Advanced Bash−Scripting Guide. An in−depth exploration of by Cooper M.

By Cooper M.

This instructional assumes no earlier wisdom of scripting or programming, yet progresses swiftly towards an intermediate/advanced point of guideline ...all the whereas sneaking in little snippets of UNIX knowledge and lore. It serves as a textbook, a handbook for self-study, and a reference and resource of data on shell scripting thoughts. The routines and heavily-commented examples invite lively reader participation, lower than the idea that the one technique to fairly examine scripting is to write down scripts.

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Bash has the test command, various bracket and parenthesis operators, and the if/then construct. 1. Test Constructs • An if/then construct tests whether the exit status of a list of commands is 0 (since 0 means "success" by UNIX convention), and if so, executes one or more commands. • There exists a dedicated command called [ (left bracket special character). It is a synonym for test, and a builtin for efficiency reasons. This command considers its arguments as comparison expressions or file tests and returns an exit status corresponding to the result of the comparison (0 for true, 1 for false).

Shft a b c def 23 skidoo until [ −z "$1" ] do echo −n "$1 " shift done # Until all parameters used up... echo # Extra line feed. exit 0 The shift command also works on parameters passed to a function. See Example 34−10. Chapter 4. Introduction to Variables and Parameters 31 Chapter 5. Quoting Quoting means just that, bracketing a string in quotes. This has the effect of protecting special characters in the string from reinterpretation or expansion by the shell or shell script. sh bash$ ls −l '[Vv]*' ls: [Vv]*: No such file or directory Certain programs and utilities can still reinterpret or expand special characters in a quoted string.

Export var&=ZZZZZZZZZZZZZZ/'`" bash$ du bash: /usr/bin/du: Argument list too long (Thank you, S. C. ) If a script sets environmental variables, they need to be "exported", that is, reported to the environment local to the script. This is the function of the export command. A script can export variables only to child processes, that is, only to commands or processes which that particular script initiates. A script invoked from the command line cannot export variables back to the command line environment.

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