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Full Discussion: Linux shell programming performance issue
Top Forums Shell Programming and Scripting Linux shell programming performance issue Post 302915099 by RudiC on Sunday 31st of August 2014 04:00:15 PM
Old 08-31-2014
You don't need awk (or similar) to improve the performance of your script. Just by the look on it, it can be seen that you run six commands (= six new processes) in the inner loop, times 50 for the lines in file 2, times millions for the lines in file1 (opening file2 millions times (even though buffered/cached)).

With your input data, and after cleaning out a few quirks in your code snippet, I find
Code:
time . XX
real    0m0.308s
user    0m0.192s
sys    0m0.119s

, while
Code:
time . YY
real    0m0.014s
user    0m0.012s
sys    0m0.000s

with YY being
Code:
while IFS='' read -r line
         do     while IFS=, read field1 field2
                        do      TMP=${line//$field1}
                                if [ $(( (${#line}- ${#TMP}) / ${#field1} )) -gt 1 ]
                                        then    sed  "s/"$field1"/"$field2"/2g"  <<<"$line" >> tmp.txt
                                        break
                                fi
                        done < file2
        done < file1
cat tmp.txt
TEXAS CALIFORNIA TX
DALLAS CALIFORNIA CALIFORNIA DA DA TEXAS

An even faster solution might be to use an array to hold file2's contents, and have the outer loop read file1, and an inner loop to iterate through the array doing the comparisons/modifications.

---------- Post updated at 22:00 ---------- Previous update was at 21:36 ----------

Modification using arrays; adapt to taste...:
Code:
unset i
while IFS=, read field1[++i] field2[i]; do : ; done < file2
while IFS='' read -r line
         do     for (( i=1; i<=${#field1[@]}; i++ ))
                        do      TMP=${line//${field1[$i]}}
                                if [ $(( (${#line}- ${#TMP}) / ${#field1[$i]} )) -gt 1 ]
                                        then    sed "s/"${field1[$i]}"/"${field2[$i]}"/2g"  <<<"$line" >> tmp.txt
                                        break
                                fi
                        done
        done < file1

Timing is similar to the first version; looks like the disk cache is quite powerful:
Code:
time . ZZ

real    0m0.015s
user    0m0.003s
sys    0m0.013s

 

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LEARN ABOUT CENTOS

times

TIMES(1P)						     POSIX Programmer's Manual							 TIMES(1P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       times - write process times

SYNOPSIS

       times

DESCRIPTION

       The times utility shall write the accumulated user and system times for the shell and for all of its  child  processes,	in  the  following
       POSIX locale format:

	      "%dm%fs %dm%fs
%dm%fs %dm%fs
", <shell user minutes>,
		  <shell user seconds>, <shell system minutes>,
		  <shell system seconds>, <children user minutes>,
		  <children user seconds>, <children system minutes>,
		  <children system seconds>

       The  four  pairs  of  times  shall  correspond to the members of the <sys/times.h> tms structure (defined in the Base Definitions volume of
       IEEE Std 1003.1-2001, Chapter 13, Headers) as returned by times(): tms_utime, tms_stime, tms_cutime, and tms_cstime, respectively.

OPTIONS

       None.

OPERANDS

       None.

STDIN

       Not used.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

       None.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       See the DESCRIPTION.

STDERR

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       Zero.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       None.

EXAMPLES

	      $ times
	      0m0.43s 0m1.11s
	      8m44.18s 1m43.23s

RATIONALE

       The times special built-in from the Single UNIX Specification is now required for all conforming shells.

FUTURE DIRECTIONS

       None.

SEE ALSO

       Special Built-In Utilities

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
       and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								 TIMES(1P)
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