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boygenuis

03-02-2014 02:11 PM

Help With Homework Assignment

I'm having some issue with a homework assignment on shell scripting. The instructor gave me this pseudo code:

Code:

BEGIN

    set FINDALL to false

    IF $1 equals -a THEN

        set FINDALL to TRUE

        dispose of $1

    END-IF

    FOR each Positional Parameter ($file) DO

        IF $file is a pathname THEN

            IF if $file is executable and not a directory THEN

                echo $file

            ELSE

                echo $file  is NOT Found

            END-IF

        ELSE

            set FOUND to false

            # Don't forget to handle the special cases of PATH

            FOR  P in PATH (: separated list) DO

                IF $P/$file is executable and not a directory THEN

                    set FOUND to true

                    echo $P/$file

                    IF FINDALL is FALSE THEN

                        BREAK FROMTHE for  LOOP

                    END-IF

                ELSE

                END-IF

                IF FOUND is FALSE THEN

                    echo $file is NOT FOUND

                END-IF

            END-FOR

        END-IF

    END-FOR

END

I can't quite get my code to work. Like, I'll run it and get no echo. I also fear I am not commenting well or formatting well for general readability. If someone has some time and wants to relive their college freshmen days, can you point me in a good direction? Thank you.

Code:

#! /bin/sh 



#set a flag to check if you should search all for all occurances

#by default, you will only find the first occurance 



FINDALL=FALSE

        case $1 in

          -a)

            FINDALL=TRUE

                #throw away this argument

            shift

            ;;

        esac

for file

        do

        #if $file is a pathname

        case $file in

        */*)

        #if $file is executable and not a directory        

                if [ -x "$file" ]

                        then

                        if [ !-d "$file" ]

                                then

                                echo "$file"

                else

                        echo "$file NOT FOUND" 

                        fi

                fi

                ;;

        *)        #no / in the filename

                FOUND=FALSE

                ;;

        esac

#handle special cases of PATH

for P in `echo $PATH | sed -e 's/^:/.:/' -e 's/::/:.:/' -e 's/:$/:./' -e 's/:/ /g'`

        do                        #start the do loop through PATH        

        #test if $P/$file is a directory or executable

        case $file in

        *)

                if [ -f "$P/$file" ]

                        then

                        if [ !-d "$P/$file" ]

                                then

                                FOUND=TRUE

                                echo "$P/$file"

                        else [ FINDALL=FALSE ]

                        break 

                        fi

                fi

                ;;

        esac

        done

        if [$FOUND=FALSE]

                then

                echo "$file NOT FOUND" 

                fi

done

notKlaatu

03-02-2014 03:46 PM

I'm assuming the purpose of this script is to find whether or not the file issued as an argument actually exists or not..?

You're close, I think.

As a general rule, it's a good idea to "protect" your variables. So instead of writing things like

Code:

$P/$file

it is considered safer to write it:

Code:

${P}/${file}

And finally, I would say it's a good idea to insert "echo" statements A LOT when initially testing stuff. For me, these act a little like debugging statements, and it helps me know where exactly what is going on as the programme runs.

For instance, before entering an 'if' statement, precede it with a simple

Code:

echo "DEBUG: an if statement to test if file is exec or not"

or something like that. This way, you see what tests have passed and failed, and that ought to help you debug your own logic.

metaschima

03-02-2014 04:31 PM

Within the test command, the '=' and '==' are equivalent for bash. In fact, '=' is more compatible with sh.

You should certainly analyze the errors generated by the script. Also try using the 'bash -x' option to enter debug mode.
Also see:
http://www.cyberciti.biz/tips/debugg...ll-script.html

grail

03-02-2014 07:45 PM

As not mentioned earlier, please place code / data in [code][/code] tags so it is more readable and maintains your formatting.

notKlaatu

03-03-2014 12:14 AM

Quote:

Originally Posted by metaschima (Post 5127615)

I've edited my post just so it does not contain incorrect information for others who read this.

Thanks for the info, metaschima.

catkin

03-03-2014 07:02 AM

There are two unmatched fis and $file never has a value assigned to it.

Here's the script with indentation

Code:

#! /bin/sh



#set a flag to check if you should search all for all occurances

#by default, you will only find the first occurance



FINDALL=FALSE

case $1 in

    -a)

        FINDALL=TRUE

        #throw away this argument

        shift

    ;;

esac

for file

do

    #if $file is a pathname

    case $file in

        */*)

            #if $file is executable and not a directory

            if [ -x "$file" ]

            then

                if [ !-d "$file" ]

                then

                echo "$file"

            else

                echo "$file NOT FOUND"

            fi

            fi    # <<  Unmatched fi

            ;;

        *) #no / in the filename

            FOUND=FALSE

            ;;

    esac

    #handle special cases of PATH

    for P in `echo $PATH | sed -e 's/^:/.:/' -e 's/::/:.:/' -e 's/:$/:./' -e 's/:/ /g'`

    do #start the do loop through PATH

        #test if $P/$file is a directory or executable

        case $file in

            *)

                if [ -f "$P/$file" ]

                then

                    if [ !-d "$P/$file" ]

                    then

                    FOUND=TRUE

                    echo "$P/$file"

                else [ FINDALL=FALSE ]

                    break

                fi

                fi    # <<  Unmatched fi

                ;;

        esac

    done

    if [$FOUND=FALSE]

    then

        echo "$file NOT FOUND"

    fi

done

boygenuis

03-03-2014 02:24 PM

Thank you, all, for your help. I've tried to make my edits based on your recommendations and here's what I've got so far. Also, because I forgot to put it earlier, the objective for this program is, "Write a shell script to locate executable files. This script takes a list of file names from the command line and determines which would be executed had these names been given as commands."

Code:

#! /bin/sh -xv



#Student: boygenuis

#Course: Shell Scripting

#Assignment: Locating Executable Files

#Date: 03 MAR 2014



#set a flag to check if you should search all for

#all occurrences. By default, you will only find 

#the first occurrence



file="$1"

FOUND="$2"

 

$FINDALL = FALSE

        case $1 in

        -a)

                FINDALL = TRUE

                shift  #throw away this argument

                ;;

        esac

for file

        do

        #if $file is a pathname

        case $file in

        */*)

        #if $file is executable and not a

        #directory

                if [ -x "$file" -a ! -d "$file" ]

                        then

                        echo "$file"

                else

                        echo "$file NOT FOUND"

                fi

                ;;

#handle the special cases of PATH, start the DO loop

#through PATH, and test if $P/$file is a directory or

#executable

        *) 

                for P in `echo $PATH | sed -e 's/^:/.:/' -e 's/::/:.:/' -e 's/:$/:./' -e 's/:/ /g'`

                do 

                case $file in

                *)

                        if [ -f "$P/$file" -a ! -d "$P/$file" ]

                                then

                                FOUND = TRUE

                                        echo "$P/$file"

                        echo "DEBUG: Test if if [ FINDALL = FALSE ]"

                        if [ $FINDALL = FALSE ]

                                then

                                break

                                fi

                        fi

                        ;;

                esac

                done

                if [ $FOUND = FALSE ]

                        then

                        echo "$file NOT FOUND"

                fi

                ;;

        esac

done

notKlaatu

03-03-2014 04:13 PM

It appears to work for me, with a few slight changes:

Line 15

Code:

$FINDALL = FALSE

should read

Code:

FINDALL=FALSE

and Line 18

Code:

FINDALL = TRUE

should read

Code:

FINDALL=TRUE

Other wise it did seem to work insofar as I entered

Code:

boygenius.sh python

and got

Code:

/usr/bin/python

in return. Didn't really do any testing beyond that.

As grail points out though, you really should use this markup when pasting in code:
[code]
code goes here
[/code]

grail

03-03-2014 08:44 PM

It is forgivable to have not done so the first time, but to ignore the request and do it again is not. Please go back and edit both posts and place your code in code tags.

I for one will not read something that is not formatted and as was pointed out by catkin, this simple process would have led you to find easily fixable issues.

TB0ne

03-04-2014 09:39 AM

Regardless of the post formatting, the OP has shown adherence to the forum rules about posting homework, has shown effort of their own, and has been polite throughout. More posters should follow that example, in my opinion.

grail

03-04-2014 10:58 AM

And I am not chiding them for their good effort, but unfortunately with my old eyes the lack of contrast and formatting makes it difficult to assist :(

metaschima

03-04-2014 11:02 AM

Indent is also extremely useful in looking at code. If it's not in code tags, I tend to not look too closely at it.

PTrenholme

03-04-2014 01:54 PM

Re the post #8 by notKlaatu, one point made is that spaces are "tokenizers" in bash and Posex-compliant variants. (bash, itself, is not Posix-compliant.) Thus A = B is three "tokens," whilst A=B is one "token," and interpreted as an implicit let command.

The other point is that $ is a substitution command, and a command can't occur as the target of an assignment.

szboardstretcher

03-04-2014 02:00 PM

Thats a great explanation.

To add to that... the reason bash tokenizes them using spaces is a variable called IFS which defaults to " \t\n" easier read as "(space)(tab)(newline)"

TB0ne

03-04-2014 02:06 PM

Quote:

Originally Posted by grail (Post 5128766)

And I am not chiding them for their good effort, but unfortunately with my old eyes the lack of contrast and formatting makes it difficult to assist :(

Believe me...I agree with you; I don't wear bifocals for fun. :) But I did want to give credit to the OP, especially given the MANY homework requests we see that are barely intelligible and/or posted verbatim from a book, with no effort at all.

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