添加PATH环境变量：
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[root@localhost u-boot-sh4]#export PATH=/opt/STM/STLinux-2.3/devkit/sh4/bin:$PATH
查看PATH环境变量：
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[root@localhost u-boot-sh4]#echo $PATH
/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin
原文：http://www.cnblogs.com/lovecc/p/4421631.html