具体如何修改linux下/etc/profile的环境变量

最近学linux发现视频里要修改的环境变量和我电脑实际的很不一样，新手的我表示不会了。 安装好了arm-linux-gcc交叉编译器但是不会配置环境变量。求大神帮我改一下。以下是电脑中的代码：
# /etc/profile: system-wide .profile file for the Bourne shell (sh(1))
# and Bourne compatible shells (bash(1), ksh(1), ash(1), ...).

if [ "$PS1" ]; then
if [ "$BASH" ] && [ "$BASH" != "/bin/sh" ]; then
# The file bash.bashrc already sets the default PS1.
# PS1='\h:\w\$ '
if [ -f /etc/bash.bashrc ]; then
. /etc/bash.bashrc
fi
else
if [ "`id -u`" -eq 0 ]; then
PS1='# '
else
PS1='$ '
fi
fi
fi

# The default umask is now handled by pam_umask.
# See pam_umask(8) and /etc/login.defs.

if [ -d /etc/profile.d ]; then
for i in /etc/profile.d/*.sh; do
if [ -r $i ]; then
. $i
fi
done
unset i
fi

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