第88页 | Learning the Bash Shell | 阅读 ‧ 电子书库

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:

 

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