while writing your own Bash shell command
 

Hi;
I have to write a couple of user defined Bash shell commands but I do not know how I will make these commands have some options(like -o,-l etc.) or have some input or output files as arguments.Thanks..

Are you writing them as shell scripts? Or functions? In either case, all arguments are available in $*, you just need to parse them. Or, if you're concerned with position, you could use $1..$n for "n" arguments.

I 'm supposed to write them as shell scripts but from the tutorials I have read so far ,I could not learn how a command recognizes a given valid(or gives an error if it is unvalid) option or uses a given file as an argument.:(

Checked your tuts for "getopts"?

Check out the Advanced bash scripting guide:

http://www.tldp.org/LDP/abs/html/