Environment Variables

echo $SHELL  # current shell
echo $PWD   # current directory
echo $USER  # current user name
echo $HOME  # home directory of current user
echo $PATH  # system path

Permenant Setting

~/.bashrc or ~/.bash_profile:

export X="xxx"
export PATH="xxx:$PATH"

Run:

. ~/.bashrc

or

source ~/.bashrc

Temporary Disable

unset XXX

GNU comformance to POSIX

POSIXLY_CORRECT

GNU utility conformance to POSIX Std.

export POSIXLY_CORRECT=true

Different POSIX Std version

# POSIX 1003.1-2001
export _POSIX2_VERSION=200112

# POSIX 1003.2-1992
export _POSIX2_VERSION=199209