Shell中对选项和参数的处理方法

# A small example program for using the new getopt(1) program.
# This program will only work with bash(1)
# An similar program using the tcsh(1) script. language can be found
# as parse.tcsh

# Example input and output (from the bash prompt):
# ./parse.bash -a par1 'another arg' --c-long 'wow!*\?' -cmore -b " very long "
# Option a
# Option c, no argument
# Option c, argument more'
# Option b, argument very long '
# Remaining arguments:
# --> par1'
# --> another arg'
# --> wow!*\?'

# Note that we use "$@"' to let each command-line parameter expand to a
# separate word. The quotes around $@' are essential!
# We need TEMP as the eval set --' would nuke the return value of getopt.

#-o表示短选项，两个冒号表示该选项有一个可选参数，可选参数必须紧贴选项
#如-carg 而不能是-c arg
#--long表示长选项
#"$@"在上面解释过
# -n:出错时的信息
# -- ：举一个例子比较好理解：
#我们要创建一个名字为 "-f"的目录你会怎么办？
# mkdir -f #不成功，因为-f会被mkdir当作选项来解析，这时就可以使用
# mkdir -- -f 这样-f就不会被作为选项。

TEMP=getopt -o ab:c:: --long a-long,b-long:,c-long:: \
     -n 'example.bash' -- "$@"

if [ $? != 0 ] ; then echo "Terminating..." >&2 ; exit 1 ; fi

# Note the quotes around $TEMP': they are essential!
#set 会重新排列参数的顺序，也就是改变$1,$2...$n的值，这些值在getopt中重新排列过了
eval set -- "$TEMP"

while true ; do
        case "$1" in
                -a|--a-long) echo "Option a" ; shift ;;
                -b|--b-long) echo "Option b, argument $2'" ; shift 2 ;;
                -c|--c-long)
                        # c has an optional argument. As we are in quoted mode,
                        # an empty parameter will be generated if its optional
                        # argument is not found.
                        case "$2" in
                                "") echo "Option c, no argument"; shift 2 ;;
                                *)  echo "Option c, argument $2'" ; shift 2 ;;
                        esac ;;
                --) shift ; break ;;
                *) echo "Internal error!" ; exit 1 ;;
        esac
done
echo "Remaining arguments:"
for arg do
   echo '--> '"$arg'" ;
done