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Full Discussion: Conversion of Perl Script to Shell Script..
Top Forums Shell Programming and Scripting Conversion of Perl Script to Shell Script.. Post 302929470 by Corona688 on Monday 22nd of December 2014 02:14:53 AM
Old 12-22-2014
Quote:
Originally Posted by ongoto
@ Corona688

I see. Well then, this is me, back pedaling. I have no doubt what you are saying is accurate. And from that I gather that Perl is running on top of the shell rather than independent of it. That I didn't realize.
Oh, it is independent of it.

system() is not. system() means "run this command in a shell". it kind has to use a shell, because that's what it means.

So, to run external commands, it generally has to use a shell.

Perl built-ins and perl modules, on the other hand, are native. (Unless they use system() for something.)
Quote:
I'm wondering now if the same is true for Python?
Quite probably. Remember, that's what system() means -- "run this command in a native shell".

Also remember that not using a shell to handle it means you have to handle splitting, pipes, and path lookups yourself. That's all the shell's job traditionally. So it's either do all the hard work yourself, build at least half of a good shell into your language, or hand the job off to the shell.

As for python's overhead in general, one might wonder, how many files does it take to do absolutely nothing? The answer is interesting:

Code:
~ $ strace bash /dev/null 2>&1 | grep -c open
8
~ $ strace perl /dev/null 2>&1 | grep -c open
8
~ $ strace awk '{}' /dev/null 2>&1 | grep -c open
5
~ $ strace python /dev/null 2>&1 | grep -c open
53
~ $

 

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LEARN ABOUT MOJAVE

platform::shell

platform::shell(n)					       Tcl Bundled Packages						platform::shell(n)

__________________________________________________________________________________________________________________________________________________

NAME

       platform::shell - System identification support code and utilities

SYNOPSIS

       package require platform::shell ?1.1.4?

       platform::shell::generic shell
       platform::shell::identify shell
       platform::shell::platform shell
_________________________________________________________________

DESCRIPTION

       The platform::shell package provides several utility commands useful for the identification of the architecture of a specific Tcl shell.

       This  package  allows the identification of the architecture of a specific Tcl shell different from the shell running the package. The only
       requirement is that the other shell (identified by its path), is actually executable on the current machine.

       While for most platform this means that the architecture of the interrogated shell is identical to the architecture of  the  running  shell
       this  is  not generally true. A counter example are all platforms which have 32 and 64 bit variants and where a 64bit system is able to run
       32bit code. For these running and interrogated shell may have different 32/64 bit settings and thus different identifiers.

       For applications like a code repository it is important to identify the architecture of the shell which will  actually  run  the  installed
       packages, versus the architecture of the shell running the repository software.

COMMANDS

       platform::shell::identify shell
	      This command does the same identification as platform::identify, for the specified Tcl shell, in contrast to the running shell.

       platform::shell::generic shell
	      This command does the same identification as platform::generic, for the specified Tcl shell, in contrast to the running shell.

       platform::shell::platform shell
	      This command returns the contents of tcl_platform(platform) for the specified Tcl shell.

KEYWORDS

       operating system, cpu architecture, platform, architecture

platform::shell 						       1.1.4							platform::shell(n)
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