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Associated Information

my_prog arg1 arg2 arg3 is equivalent to $0 $1 $2 $3

• $0 - gives program name, i.e. my_prog
• $* - gives all arguements i.e. $i , $2 and $3
• $# - gives number of arguements, i.e. 3
• $? - gives return code
• $$ - gives pid, useful for assigning unique names, e.g. > /tmp/file.$$

These can be used to create a usage statement (which is always good practice), e.g.

Parameter Subsitution

${variable:-string}

will show variable if set otherwise string

${variable:=string}

if variable is not set, use string and set variable to the value of string for