while-read loop broken on ssh-command

Question

I have a bash-script that moves backup-files to the remote location. On few occasions the temporary HDDs on the remote server had no space left, so I added a md5 check to compare local and remote files. The remote ssh breaks however the while-loop (i.e. it runs only for first item listed in dir_list file).

# populate /tmp/dir_list
(while read dirName
  do
  # create archive files for sub-directories
  # populate listA variable with archive-file names
...
     for fileName in $listA; do
        scp /PoolZ/__Prepared/${dirName}/$fileName me@server:/archiv/${dirName}/
        md5_local=`md5sum /PoolZ/__Prepared/${dirName}/${fileName} | awk '{ print $1 }'`
        tmpRemoteName=`printf "%q\n" "$fileName"` # some file-names have strange characters
        md5_remote=`ssh me@server 'md5sum /archiv/'${dirName}'/'$tmpRemoteName | awk '{ print $1 }'`
        if [[ $md5_local == $md5_remote ]]; then
          echo "Checksum of ${fileName}: on local ${md5_local}, on remote ${md5_remote}." 
          mv -f /PoolZ/__Prepared/${dirName}/$fileName /PoolZ/__Backuped/${dirName}/
        else
          echo "Checksum of ${fileName}: on local ${md5_local}, on remote ${md5_remote}."  
          # write eMail
        fi
     done
  done) < /tmp/dir_list

When started the script gives the same md5-sums for the first directory listed in dir_list. The files are also copied both local and remote to expected directories and then script quits.

If I remove the line:

md5_remote=`ssh me@server 'md5sum /archiv/'${dirName}'/'$tmpRemoteName | awk '{ print $1 }'`

then apparently the md5-comaprison is not working but the whole script goes through whole list from dir_list.

I also tried to use double-quotes:

md5_remote=`ssh me@server "md5sum /archiv/${dirName}/${tmpRemoteName}" | awk '{ print $1 }'`

but there was no difference (broken dirName-loop).

I went so far, that I replaced the md5_remote... line with a remote ls-command without any shell-variables, and eventually I even tried a line without setting value to the md5_remote variable, i.e.:

ssh me@server "ls /dir/dir/dir/ | head -n 1"

Every solution that has a ssh-command breaks the while-loop. I have no idea why ssh should break bash-loop. Any suggestion are welcomed.

Also, doesn't the exit status of scp tell you if there was an error (such as the remote device running out of space)? — chepner
– chepner, Commented Nov 28, 2019 at 14:51

Kris_R · Accepted Answer · 2019-11-28 14:14:52Z

2

I'm plainly stupid. I found just answer on — what a surprise — stackoverflow.com.

ssh breaks out of while-loop in bash

As suggested I added a pipe to /dev/null and it works now:

md5_remote=`ssh me@server 'md5sum /archiv/'${dirName}'/'$tmpRemoteName < /dev/null | awk '{ print $1 }'`

answered Nov 28, 2019 at 14:14

Kris_R

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1 Comment

Ouss Over a year ago

also ssh -n would have worked.

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