ssh breaks out of while-loop in bash [duplicate]

Question

I use this bash-code to upload files to a remote server, for normal files this works fine:

for i in `find devel/ -newer $UPLOAD_FILE` do     echo "Upload:" $i     if [ -d $i ]     then         echo "Creating directory" $i         ssh $USER@$SERVER "cd ${REMOTE_PATH}; mkdir -p $i"         continue     fi     if scp -Cp $i $USER@$SERVER:$REMOTE_PATH/$i     then         echo "$i OK"     else         echo "$i NOK"         rm ${UPLOAD_FILE}_tmp     fi done 

The only problem is that for files with a space in the name, the for-loop fails, so I replaced the first line like this:

find devel/ -newer $UPLOAD_FILE | while read i do     echo "Upload:" $i     if [ -d $i ]     then         echo "Creating directory" $i         ssh $USER@$SERVER "cd ${REMOTE_PATH}; mkdir -p $i"         continue     fi     if scp -Cp $i $USER@$SERVER:$REMOTE_PATH/$i     then         echo "$i OK"     else         echo "$i NOK"         rm ${UPLOAD_FILE}_tmp     fi done 

For some strange reason, the ssh-command breaks out of the while-loop, therefore the first missing directory is created fine, but all subsequent missing files/directories are ignored.

I guess this has something to do with ssh writing something to stdout which confuses the "read" command. Commenting out the ssh-command makes the loop work as it should.

Does anybody know why this happens and how one can prevent ssh from breaking the while-loop?

Answer 1

The problem is that ssh reads from standard input, therefore it eats all your remaining lines. You can just connect its standard input to nowhere:

ssh $USER@$SERVER "cd ${REMOTE_PATH}; mkdir -p $i" < /dev/null 

You can also use ssh -n instead of the redirection.

Answer 2

Another approach is to loop over a FD other than stdin:

while IFS= read -u 3 -r -d '' filename; do   if [[ -d $filename ]]; then     printf -v cmd_str 'cd %q; mkdir -p %q' "$REMOTE_PATH" "$filename"     ssh "$USER@$SERVER" "$cmd_str"   else     printf -v remote_path_str '%q@%q:%q/%q' "$USER" "$SERVER" "$REMOTE_PATH" "$filename"     scp -Cp "$filename" "$remote_path_str"   fi done 3< <(find devel/ -newer "$UPLOAD_FILE" -print0) 

The -u 3 and 3< operators are critical here, using FD 3 rather than the default FD 0 (stdin).

The approach given here -- using -print0, a cleared IFS value, and the like -- is also less buggy than the original code and the existing answer, which can't handle interesting filenames correctly. (Glenn Jackman's answer is close, but even that can't deal with filenames with newlines or filenames with trailing whitespace).

The use of printf %q is critical to generate commands which can't be used to attack the remote machine. Consider what would happen with a file named devel/$(rm -rf /)/hello with code which didn't have this paranoia.