Assignment 4.1 Essay

Assignment 4.1:
Page 249 exercise 1, 3, 4, and 6
1. What does the shell ordinarily do while a command is executing? What should you do if you do not want for a command to finish before running another command?
Answer: While the command is executing, the shell waits for the process to finish. Or sleeps
2. Using sort as a filter, rewrite the following sequence of commands:
$ sort list > temp, $ lpr temp, $ rm temp
Answer: $ cat list | sort | lpr
3. What is a PID number? Why are these numbers useful when you run processes in the background? Which utility displays the PID numbers of the commands you are running?
Answer: PID process identification numbers. Each of these numbers identifies the command running in the background.
6. Give a command to:
A. redirect the standard output from a sort command into a file named phone_list. Assume that the input file is named numbers.
Answer: $ sort numbers > phone_list
B. Translate all occurrences of the characters [ and { to the character (, and all occurrences of the characters ] and } to the character ) in the file permdemos.c. (Hint: Refer to the tr man page.)
Answer: $ cat permdemos.c | tr '[{}]' '(())' or $ tr '[{}]' '(())' < permdemos.c
C. Create a file named book that contains the contents of two other files: part1 and part2.
Answer: $ cat part[12] > book
11. In experimenting with shell variable, Alex accidentally deletes his PATH variable. He decides that he does not need the path variable. Discuss some of the problems he may soon encounter and explain the reasons for these problems. How could he easily return PATH to its original value?
Answer: and sends the standard output to aaa. The ls command fails and sends an error message to standard error (you see it on screen). Even though the ls command failed, the empty file named exists. Because the ls command failed, it did not create the file;