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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LEARN ABOUT DEBIAN

dpkg-www

DPKG-WWW(1)						      General Commands Manual						       DPKG-WWW(1)

NAME

       dpkg-www - program to remotely open a WWW Debian package browser

SYNOPSIS

       dpkg-www [-s|--stdout] [-h|--host host] [query]

DESCRIPTION

       dpkg-www is used to remotely control a WEB browser and open a dpkg URL on the local host from an interactive shell or script.

       If  the	command  is invoked while running under X-window the script will try to find an installed X browser to open the specified URL.	If
       not running under X it will try to use a text browser instead.

       If Netscape is found and a Netscape instance is already running it will be asked to open the dpkg URL on localhost with the optional  query
       supplied on the command line.  If there is no browser running, it will start automatically a new one.

       The  functionality  provided  by this program is identical to running a web browser with the -remote openURL(http://localhost/cgi-bin/dpkg)
       argument or opening the same URL from within the browser.

       dpkg-www-installer is an helper application which can configured in the WWW browser for	web  installation.  It	should	never  be  invoked
       directly by the user.

OPTIONS

       -s, --stdout
	      Redirect output to stdout. Requires one of the text browsers (lynx, lynx-ssl or links) installed.

       -h, --host host
	      Send the query to a remote host, where dpkg-www must be installed.

       query  Specifies  an  optional  package name, an absolute pathname or a query argument which is passed to the dpkg cgi-bin. See dpkg-www(8)
	      for more information about the use of the cgi.

FILES

       /etc/dpkg-www.conf

       ~/.dpkg-www
	      Configuration files for dpkg-www. It is not necessary for these files to exist, there are sensible defaults for everything, but  you
	      can specify your preferred www browser with the DPKG_WWW_BROWSER variable, for example: DPKG_WWW_BROWSER=mozilla

EXAMPLES

       dpkg-www
	      This would open a dpkg URL on localhost listing all the installed packages.

       dpkg-www bash
	      This would open a dpkg URL asking info on the bash package.

       dpkg-www -h pisolo bash
	      This would open a dpkg URL asking info on the bash package on host pisolo.

       dpkg-www 'dpkg*'
	      This would open a dpkg URL listing all packages matching dpkg*.

       dpkg-www /bin/bash
	      This would open a dpkg URL asking info on the package(s) owning the file /bin/bash .

       dpkg-www depends=svgalib
	      This would open a dpkg URL listing all packages depending on svgalib.

       dpkg-www --stdout depends=awk | grep ^ii
	      This would list on stdout all packages depending on awk and grep all lines of installed packages.

SEE ALSO

       dpkg(8), dpkg-www(8)

AUTHOR

       Massimo Dal Zotto <dz@debian.org>.
       Bugs should be reported via the normal Debian bug reporting system.

LICENCE

       dpkg-www is licensed under the GNU General Public License version 2.

								 September 1, 2004						       DPKG-WWW(1)