Bash script: dealing with spaces when running indirectly commands

Question

I have been struggling for a while with the folllowing problems I have written scripts in which any command run is first put into a string, and then executed. That way, the command is written only once and it can be analysed, displayed, used several times. It works fine most of the time but not in the following detailed cases below. So if any of you can help, I would be more then happy ;) I must admit I have always struggle to understand the way script works when dealing with variables containing quotes and spaces, so if you know of a good tutorial ...

Case 1: mkdir command

dir="/tmp/Mytests/DirWith2 spaces 2"
cmdToRun="mkdir -p ${dir}"
echo "Running [${cmdToRun}]"
${cmdToRun} # <= this does not work, OK it seems normal !

cmdToRun="mkdir -p """${dir}""""
${cmdToRun} # <= this does not work either !

cmdToRun="mkdir -p \"${dir}\""
${cmdToRun} # <= this does not work either !

Case 2: rsync command

rsync_cmd="rsync -avz --stats " 
rsync_destinationBaseDir="/tmp/ToTestRsync"
ListOfDirToSynchronize=( \
"/opt/dir1/subdir1" "/opt/dir1space 1/subdir1" "/opt/dir1space 1/subdir1space 1" )
rsync_host_from="root@SRV1:" 
A loop on the directories in my ListOfDirToSynchronize
{
  SourceDir="${ListOfDirToSynchronize[$i]}"  
  ( # here we start a subshell to run // rsyncsto speed-up the whole process
    cmdToRun="${rsync_cmd} ${rsync_host_from}'${SourceDir}/' ${rsync_destinationBaseDir}${SourceDir}"
    funcLog " | INFO | Directories synchronisation | SubprocessID [${subProcessID}] | running command [${cmdToRun}]"
    ${cmdToRun} >> ${LOG_FILE} 2>&1 #<== this does not work when spaces in the directories
  ) # end of subshell
} # end of the loop

Answer 1

Short answer: see BashFAQ #050.

Long answer: usually, the best way to do this is by putting commands in arrays rather than simple variables (eval is not recommended -- it tends to create new and dangerous bugs). Here's case 1 done array-style:

dir="/tmp/Mytests/DirWith2 spaces 2"
cmdToRun=(mkdir -p "${dir}")  # Note double-quotes to preserve spaces within $dir
"${cmdToRun[@]}"  # This is the standard idiom for expanding an array preserving both spaces and word breaks

Case 2:

rsync_cmd=(rsync -avz --stats)
rsync_destinationBaseDir="/tmp/ToTestRsync"
ListOfDirToSynchronize=( \
  "/opt/dir1/subdir1" "/opt/dir1space 1/subdir1" "/opt/dir1space 1/subdir1space 1" )
rsync_host_from="root@SRV1:" 
# A loop on the directories in my ListOfDirToSynchronize
for SourceDir in "${ListOfDirToSynchronize[@]}"; do
  ( # here we start a subshell to run // rsyncsto speed-up the whole process
    cmdToRun=("${rsync_cmd[@]}" "${rsync_host_from}${SourceDir}/" "${rsync_destinationBaseDir}${SourceDir}")
    funcLog " | INFO | Directories synchronisation | SubprocessID [${subProcessID}] | running command [${cmdToRun[*]}]"
    "${cmdToRun[@]}" >> ${LOG_FILE} 2>&1 #<== this does not work when spaces in the directories
  ) # end of subshell
done # end of the loop

Note that in the log entry I used ${cmdToRun[*]} instead of ${cmdToRun[@]}, so it'll separate the array entries with spaces rather than treating them as separate arguments to funcLog. This means the log is ambiguous (you can't tell spaces within filenames from spaces between filenames); if this is a problem, use $(printf " %q" "${cmdToRun[@]}") instead, and it'll add quotes/escapes/etc for spaces within filenames.

Answer 2

The eval command is your friend:

dir="/tmp/Mytests/DirWith2 spaces 2"

cmdToRun="mkdir -p \"${dir}\""
eval "${cmdToRun}"

And:

cmdToRun="${rsync_cmd} ${rsync_host_from}'${SourceDir}/' '${rsync_destinationBaseDir}${SourceDir}'"
funcLog ...
eval "${cmdToRun}" >> "${LOG_FILE}" 2>&1