1、在命令行上写分支语句
read -e -p "f:" f; if [ -z "$f" ]; then echo "f is null"; else echo "f=$f"; fi
2、在命令行写循环预计
o='abc def'; for i in $o; do echo "i=$i"; done
o在文件o.txt : source o.txt; for i in $o; do echo "i=$i"; done
