如何debug shell脚本呀？

hoverfly

一个脚本，用来终止指定的进程。可以运行有错误，我想知道如何能debug它呀？脚本如下：

#!/bin/sh
## zap -- send a kill signal to processes by name

usage()
{
        echo "usage: $Prg -[c [f|h]] pname ..."
        echo "-c ask for confirmation"
        echo "-f sends a SIGKILL signal (default is SIGTERM)"
        echo "-h sends a SIGHUP signal"
        echo
        echo "Where pname is the process name(s) you want to zap."
        exit 1;
}

askyn() # ask for confirmation before continuing
{
        $ECHO "zap $* (y/n?)[n]: $el"
        read ans < /dev/tty # read from the terminal device
        case $ans in
                Y|y) return 1;;
                        *) return 0;; # anything other than y or Y is a no.
        esac
}

process()
{
        $PS | egrep "^$LOGNAME" | \
        while read line # read the output from ps
        do
                # does the command name match?
                if [`basename \`echo $line | cut -f$cmd -d" "\`` = "$1" ];then
                        # should we confirm the kill?
                        if [ $confirm -eq 1 ]; then
                                if askyn $line; then
                                        continue # on to the next case
                                fi
                        fi
                        # zap it
                        echo "zapping: $line"
                        kill -$signal `echo $line | cut -f$pid -d" "`
                fi
        done
}

Prg=`basename $0` # $0 contains the program name
confirm=0 # default is no confirmation
singal=15 # send the software terminate signal by default

pid=2 # field 2 of the ps command contains the process id
ps -x >/dev/null 2>&1 # if this works assume BSD style ps
if [ $? -eq 0 ]; then # $? contains the error level of the last command executed
        PS="ps -aux"
        cmd=11 # field 11 contains the command
else # assume Sysyem V style ps
        PS="ps -ef"
        cmd=8 # field 8 contains the command
fi
if [ `echo "hi \c" | wc -w` -eq 2 ];then
        ECHO="echo -n"; el="" # we have the -n switch
else
        ECHO=echo; el="\c" # \c tells echo not to print newline
fi

# test to make sure we have at least one argument
[ $# -lt 1 ] && usage

# use the getopts command to parse the command line
while getopts cfh i
do
        case "$i" in
        c) confirm=1;;
        f) [ $signal -ne 15 ] && echo "the -f and -h switches are mutually exclusive." && usage
                signal=9;;
        h) [ $signal -ne 15 ] && echo "the -f and -h switches are mutually exclusive." && usage
                signal=1;;
        '?') usage;;
        esac
done
shift `expr $OPTION - 1` # shift command line switches out of the way
[ -z "$1" ] && echo "No process was specified." && usage
while [ ! -z "$1" ] # for each process name specified
do
        process $1
        shift # shift the remaining arguments left
done
exit 0

寂寞烈火

#!/bin/sh -xv