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Operating Systems Solaris export vs env vs set commands Post 302531838 by bartus11 on Saturday 18th of June 2011 07:34:32 AM
Old 06-18-2011
Quote:
Originally Posted by presul
What does it mean to make a value of variable known to a sub-shell ?
Code:
[root@linux ~]# x=5                       <= here variable is set without export command
[root@linux ~]# echo $x
5
[root@linux ~]# bash                      <= subshell creation
[root@linux ~]# echo $x                   <= subshell doesnt know $x variable value

[root@linux ~]# exit                      <= exit from subshell
exit
[root@linux ~]# echo $x                   <= parent shell still knows $x variable
5
[root@linux ~]# export x=5                <= specify $x variable value using export command
[root@linux ~]# echo $x                   <= parent shell doesn't see any difference from the first declaration
5
[root@linux ~]# bash                      <= create subshell again
[root@linux ~]# echo $x                   <= now the subshell knows $x variable value
5
[root@linux ~]#

 
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env(1)							      General Commands Manual							    env(1)

NAME
env, printenv - Displays or sets the current environment, or displays the values of environment variables SYNOPSIS
Current Syntax env [-i] [name=value...] [command] [args...] printenv [name] Obsolescent Syntax env [-] [name=value...] [command] [args...] STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: env: XCU5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. OPTIONS
Invokes utility with exactly the environment specified by the arguments; the inherited environment is ignored completely. Changes are in effect only while the specified command is running. Dash is equivalent to -i option. OPERANDS
Changes in the form name=value are added to the current environment before the command is run. [Tru64 UNIX] Name of an environment vari- able to be printed. Name of a command to be invoked with the modified environment. Arguments to be passed to command when it is executed. DESCRIPTION
The env command lets you get and change your current environment, and then run the specified command with the changed environment. If the -i option is used, the current environment is ignored and the command runs with only the changed environment. Changes are only in effect while the specified command is running. If command is not specified, env displays your current environment, one name=value pair per line. [Tru64 UNIX] The printenv command displays the values of the variables in the environment. If name is specified, only its value is printed. If name is not the name of a currently set environment variable, only a blank line is printed, no error is reported. If name is not specified, printenv displays the current environment, one name=value per line. EXIT STATUS
If command is invoked, the exit status of env is the exit status of command; otherwise, the env utility exits with one of the following values: The env utility completed successfully. An error occurred in the env utility. The command specified by command was found but could not be invoked. The command specified by command could not be found. EXAMPLES
To add a shell variable to the environment for the duration of one command (sh only), enter: TZ=MST7MDT date env TZ=MST7MDT date Each of these commands displays the current date and time in Mountain Standard Time. The two commands shown are equivalent. When date is finished, the previous value of TZ takes effect again. To replace the environment with another one, enter: env -i PATH=$PATH IDIR=/u/jim/include LIBDIR=/u/jim/lib make This runs make in an environment that consists only of these definitions for PATH, IDIR, and LIBDIR. You must redefine PATH so that the shell can find the make command. When make is finished, the previous environment takes effect again. To find the current setting of the TERM environment variable, enter: printenv TERM The command returns the value for the TERM environment variable. ENVIRONMENT VARIABLES
The following environment variables affect the execution of env: Provides a default value for the internationalization variables that are unset or null. If LANG is unset or null, the corresponding value from the default locale is used. If any of the internationalization vari- ables contain an invalid setting, the utility behaves as if none of the variables had been defined. If set to a non-empty string value, overrides the values of all the other internationalization variables. Determines the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multibyte characters in arguments). Determines the locale for the for- mat and contents of diagnostic messages written to standard error. Determines the location of message catalogues for the processing of LC_MESSAGES. SEE ALSO
Commands: csh(1), ksh(1), Bourne shell sh(1b), POSIX shell sh(1p) Functions: exec(2) Standards: standards(5) env(1)

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