SubstringsOften times a programmer needs to be able to get a substring from a variable at a given position. In unix you can use the exprcommand to do this with the substr parameter. Let's say that we have the text string "5283username$$2384/" and we want to get the text "username". To do this we need to read from position 5 for a length of 8. The parameters for substr are the input string, the s..