As usual, keep a log in the file lab5.txt of what you do in the lab so that you can reproduce the results later. This should not merely be a transcript of what you typed: it should be more like a true lab notebook, in which you briefly note down what you did and what happened.
You're helping to maintain an old stable version of coreutils, but that version has a bug in its implementation of the ls program. (Actually, it has two bad bugs, but for now we'll just look at the first one.)
The bug is that ls -t mishandles files whose time stamps are very far in the past. It seems to act as if they are in the future. For example:
$ touch -d '1918-11-11 11:00 GMT' wwi-armistice $ touch now $ sleep 1 $ touch now1 $ ls -lt wwi-armistice now now1 -rw-r--r-- 1 eggert eggert 0 Nov 11 1918 wwi-armistice -rw-r--r-- 1 eggert eggert 0 Feb 5 15:57 now1 -rw-r--r-- 1 eggert eggert 0 Feb 5 15:57 now
Build this old version of coreutils as-is, and then again with this renaming patch. What problems did you have when building it as-is, and why did the renaming patch fix them?
Reproduce the problem. Use a debugger to figure out what went wrong and to fix the corresponding source file.
Construct a new patch file lab5.diff containing your fixes, in the form of a ChangeLog entry followed by a diff -u patch.
Write a program binsortu that takes a single argument N (where N is a positive decimal integer), reads N-byte records from standard input, sorts them in lexicographic order, removes duplicates, and outputs the result to standard output. If standard input ends in a partial record that contains fewer than N bytes, binsortu should treat it as if it were padded with trailing null ('\0') bytes, which should cause this padded record to appear relatively early in the output.
Use lexicographic byte comparison to compare each record, in the style of the memcmp function, and remove duplicates; for example, the following input:
DACC ABDB CDDB BCCB BCCB CDDB DACC BDCC
should generate the following output:
ABDB BCCB BDCC CDDB DACC
assuming the record size is five bytes (four letters plus a newline byte).
Use <stdio.h> functions to do I/O. Use malloc, realloc and free to allocate enough storage to hold all the input, and use qsort to sort the data. Do not assume that the input file is not growing: some other process may be appending to it while you're reading, and your program should continue to read until it reaches end of file. For example, your program should work on the file /proc/self/maps, a "file" that is constantly mutating: it always appears to be of size 0 when you ls it, but it always contains nonempty contents if you read it. You should make sure your program works on empty files, as well as on files that are relatively large, such as /usr/local/cs/jdk1.7.0/jre/lib/rt.jar on SEASnet.
Accept any positive decimal integer string N that strtoul would. If the program encounters an error of any kind (including input, output or memory allocation failures, missing or extra arguments, an N that is not a positive integer or is too large to be represented), it should report the error to stderr and exit with status 1; otherwise, the program should succeed and exit with status 0. The program need not report stderr output errors.
For example, the command:
printf '\x00CA\x00D\x00\x00B' | ./binsortu 2 | od -c
should output:
0000000 \0 B \0 C A \0 D \0 0000010
Also, assuming there are no control characters other than tabs and newlines in your source file, the command:
export LC_ALL='C'
maxsize=$(expand <binsortu.c | awk '
BEGIN { maxlen = 0 }
{ if (maxlen < length) maxlen = length }
END { print maxlen + 1 }
')
expand <binsortu.c |
awk -v maxsize=$maxsize '{printf "%-*s\n", maxsize - 1, $0}' |
./binsortu $maxsize |
sed 's/[[:space:]]*$//' > test1.txt
sed 's/[[:space:]]*$//' binsortu.c | sort -u >test2.txt
cmp test1.txt test2.txt
should output nothing.
Submit the following files.
All files should be ASCII text files, with no carriage returns, and with no more than 200 columns per line. The C source file should contain no more than 132 columns per line. The shell commands
expand lab5.txt lab5.diff | awk '/\r/ || 200 < length' expand binsortu.c | awk '/\r/ || 132 < length'
should output nothing.