Shells, forks, subprocesses... oh my Post: 302993535

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Top Forums Shell Programming and Scripting Shells, forks, subprocesses... oh my Post 302993535 by Corona688 on Friday 10th of March 2017 05:54:35 PM

03-10-2017

Registered User

sed, bash, perl, awk, find, grep are all processes. A subshell is a process. A fork is a fork is a fork.

Whether any of these are faster or slower than other ways to solve your problem, really depends on your problem, and the algorithm you use to solve it. So "one solution to solve everything, forever" may be out the window.

There's some cardinal sins to avoid:

Don't reprocess the same file repeatedly. You can almost always do everything in one pass that you could do in two.
Don't launch whole processes to process tiny amounts of data. echo "a b c" | awk '{ print $1 }' is a tragic waste, this is when shell builtins would be thousands of times more efficient.
Running your innermost loop in the shell will be slow. A while read loop line by line over a file will be slower than awk '{ something }' filename. Shell is for the high level things, not the nitty gritty bulk work. This is when externals would be thousands of times more efficient.
If you're doing cat | awk | sed | cut | tr | kitchen | sink, put it all in one awk. awk is a programming language which is capable of replacing all of these with some near-trivial code, and one awk call will be faster than ten anything else.
Useless Use of Cat. Don't do that. Nothing needs a cat | in front of it to read a file.

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igawk

IGAWK(1)							 Utility Commands							  IGAWK(1)

NAME

       igawk - gawk with include files

SYNOPSIS

       igawk [ all gawk options ] -f program-file [ -- ] file ...
       igawk [ all gawk options ] [ -- ] program-text file ...

DESCRIPTION

       Igawk is a simple shell script that adds the ability to have ``include files'' to gawk(1).

       AWK programs for igawk are the same as for gawk, except that, in addition, you may have lines like

	      @include getopt.awk

       in your program to include the file getopt.awk from either the current directory or one of the other directories in the search path.

OPTIONS

       See gawk(1) for a full description of the AWK language and the options that gawk supports.

EXAMPLES

       cat << EOF > test.awk
       @include getopt.awk

       BEGIN {
	    while (getopt(ARGC, ARGV, "am:q") != -1)
		 ...
       }
       EOF

       igawk -f test.awk

SEE ALSO

       gawk(1)

       Effective AWK Programming, Edition 1.0, published by the Free Software Foundation, 1995.

AUTHOR

       Arnold Robbins (arnold@skeeve.com).

Free Software Foundation					    Nov 3 1999								  IGAWK(1)