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Homework and Emergencies Homework & Coursework Questions New user needs help with bourne shell script Post 302939060 by Don Cragun on Sunday 22nd of March 2015 02:12:33 AM
Old 03-22-2015
Please use CODE tags when displaying sample input, output, and code.

You should look at the man page for your shell (presumably man sh for the Bourne shell). Look for the words "Background" and "background" in that man page for ways to run a process in the background and restrictions on what a background job can do. You don't seem to have anything in your script to run any processes in the background.

Also look for "Redirection" and "redirection" to see what > file does when it is used as a complete command, and what it does when it is used as part of a larger command.

And look for "Pipeline" and "pipeline". Having two processes in a pipeline that redirect standard output to the same file creates a race condition that may make it impossible to determine which process writing to that file will actually store lasting data in that file.

Then take a look at the man page for the cat utility. The command:
Code:
cat > file

doesn't necessarily create an empty file named file; it depends entirely on what cat reads from its standard input.

Is your understanding of part "a)" of your assignment that the output should include all of your files (including hidden files); or that the output should only include your hidden files?
 

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CAT(1)							    BSD General Commands Manual 						    CAT(1)

NAME
cat -- concatenate and print files SYNOPSIS
cat [-benstuv] [file ...] DESCRIPTION
The cat utility reads files sequentially, writing them to the standard output. The file operands are processed in command-line order. If file is a single dash ('-') or absent, cat reads from the standard input. If file is a UNIX domain socket, cat connects to it and then reads it until EOF. This complements the UNIX domain binding capability available in inetd(8). The options are as follows: -b Number the non-blank output lines, starting at 1. -e Display non-printing characters (see the -v option), and display a dollar sign ('$') at the end of each line. -n Number the output lines, starting at 1. -s Squeeze multiple adjacent empty lines, causing the output to be single spaced. -t Display non-printing characters (see the -v option), and display tab characters as '^I'. -u Disable output buffering. -v Display non-printing characters so they are visible. Control characters print as '^X' for control-X; the delete character (octal 0177) prints as '^?'. Non-ASCII characters (with the high bit set) are printed as 'M-' (for meta) followed by the character for the low 7 bits. EXIT STATUS
The cat utility exits 0 on success, and >0 if an error occurs. EXAMPLES
The command: cat file1 will print the contents of file1 to the standard output. The command: cat file1 file2 > file3 will sequentially print the contents of file1 and file2 to the file file3, truncating file3 if it already exists. See the manual page for your shell (i.e., sh(1)) for more information on redirection. The command: cat file1 - file2 - file3 will print the contents of file1, print data it receives from the standard input until it receives an EOF ('^D') character, print the con- tents of file2, read and output contents of the standard input again, then finally output the contents of file3. Note that if the standard input referred to a file, the second dash on the command-line would have no effect, since the entire contents of the file would have already been read and printed by cat when it encountered the first '-' operand. SEE ALSO
head(1), more(1), pr(1), sh(1), tail(1), vis(1), zcat(1), setbuf(3) Rob Pike, "UNIX Style, or cat -v Considered Harmful", USENIX Summer Conference Proceedings, 1983. STANDARDS
The cat utility is compliant with the IEEE Std 1003.2-1992 (``POSIX.2'') specification. The flags [-benstv] are extensions to the specification. HISTORY
A cat utility appeared in Version 1 AT&T UNIX. Dennis Ritchie designed and wrote the first man page. It appears to have been cat(1). BUGS
Because of the shell language mechanism used to perform output redirection, the command ``cat file1 file2 > file1'' will cause the original data in file1 to be destroyed! The cat utility does not recognize multibyte characters when the -t or -v option is in effect. BSD
March 21, 2004 BSD
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