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Full Discussion: difference between source, exec and ./script
Top Forums UNIX for Dummies Questions & Answers difference between source, exec and ./script Post 2037 by mib on Sunday 15th of April 2001 09:24:44 AM
Old 04-15-2001
./script creates a new shell and executes each command in the script within the new shell. When the end of the script file is encountered, the new shell exits. Any changes in the new shell caused by the script are lost when the shell exits.

For example, if the file
/home/user/sample/script/test contains...

cd /usr/games
pwd
echo hi

Then the command sequence would yield the following output:

prompt>cd /home/user/sample/script
prompt>pwd
/home/user/sample/script
prompt>chmod +x test
prompt>./test
/usr/games
hi
prompt>pwd
/home/user/sample/script

source Execution
source execute a shell script within the context of the current shell. Since execution takes place within the context of the current shell, any changes in the shell are retained following the completion of the shell.
Example:

prompt>cd /home/user/sample/script
prompt>pwd
/home/user/sample/script
prompt>source test
/usr/games
hi
prompt>pwd
/usr/games


Execing a <command> (ie. shell script or executable) means give exec <command> on the shell prompt.

The exec command will execute a command in place of the current shell, that is, it terminates the current shell and starts a new process in its place.

exec was often used to execute the last command of a shell script. This would kill the shell slightly earlier; otherwise, the shell would wait until the last command was finished. This practice saves a process and some memory.

try exec ls. you will be logged out from your login shell.

exec also manipulates file descriptors in the Bourne shell.
$exec >>logoutput
after issuing this command you will not see output of any command in your console. all output goes into logoutput file.

use exec >/dev/console to return.

$exec 2>errs.out
means that from then on, stderr goes into errs.out file


hope this will help you

[Edited by mib on 04-15-2001 at 12:14 PM]
These 2 Users Gave Thanks to mib For This Post:
Kibou vinay4889
 

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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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