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Shell Programming and Scripting

Exit status

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# 8  
Old 09-08-2008
Quote:
Originally Posted by MartyIX
> Do you have to do it without external commands?

I'm not sure what you exactly mean. I may use whatever command except test - I got the assignment this way.

If you can use external commands, i.e., those that are not built into the shell, like awk, sed, expr, etc., it becomes an exercise in parsing arguments, since external commands can do all the testing for you.
Quote:
> I look forward to seeing it.
I don't think you'll be pleased with great source code :-)

It's not too bad, though you should look at using case statements instead of external commands whenever possible; it will speed up your script. For example:

Code:
case $# in
   0) usage; exit 1;;
   1) ## if 1 arg, check for null string
      case $1 in
         "") exit 1 ;; ## empty string
         *) exit 0 ;;
      esac
   2) two_args "$@" ;; ## two_args() checks unary operators
   3) three_args "$@" ;; ## three_args() checks binary operators
   4) four_args "%@" ;;
   * ) parse_compound_tests ;; ## etc...
esac

##

# 9  
Old 09-09-2008
Quote:
If you can use external commands, i.e., those that are not built into the shell, like awk, sed, expr, etc., it becomes an exercise in parsing arguments, since external commands can do all the testing for you.
Well yes, in fact without external commands I would be at a loss - it would be pretty much work

Quote:
>I don't think you'll be pleased with great source code :-)
It's not too bad
... and I thought right :-)))

Sure you're right -> one example of bad code for all:

Code:
      if expr2 $num_stack ">" 2; then
      
        echo "Error: Stack overflow";
        exit 1;
      
      elif expr2 $num_stack "=" 2; then      
        return 0;      
      else       
        return 1                    
      fi

I'll try to adjust the code..
# 10  
Old 09-09-2008
New commands: -nt, -ot, -ef

I've adjusted the code and it seems to speed up at least twice:

Code:
#!/bin/sh   


  # File: test.sh
  # Author: Martin Vseticka, 2008  
  
  verbose=0;

  debug_info() {
  
    case $verbose in
      [0]) return 0;;
      [1]) echo "$@" >&2
    esac         
  }
  
  expr2() { # expr without output
   
    result=$( expr "$@" )
    return $( expr $result "=" 0 )  
  }
  
  usage() {
  
    echo "Usage: "; # TODO   
  }


  process() {
    
    num_stack=0;
    op_stack=0;
    number1=0;
    number2=0;
    op="";    
    opened_with_logical_switch=$1;
    deepness=$2    
    shift 2;
    
    num_stack_in() {  # number stack
      
      num_stack=$(( $num_stack + 1 ));

      debug_info "Deepness: $deepness; Num_stack: $num_stack; Value: $1"      

      eval "number${num_stack}=$1"            
      
      case $num_stack in
        [0]|[1]) return 1;;
            [2]) return 0;;
              *) echo "Error: Stack overflow";
                 exit 1;;
      esac           
 
    }
    
    op_stack_in() {  # operation stack
    
      op_stack=$(( $op_stack + 1 ));
      eval "op${op_stack}=\"$1\""      
                
    }

    op_stack_out() {
    
      eval "op=\$op${op_stack};"
      op_stack=$(( $op_stack - 1 ));
    }

    do_op() {
    
      op_stack_out;
      
      case "$op" in        
        "="|">"|"<"|"!=") num_stack=0;
                          num_stack_in $(expr $number1 "$op" $number2);;        
 
               "-a"|"-o") num_stack=0;
                          case "$number1 $number2" in
                            '1 1') num_stack_in 1;;
                                *) num_stack_in 0;;
                          esac;;
                   '-ef') num_stack=0; 
                          do_op_equal=$(ls -i "$number1" "$number2" | while read inode_num file; do
                                               echo $inode_num
                                        done | tr "\n" " " | awk '{ if ($1 == $2){ print "1"; }else{ print "0"; } }' );                                                                               
                          
                          if expr2 "$do_op_equal" "=" "1" &&
                             expr2 "$(stat -c %D "$number1")" "=" "$(stat -c %D "$number2")" && 
                             expr2 "$(stat -c %D "$number1")" "=" "$(stat -c %D "$number2")"; then
                            num_stack_in 1;
                          else
                            num_stack_in 0;      
                          fi;;    
             '-nt'|'-ot') case "$op" in
                            '-nt') do_op_res=$(find "$number1" -newer "$number2" -print);;
                            '-ot') do_op_res=$(find "$number2" -newer "$number1" -print);;   
                          esac   
                          # any do_op_res ~ true; otherwise false
                          case "dd${do_op_res}dd" in
                            'dddd') switch=0;;
                                 *) switch=1;;
                          esac 
                          num_stack=0;
                          num_stack_in $switch;;
                          
                       *) echo "Unknown operation: "'`'"$op\""; exit 1;;
      esac
    
    }

    
    while true; do
           
      case $# in      
        [0]) break;;   # stop the main loop
      esac
      
      switch="$1"
      debug_info 'Deepness: '"$deepness"'; Switch: `'"$switch\""
      shift      
      
      case "$switch" in
         
          ')')  echo "$number1 $#";
                return 0;;
         
          '(')  partial_result=$(process 0 $(( $deepness + 1 )) "$@");
                switch=$(echo "$partial_result" | cut -d" " -f 1);
                remaining_switches=$(echo "$partial_result" | cut -d" " -f 2);                
                shift $(($# - $remaining_switches));; # shift after ")"
         
          # test if $1 is empty
          "-z") case "dd${1}dd" in
                  'dddd') switch=0;;
                       *) switch=1;;
                esac
                shift;;
          
          # test if $1 is non-zero length string
          "-n") case "dd${1}dd" in
                  'dddd') switch=0;;
                       *) switch=1;;
                esac                        
                shift;;                                  
      esac
      
      case "$switch" in      
                 "-a"|"-o") case $opened_with_logical_switch in
                              [1])  # $# + 1 because we want to process -a or -o again. 
                                    # (in this function the switch -a / -o are shifted)
                                    echo "$number1 "$(($# + 1)); 
                                    return 0;;
                            esac 

                            op_stack_in "$switch";

                            partial_result=$(process 1 $(( $deepness + 1 )) "$@");
                            
                            if echo "$partial_result" | grep -q '^[10]\{1\}$'; then
                              switch=$partial_result;
                              remaining_switches=0;
                            else                            
                              switch=$(echo "$partial_result" | cut -d" " -f 1);
                              remaining_switches=$(echo "$partial_result" | cut -d" " -f 2);
                            fi
                            
                            if num_stack_in $switch; then
                              do_op # with "$number1" "$number2"
                            fi
                            shift $(( $# - $remaining_switches ));;                            
                    [0-9]*) if num_stack_in "$switch"; then
                              do_op # with "$number1" "$number2"
                            fi;;
                       "=") op_stack_in "=";;
                      "!=") op_stack_in "!=";;
                       ')') op_stack_in ')';;
                       '(') op_stack_in '(';;
                     '-gt') op_stack_in '>';;
                     '-lt') op_stack_in '<';;
         '-ef'|'-ot'|'-nt') op_stack_in "$switch";;
                         *) if num_stack_in "$switch"; then
                              do_op # with "$number1" "$number2"
                            fi;;                              
                         #*) echo 'Switch `'"$switch\" - not known"; exit 2;;
      esac      
    
    done;    
    
    case "$num_stack $number1" in
     '1 1') echo 1        
            return 0;;
         *) echo 0
            return 1;;
    esac    
  
  }
  
  
  # MAIN SCRIPT STARTS HERE
  # =========================   

  # for debugging purposes; TODO - delete after finishing
  if [ "$1" == "-x" ]; then
    set -x;
    shift 1
  fi
 
  # for debugging purposes;
  if [ "$1" == "-v" ]; then
    verbose=1
    shift 1
  fi  
  
  case "$#" in
  
    0) usage;;
    *) process 0 "1" "$@"               # verbose version
       # process "1" "$@" >/dev/null    # silent version
       exit $?   
  esac

Last edited by MartyIX; 09-09-2008 at 06:59 AM..
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