Bash script launches the first switch-case loop option again - bash

Question

Here's the code:
#!/bin/bash
function print_help() {
echo "Just a pile of echos; no other logic here"
}
die() {
printf '%s\n' "$1" >&2
exit 1
}
IpAddress=
SourceDir=
DestDir=
backup=0
restore=0
while :; do
case $1 in
''|-h|\?|--help) print_help
exit 0
;;
-b|--backup)
if [ $restore -eq 0 ]; then
backup=1
echo "Taking backup..."
else
die "ERROR: Can't perform backup and restore at the same time."
fi
;;
-r|--restore)
if [ $backup -eq 0 ]; then
restore=1
echo "Restoring backup..."
else
die "ERROR: Can't perform backup and restore at the same time."
fi
;;
--ip)
if [ "$2" ]; then
ip=$2
shift
else
die 'ERROR: "--ip" requires a non-empty option argument.'
fi
;;
--ip=?*)
IpAddress=${1#*=}
echo "IP Address: $IpAddress"
;;
--source-dir=?*)
SourceDir=${1#*=}
if [ -d "$SourceDir" ]; then
echo "Source Directory: $SourceDir indeed exists"
else
die "ERROR: $SourceDir doesn't exist."
fi
;;
--source-dir=)
die 'ERROR: "--source-dir" requires a non-empty argument.'
;;
--dest-dir=?*)
DestDir=${1#*=}
if [ -w "$DestDir" ]; then
echo "Destination Directory: $DestDir indeed exists and is writable."
else
die "ERROR: $DestDir doesn't exist or is not writable for current user."
fi
;;
--dest-dir=)
die 'ERROR: "--dest-dir" requires a non-empty argument.'
;;
--)
shift
break
;;
-?*)
printf 'Warning: Unknown option (ignoring): %s\n' "$1" >&2
;;
*)
break
esac
shift
done
So far, I've tested two use cases, with directories:
/tmp/back/ (in which user has no read permissions) and
/tmp/back2/ (which fully belongs to the user).
The 1st option launched correctly prints the error message:
$ ./backup.sh -b --source-dir=/opt/ --dest-dir=/tmp/back/
Taking backup...
Source Directory: /opt/ indeed exists
ERROR: /tmp/back/ doesn't exist or is not writable for current user.
Meanwhile the 2nd option confirms that data is OK, and seems to come back to the print_help case:
$ ./backup.sh -b --source-dir=/opt/ --dest-dir=/tmp/back2/
Taking backup...
Source Directory: /opt/ indeed exists
Destination Directory: /tmp/back2/ indeed exists and is writable.
backup.sh: backup.sh <-b|r> [-h] [server IP] <source dir> <dest dir>
Take or restore a backup of files.
What should be corrected here in order to exit the script after all options are checked one time?

Answer 1

The problem is that your while loop is an infinite loop, and you only break out of that loop in two of your 12 cases, or when an error occurs. So unless the code encounters those two cases, or an error, it will keep iterating even when there are no more parameters to read. When all of the parameters have been shifted, $1 will evaluate to an empty string, which is explicitly listed in your first case (''|-h|\?|--help) print_help), resulting in the help message.
The solution is to test for the existence of parameters in your while loop:
if [ $# -eq 0 ]; then
print_help
exit 1
fi
while [ $1 -gt 0 ]; do
case $1 in
-h|\?|--help) print_help
...
done
That way, when the last parameter has been shifted, the loop will end.

Answer 2

When all args ended $1 is '' that is why it comes back to the print_help
What should be corrected here in order to exit the script after all
options are checked one time?
Change print_help pattern to *) and '') should be exit 0
But better change while condition to:
while [[ $1 ]]; do
...
done
And this check could be added at the beginning of the script:
[[ $1 ]] || print_help
to print help message and exit if no args passed to the script.

Answer 3

Remove '' from the case statement and test if there are no arguments before the loop:
[[ $1 ]] || { print_help ; exit 0 ; }
while :; do
case $1 in
-h|\?|--help) print_help
exit 0
;;