Well, this goes now into bash programming: The part between the lines "cat << EOF" and "EOF" is a so called "here doc" that writes the actual pig script. Everything starting with $ is a variable ($0,$1,... are predefined in bash with $0 containing the script/program name, $1 the first actual parameter, $2 the second and so on; $@ gives back all provided parameters joined with a space ' ' by default). Note: Setting variables (e.g. FUN, TAB) is done without $, referencing with $ So you can add any logic before "cat << EOF" to set variables leveraging your input parameters and reference them in the "here doc" to get the pig script you want. For more see e.g. http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html and http://www.tldp.org/LDP/abs/html/index.html (and at many other locations).
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