How to extract the first two characters of a string in shell scripting?

Question

For example, given:

USCAGoleta9311734.5021-120.1287855805

I want to extract just:

US

Answer 1

If you want to use shell scripting and not rely on non-posix extensions (such as so-called bashisms), you can use techniques that do not require forking external tools such as grep, sed, cut, awk, etc., which then make your script less efficient. Maybe efficiency and posix portability is not important in your use case. But in case it is (or just as a good habit), you can use the following parameter expansion option method to extract the first two characters of a shell variable:

$ sh -c 'var=abcde; echo "${var%${var#??}}"'
ab

This uses "smallest prefix" parameter expansion to remove the first two characters (this is the ${var#??} part), then "smallest suffix" parameter expansion (the ${var% part) to remove that all-but-the-first-two-characters string from the original value.

This method was previously described in this answer to the "Shell = Check if variable begins with #" question. That answer also describes a couple similar parameter expansion methods that can be used in a slightly different context that the one that applies to the original question here.