String Operators

The curly-bracket syntax allows for the shell's string operators. String operators allow you to manipulate values of variables in various useful ways without having to write full-blown programs or resort to external UNIX utilities. You can do a lot with string-handling operators even if you haven't yet mastered the programming features we'll see in later chapters.

In particular, string operators let you do the following:

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  • Ensure that variables exist (i.e., are defined and have non-null values)
  • Set default values for variables
  • Catch errors that result from variables not being set
  • Remove portions of variables' values that match patterns