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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 REDHAT

unix2dos

unix2dos(1)						      General Commands Manual						       unix2dos(1)

NAME

       unix2dos - UNIX to DOS text file format converter

SYNOPSYS

       unix2dos [options] [-c convmode] [-o file ...] [-n infile outfile ...]

       Options:

       [-hkqV] [--help] [--keepdate] [--quiet] [--version]

DESCRIPTION

       This manual page documents unix2dos, the program that converts text files in UNIX format to DOS format.

OPTIONS

       The following options are available:

       -h --help
	      Print online help.

       -k --keepdate
	      Keep the date stamp of output file same as input file.

       -q --quiet
	      Quiet mode. Suppress all warning and messages.

       -V --version
	      Prints version information.

       -c --convmode convmode
	      Sets conversion mode. Simulates unix2dos under SunOS.

       -o --oldfile file ...
	      Old file mode. Convert the file and write output to it. The program default to run in this mode. Wildcard names may be used.

       -n --newfile infile outfile ...
	      New  file  mode.	Convert the infile and write output to outfile. File names must be given in pairs and wildcard names should NOT be
	      used or you WILL lost your files.

EXAMPLES

       Get input from stdin and write output to stdout.

	      unix2dos

       Convert and replace a.txt. Convert and replace b.txt.

	      unix2dos a.txt b.txt

	      unix2dos -o a.txt b.txt

       Convert and replace a.txt in ASCII conversion mode.  Convert and replace b.txt in ISO conversion mode.

	      unix2dos a.txt -c iso b.txt

	      unix2dos -c ascii a.txt -c iso b.txt

       Convert and replace a.txt while keeping original date stamp.

	      unix2dos -k a.txt

	      unix2dos -k -o a.txt

       Convert a.txt and write to e.txt.

	      unix2dos -n a.txt e.txt

       Convert a.txt and write to e.txt, keep date stamp of e.txt same as a.txt.

	      unix2dos -k -n a.txt e.txt

       Convert and replace a.txt. Convert b.txt and write to e.txt.

	      unix2dos a.txt -n b.txt e.txt

	      unix2dos -o a.txt -n b.txt e.txt

       Convert c.txt and write to e.txt. Convert and replace a.txt.  Convert and replace b.txt. Convert d.txt and write to f.txt.

	      unix2dos -n c.txt e.txt -o a.txt b.txt -n d.txt f.txt

DIAGNOSTICS

BUGS

       The program does not work properly under MSDOS in stdio processing mode.  If you know why is that so, please tell me.

AUTHOR

       Benjamin Lin - ( blin@socs.uts.edu.au )

MISCELLANY

       Tested environment:

	      Linux 1.2.0 with GNU C 2.5.8

	      SunOS 4.1.3 with GNU C 2.6.3

	      MS-DOS 6.20 with Borland C++ 4.02

       Suggestions and bug reports are welcome.

SEE ALSO

       dos2unix(1)

1995.03.31							   unix2dos v2.2						       unix2dos(1)
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