How do I iterate over a local array in a remote ssh bash command

Question

I need to perform several copy commands on a remote location (using ssh "cp blah blah2"). Instead of having a separate ssh connection for each command, I would like to do something like:

dirs=(dir1 dir2 dir3)
for dir in ${dirs[*]} ; do echo $dir; done
ssh user@server "for dir in ${dirs[*]}; do echo $dir; cp some/file.txt /home/user/$dir/; done"

But even though the first echo prints all three dirs, the echos performed on the remote server are all equal to the last dir value ("dir3"). I don't understand what I'm doing wrong, or why it's printing three echos (and doing three copies), when it's only using the same value. I guess it has something to do with when the variables are expanded (locally or remotely)...

I've tried using dirs="dir1 dir2 dir3", @ instead of *, quotings, but I haven't been able to find a combination that works.

Anyone have any experience with this problem? :)

Cheers, Svend.

Francisco R · Accepted Answer · 2011-06-17 06:55:05Z

4

The for loop you execute before calling ssh creates a $dir varible and your shell expands it, so you are actually executing:

    ssh user@server "for dir in dir1 dir2 dir3; do echo dir3; cp some/file.txt /home/user/dir3/; done"

You should escape $ to avoid shell expansion. Try:

dirs="dir1 dir2 dir3"
ssh user@server "for dir in $dirs ; do echo \$dir; cp some/file.txt /home/user/\$dir/; done"

In this example, $dirs is a local variable and $dir is a remote variable. Your shell will replace $dirs in your command BEFORE executing ssh, so you will be really executing:

ssh user@server "for dir in dir1 dir2 dir3; do echo \$dir; cp some/file.txt /home/user/\$dir/; done"

edited Jun 17, 2011 at 6:55

answered Jun 16, 2011 at 15:44

Francisco R

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4 Comments

Svend Hansen Over a year ago

I would have thought the first one would definitely work (while not being ideal, as my dir array may be quite large), but it doesn't seem to. I even tried this: ssh user@server "for dir in dir1 dir2 dir3; do echo $dir; done" and that gives the same result (dir3\ndir3\ndir3)... :(

Francisco R Over a year ago

To avoid shell intereferences, escape your variables with a backslash before each dollar as in my examples. $dir --> \$dir

Svend Hansen Over a year ago

Sorry, didn't spot that :) Thank you!

David Doria Over a year ago

@FranciscoR - That seems to work with the array loop syntax: myArray="onething anotherthing"; ssh thufirg-0105 "for myValue in ${myArray[@]}; do echo \$myValue; done;" but it does not seem to work when using a loop counter?: myArray="onething anotherthing"; ssh thufirg-0105 "for ((i=0; i<2; i++ )); do echo ${myArray[\$i]}; done;" ?

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