Bash script to capture input, run commands, and print to file

Question

I am trying to do a homework assignment and it is very confusing. I am not sure if the professor's example is in Perl or bash, since it has no header. Basically, I just need help with the meat of the problem: capturing the input and outputting it. Here is the assignment:

In the session, provide a command prompt that includes the working directory, e.g., $./logger/home/it244/it244/hw8$
Accept user’s commands, execute them, and display the output on the screen.
During the session, create a temporary file “PID.cmd” (PID is the process ID) to store the command history in the following format (index: command):

1: ls
2: ls -l
If the script is aborted by CTRL+C (signal 2), output a message “aborted by ctrl+c”.
When you quit the logging session (either by “exit” or CTRL+C),

a. Delete the temporary file

b. Print out the total number of the commands in the session and the numbers of successful/failed commands (according to the exit status).

Here is my code so far (which did not go well, I would not try to run it):

  #!/bin/sh
  trap 'exit 1' 2
  trap 'ctrl-c' 2

  echo $(pwd)
  while true
  do
    read -p command
    echo "$command:" $command >> PID.cmd
 done

Currently when I run this script I get

command read: 10: arg count

What is causing that?

======UPDATE=========

Ok I made some progress not quite working all the way it doesnt like my bashtrap or incremental index

#!/bin/sh
index=0
trap bashtrap INT
bashtrap(){
     echo "CTRL+C aborting bash script"
}
echo "starting to log"
while : 
do
    read -p "command:" inputline
    if [ $inputline="exit" ]
    then
            echo "Aborting with Exit"
            break
    else
            echo "$index: $inputline" > output
            $inputline 2>&1 | tee output
            (( index++ ))   
    fi
done

What specifically is snagging you? You don't have a lot down to work with as it seems you're only starting to scratch the surface. — Grambot
– Grambot, Commented Nov 22, 2011 at 21:56
added comment I am just looking at the slides and examples my prof has but they are scarce so I assumed that would at least allow me to input and output commands however I get the error posted above and cannot ctrl-c — BillPull
– BillPull, Commented Nov 22, 2011 at 22:00
Getting closer! I've posted a working example tested on SLES11SP1. I trust you'll go through it line by line and not just turn it in. In particular, there's a bit of code-fu in there to determine the cwd that you'll have to explain to teacher if you use it as-is. :-) +1 for effort, by the way. — T.Rob
– T.Rob, Commented Nov 23, 2011 at 3:27

hornetbzz · Accepted Answer · 2011-11-23 01:25:45Z

This can be achieved in bash or perl or others.

Some hints to get you started in bash :

question 1 : command prompt /logger/home/it244/it244/hw8
1) make sure of the prompt format in the user .bashrc setup file: see PS1 data for debian-like distros.
2) cd into that directory within you bash script.

question 2 : run the user command
1) get the user input

read -p "command : " input_cmd

2) run the user command to STDOUT

bash -c "$input_cmd"

3) Track the user input command exit code

 echo $?

Should exit with "0" if everything worked fine (you can also find exit codes in the command man pages).

3) Track the command PID if the exit code is Ok

 echo $$ >> /tmp/pid_Ok

But take care the question is to keep the user command input, not the PID itself as shown here.

4) trap on exit
see man trap as you misunderstood the use of this : you may create a function called on the catched exit or CTRL/C signals.

5) increment the index in your while loop (on the exit code condition)

index=0
while ...
   do
   ...
   ((index++)) 
   done

I guess you have enough to start your home work.

T.Rob · Accepted Answer · 2011-11-23 03:23:52Z

Since the example posted used sh, I'll use that in my reply. You need to break down each requirement into its specific lines of supporting code. For example, in order to "provide a command prompt that includes the working directory" you need to actually print the current working directory as the prompt string for the read command, not by setting the $PS variable. This leads to a read command that looks like:

read -p "`pwd -P`\$ " _command

(I use leading underscores for private variables - just a matter of style.)

Similarly, the requirement to do several things on either a trap or a normal exit suggests a function should be created which could then either be called by the trap or to exit the loop based on user input. If you wanted to pretty-print the exit message, you might also wrap it in echo commands and it might look like this:

_cleanup() {
   rm -f $_LOG
   echo
   echo $0 ended with $_success successful commands and $_fail unsuccessful commands.
   echo
   exit 0
}

So after analyzing each of the requirements, you'd need a few counters and a little bit of glue code such as a while loop to wrap them in. The result might look like this:

#/usr/bin/sh

# Define a function to call on exit
_cleanup() {
   # Remove the log file as per specification #5a
   rm -f $_LOG

   # Display success/fail counts as per specification #5b
   echo
   echo $0 ended with $_success successful commands and $_fail unsuccessful commands.
   echo
   exit 0
}

# Where are we?  Get absolute path of $0
_abs_path=$( cd -P -- "$(dirname -- "$(command -v -- "$0")")" && pwd -P )

# Set the log file name based on the path & PID
# Keep this constant so the log file doesn't wander
# around with the user if they enter a cd command
_LOG=${_abs_path}/$$.cmd

# Print ctrl+c msg per specification #4
# Then run the cleanup function
trap "echo aborted by ctrl+c;_cleanup" 2

# Initialize counters
_line=0
_fail=0
_success=0

while true
do
   # Count lines to support required logging format per specification #3
   ((_line++))
   # Set prompt per specification #1 and read command
   read -p "`pwd -P`\$ " _command

   # Echo command to log file as per specification #3
   echo "$_line: $_command" >>$_LOG

   # Arrange to exit on user input with value 'exit' as per specification #5
   if [[ "$_command" == "exit" ]]
   then
      _cleanup
   fi

   # Execute whatever command was entered as per specification #2
   eval $_command

   # Capture the success/fail counts to support specification #5b
   _status=$?
   if [ $_status -eq 0 ]
   then
     ((_success++))
   else
     ((_fail++))
   fi
done

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