Question

My question is: What is v1,v2,v3,v4 and v5 in the below function?
They look like input parameters but I am not really sure what they are for. Can anyone explain it in a bit detail of what they do?

#!/bin/sh
compile()
{
v1="$1*z*"
v2=${2:-"$1*"}
v3=${3:-"$1*/"}
v4=${4:-"."}
v5=${5:-"."}

some other command and cd in here 

}
compile libpng
compile icu "" "" source build
.
.
.

Answer 1

$1 etc. are the arguments to the function.

And, from the bash(1) man page, EXPANSION section, Parameter Expansion subsection:

   ${parameter:-word}
          Use  Default  Values.  If parameter is unset or null, the expan‐
          sion of word is substituted.  Otherwise, the value of  parameter
          is substituted.