college/Summer-2024/CS-3424/Midterm-Notes.org

• Systems Programming Midterm Topics
• Example Questions

Systems Programming Midterm Topics

1. Linux environment / shell commands

   • Common commands
   • Chmod/permissions
   • Wildcards
   • Input/output redirection
   • Shell parsing steps

   • Shell command resolution variables

     • Shell vs environment and their inheritance
   • Exit statuses
   • Subshells / child shells

   • Arithmetic (operators: expansion vs evaluation)

     • Floating arithmetic in bash: how?
2. Bash Scripting
3. find~/~grep
4. Regular expressions (BRE vs ERE)
5. sed

NOTE: No AWK material will be covered on the exam

Example Questions

1. Answer True or False for the following statements:

   • [TRUE] The extended regular expression {0,1} is equivalent to the ? quantifier?
   • [FALSE] An exit status of 0 is used to indicate success.
   • [FALSE] Given the string "abc123" the regex /[a-z]{1,3}/ will produce a match of "a".

   • [FALSE] The following loop will never execute:

     while [ 0 ]; do let i++; echo $i; done

   • [TRUE] The following loop will never execute:

     while (( 0 )); do let i++; echo $i; done

   • [TRUE] sed will emit the contents of the pattern space, including a trailing newline character, by default at the end of each input cycle.

   • [FALSE] The following bash filename pattern will match all text files in the user's current directory:

     ls -la .*\.txt

   • [TRUE] The source built-in executes the contents of a specified file within the current script (i.e. no subshell is utilized).
   • [FALSE] grep uses extended regular expressions by default
2. Enter the octal number corresponding to the following Linux file permissions: rwxr-x--- Answer: 0750

3. Write out the erroneous line numbers from the following script (hint there are six):

   data="./data"
   org_data=/usr/local/courses/ssilvestro/cs3424/Spring21/assign1/
   
   if [[ $# -eq 1 ]]; then
       data = $1
   else if [[ $# -eq 2 ]]; then
       data = $1
       orig_data = $2
   fi
   
   if [[! -d $data]]; then
       echo "ERROR: data directory '$data' does not exist"
       exit 1
   fi
   if [[ not -d $orig_data ]]; then
       echo "ERROR: original data directory '$data' does not exist"
       exit 1
   fi
   echo "rm -rf \"$data\"..."
   rm -rf "$data"
   
   echo "cp -r \"$org_data\" \"$data\"..."
   cp -r "$orig_data" "$data"

   Answer: 4,5,6,7,9,13