| 13. | Write a script that takes a colon-separated list of items and outputs the items, one per line, to standard output (without the colons). |
| 14. | Generalize the script written in exercise 13 so that the character separating the list items is given as an argument to the function. If this argument is absent, the separator should default to a colon. |
| 15. | Write a function named funload that takes as its single argument the name of a file containing other functions. The purpose of funload is to make all functions in the named file available in the current shell; that is, funload loads the functions from the named file. To locate the file, funload searches the colon-separated list of directories given by the environment variable FUNPATH. Assume that the format of FUNPATH is the same as PATH and that searching FUNPATH is similar to the shell's search of the PATH variable. |
| 16. | Rewrite bundle (page 910) so that the script it creates takes an optional list of filenames as arguments. If one or more filenames are given on the command line, only those files should be re-created; otherwise, all files in the shell archive should be re-created. For example, suppose that all files with the filename extension .c are bundled into an archive named srcshell, and you want to unbundle just the files test1.c and test2.c. The following command will unbundle just these two files: $ bash srcshell test1.c test2.c
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| 17. | What kind of links will the lnks script (page 886) not find? Why? |
| 18. | In principle, recursion is never necessary. It can always be replaced by an iterative construct, such as while or until. Rewrite makepath (page 950) as a nonrecursive function. Which version do you prefer? Why? |
| 19. | Lists are commonly stored in environment variables by putting a colon (:) between each of the list elements. (The value of the PATH variable is a good example.) You can add an element to such a list by catenating the new element to the front of the list, as in PATH=/opt/bin:$PATH
If the element you add is already in the list, you now have two copies of it in the list. Write a shell function named addenv that takes two arguments: (1) the name of a shell variable and (2) a string to prepend to the list that is the value of the shell variable only if that string is not already an element of the list. For example, the call addenv PATH /opt/bin
would add /opt/bin to PATH only if that pathname is not already in PATH. Be sure that your solution works even if the shell variable starts out empty. Also make sure that you check the list elements carefully. If /usr/opt/bin is in PATH but /opt/bin is not, the example just given should still add /opt/bin to PATH. (Hint: You may find this exercise easier to complete if you first write a function locate_field that tells you whether a string is an element in the value of a variable.) |
| 20. | Write a function that takes a directory name as an argument and writes to standard output the maximum of the lengths of all filenames in that directory. If the function's argument is not a directory name, write an error message to standard output and exit with nonzero status. |
| 21. | Modify the function you wrote for exercise 20 to descend all subdirectories of the named directory recursively and to find the maximum length of any filename in that hierarchy. |
| 22. | Write a function that lists the number of ordinary files, directories, block special files, character special files, FIFOs, and symbolic links in the working directory. Do this in two different ways: Use the first letter of the output of ls l to determine a file's type. Use the file type condition tests of the [[ expression ]] syntax to determine a file's type.
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| 23. | Modify the quiz program (page 956) so that the choices for a question are randomly arranged. |
