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Full Discussion: Read command acting erratically
Top Forums Shell Programming and Scripting Read command acting erratically Post 302910299 by Corona688 on Wednesday 23rd of July 2014 12:46:31 PM
Old 07-23-2014
Consider what happens when you do a |

Code:
echo a b c | some program

If "some program" were cat, would it change any memory or variables in your current shell? Of course not, it doesn't have access to them -- it's a separate process. All commands run after a pipe, including shell built-ins, have to run in a new process.

So read is run in a brand-new, independent shell, which happily sets the variable x in that shell -- then immediately dies, leaving the original shell unchanged.

Try this:

Code:
echo A | ( read X ; echo $X )

Here it will work because the read and the echo are grouped in the same shell.

ksh does pipes in the opposite order so "echo | read" will actually work -- but this isn't something you can count on unless you know you have KSH.
This User Gave Thanks to Corona688 For This Post:
Michael Stora
 

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LEARN ABOUT CENTOS

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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