BASH Scripting assistance needed

Question

Well, I am currently a novice shell scripter. I have a basic knowledge of other programming languages such as Javascript for HTML, JScript, VB.NET, and C++. (C++ Not so much, just dipped my feet in the water for that). Most recently, my recent project has been attempting to learn as much as I can about Bash shell scripting. The current issue is understanding status error codes, as well as checking if certain parameters contain directories or if it exists at all. I am working from a book, with tutorials and review questions. Unfortunately there is no answer key, or even hints for that matter.

Display an error message and exit with status 1 if no parameters are given
Display an error message and exit with status 2 if source is not a directory
Display an error message and exit with status 3 if destination does not exist or is not a directory

The above is what I must do, so far the first one I believe I have done correctly, if not please, correct me, or guide me in the proper direction. As I learn best when samples are given, I thought I would ask for assistance.

if [ $? ]; then
  echo "You must supply at least one parameter"
  exit 1
fi
  #The above is the part I am pretty sure is correct.


if [ $? -d $directory "$1" ]; then
  echo "$directory is not a directory"
  exit 2
fi
#The above was self written. I am almost positive it is wrong.

if [ $? -lt 2 ]; then
  set "$1" .pwd
fi
#the above was given to me from the book as a reference point to start (tutorial)

Cfreak · Accepted Answer · 2010-11-24 15:13:27Z

2

$? is the return code of a command you execute. Maybe you are thinking it's a return code of the current script. In any case it's not doing what you think it's doing.

All of my examples assume your command is run like so: script [source] [destination]

Error message if no parameters are given:

if [ ! "$#" ]; then
     echo "please supply a parameter"
     exit 1
fi

Display error if source is not a directory

if [ ! -d "$1" ]; then
     echo "$1 is not a directory"
     exit 2
fi

Display error if destination doesn't exist or isn't a directory

if [ ! -d "$2" ]; then
     echo "$2 doesn't exist or isn't a directory"
     exit 3
fi

edited Nov 24, 2010 at 15:13

answered Nov 23, 2010 at 22:54

Cfreak

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6 Comments

jilles Over a year ago

There should be a space between if and [. $1 and $2 should be quoted to avoid field splitting and pathname generation. || separates commands so you need if [ ! -e "$2" ] || [ ! -d "$2" ]; then (although the -e test is redundant here, -d already returns false if it does not exist).

Michael Ferro Over a year ago

Wow, now that you state it, I should have gotten it on my own. I have not even attempted to try it on my own shell, but just from looking at it, it appears to be 100% correct. I appreciate the fast response. Thank you.

Cfreak Over a year ago

@user518073 - no problem. Make sure to check the edits I did per @jiles suggestions.

Michael Ferro Over a year ago

I did not even notice the mistakes, I typed them properly, the spaces as well as the "$1", however, the redundant -e has been noted.

Ignacio Vazquez-Abrams Over a year ago

Checking for an empty $1 can be tricked into a false negative (even though an empty parameter is not always useful). It's best to check $# explicitly.

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