UNIX for Dummies Questions & Answers

Hello All,
I'll try to get it right this time lol

I am trying to do some validation on my script which renames files.
The ones i am struggling with are:


e.g.

1. myscript myfile myfile2 (so my script changes myfile to myfile2 if myfile exists)
output : myfile does not exist

2. myscript myfile myfile2 blurb
cannot have anything after rename

3. myscript myfile
must have name to rename2

Hope that makes sense. I'll put a bit of my code in to try to make it clearer

case $# in
0) echo "nothing has been entered"
exit
;;
1) echo "file none existent"
exit
;;
2) echo "dosRename: $file: Can't have anything after target"
exit
;;
3) echo "no new name"
exit
;;
*)

The existence test looks like this:

Code:

test -e "$1" || die "$1 does not exist"

You might as well also check that the file is readable by the user.

Code:

test -r "$1" || die "$1 is not readable"

(The die function is not a standard shell command; implementing that is left as an exercise.)

You already check the number of arguments; if it's 3 or larger, that's this case.

And this is when $# is 1.

This is not correct; you want exactly two arguments, if I understand your sketch correctly.

Hi,
Thanks for the reply.
I am still a bit puzzled though. The code for the existing file i don't understand how to implement this. Here is the code i have already:

#!/bin/bash

case $# in
0) echo "Usage: Myscript file1 file2"
exit
;;
So here is where i want to code the file existence and other arguments I thought it would go something like this but this doesn't work. Am i on the right lines?
test -e "$1") echo "file dosent exist"
;;
exit;
*) for file
Then my code for the rename goes here


Also the answer to the last question is true i only want exactly two arguements but i want a message if no target is specified and a different message if extra text is entered after the target.
If that makes sense?

Code:

case expression in pattern1) handle pattern1 ;; pattern2) etc;; esac

... compares expression to pattern1, pattern2, etc until a match is found, or falls through.

Your case statement is examining the expression $# and you certainly don't want to compare that to the pattern 'test -e "$1"' (syntax problems notwithstanding). Create a new conditional for that.

Code:

#!/bin/bash

case $# in 2);; *) echo "Usage: $0 file1 file2" >&2; exit 1;; esac

if ! test -e "$1" ; then
  echo "$0: file $1 does not exist" >&2
  exit 2
fi

for file ...

Note that I changed the first case to require exactly two files, based on your syntax message. If $# is 2, the first pattern matches; if not, it falls through to the second pattern, which matches everything else, and causes the script to exit.

Also, take care to set the exit code to signal error conditions; one day, you will be glad you did. (0 means success, everything else is an error. It makes sense to set different exit codes for different error conditions so you can tell which one fired programmatically as well as by examining what the script printed.)

The technique to exit early in case of some error allows you to avoid nesting the conditionals very deep. If you pass all the conditions, you fall through to the main functionality; otherwise, report an error and exit early.

That's great i understand a lot better now
My usage is a lot better now i have done what you said but it does not like end of the if

syntax error near unexpected token `fi'

Works here, are you sure you copy+pasted correctly?

Yeah i got it working eventually. However when i try to use my script now it is telling me incorrect use.
So i type in
myscript file.* test.*
and i get "usage file1 file2" as if i am using it incorrectly. Is this becasue my script is for file names AND extensions?

If i wanted to add another statement would i add to this to the case i already have?

i.e.

case $# in 2);; *) echo "Usage: $0 file1 file2" >&2; exit 1;;
'..') echo "cannot have more than one dot" exit ;;
another case) echo "blah blah blah" exit ;; esac

if ! test -e "$1" ; then
echo "$0: file $1 does not exist" >&2
exit 2
fi

would this be correct?