1 f1 | uniq -u > f2
real    0m9.331s
user    0m16.488s
sys     0m0.572s

Last edited by RudiC; 03-25-2017 at 01:22 PM..
 

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LEARN ABOUT MOJAVE

uniq

UNIQ(1) 						    BSD General Commands Manual 						   UNIQ(1)

NAME

     uniq -- report or filter out repeated lines in a file

SYNOPSIS

     uniq [-c | -d | -u] [-i] [-f num] [-s chars] [input_file [output_file]]

DESCRIPTION

     The uniq utility reads the specified input_file comparing adjacent lines, and writes a copy of each unique input line to the output_file.	If
     input_file is a single dash ('-') or absent, the standard input is read.  If output_file is absent, standard output is used for output.  The
     second and succeeding copies of identical adjacent input lines are not written.  Repeated lines in the input will not be detected if they are
     not adjacent, so it may be necessary to sort the files first.

     The following options are available:

     -c      Precede each output line with the count of the number of times the line occurred in the input, followed by a single space.

     -d      Only output lines that are repeated in the input.

     -f num  Ignore the first num fields in each input line when doing comparisons.  A field is a string of non-blank characters separated from
	     adjacent fields by blanks.  Field numbers are one based, i.e., the first field is field one.

     -s chars
	     Ignore the first chars characters in each input line when doing comparisons.  If specified in conjunction with the -f option, the
	     first chars characters after the first num fields will be ignored.  Character numbers are one based, i.e., the first character is
	     character one.

     -u      Only output lines that are not repeated in the input.

     -i      Case insensitive comparison of lines.

ENVIRONMENT

     The LANG, LC_ALL, LC_COLLATE and LC_CTYPE environment variables affect the execution of uniq as described in environ(7).

EXIT STATUS

     The uniq utility exits 0 on success, and >0 if an error occurs.

COMPATIBILITY

     The historic +number and -number options have been deprecated but are still supported in this implementation.

SEE ALSO

     sort(1)

STANDARDS

     The uniq utility conforms to IEEE Std 1003.1-2001 (``POSIX.1'') as amended by Cor. 1-2002.

HISTORY

     A uniq command appeared in Version 3 AT&T UNIX.

BSD
								 December 17, 2009							       BSD
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