SSH session - why bash FOR loop is not even showing value and also using LOCAL machine

Question

I'm running this SSH command:

ssh -p 2001 -q [email protected] \
  " echo
    echo Now On Target Server, I see
    ls -l /tmp/Folder-1.1.0.1053/*
    for v in A B C ; do
      echo === $v===
    done
    echo
    for f in /tmp/Folder-1.1.0.1053/* ; do
      echo File is == $f
    done
  "

and it's printing this:

Now On Target Server, I see
-rw------- 1 root root 159790 Jan 23 17:03 /tmp/Folder-1.1.0.1053/file1-1.8.30.tar.gz
-rw------- 1 root root 116731 Jan 23 17:03 /tmp/Folder-1.1.0.1053/file2-2.7.49.tar.gz
=== ===
=== ===
=== ===

File is ==
File is ==

I have a few questions:

Why doesn't the first for loop print the values of the variable $v?
Why (when I see the target server have valid files in /tmp/<folder>) the second for loop did not print the values of the $f variable?
How can I get the second for loop to print the two .tar.gz files?
I tried $(...) or using back quotes to wrap the input values (for for loop) in the second for loop but it has no effect. For some reason, it's expecting those * files using the local machine. Why?

If it's relevant, my Bash version is "GNU bash, version 4.1.2(1)-release (x86_64-redhat-linux-gnu)", and my Linux version is "Red Hat Enterprise Linux Server release 6.9 (Santiago)".

AKS · Accepted Answer · 2019-01-30 15:15:48Z

3

Because you're wrapping your ssh command with double quotes, all your $ variables are being interpolated by the local shell before going over the wire to the remote shell. Either use single quotes or escape your $ sigils.

Ex:

ssh -p 2001 -q [email protected] "echo; echo Now On Target Server, I see; ls -l /tmp/Folder-1.1.0.1053/*; for v in A B C; do echo === \$v===; done; echo; for f in /tmp/Folder-1.1.0.1053/*; do echo File is == \$f; done"

or

ssh -p 2001 -q [email protected] 'echo; echo Now On Target Server, I see; ls -l /tmp/Folder-1.1.0.1053/*; for v in A B C; do echo === $v===; done; echo; for f in /tmp/Folder-1.1.0.1053/*; do echo File is == $f; done'

See very Important note below. Escape only the variable created and used within the SSH session (ex: for loop here) or any where inside SSH session. Do NOT escape a variable which was defined in your script and outside of SSH session, ex: as used in the command / input part in for loop. i.e. for v in ${staging_area}/*.tar.gz; do echo ==\$v;done" here I escaped \$v but did not escape ${staging_area}

edited Jan 30, 2019 at 15:15

AKS

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answered Jan 23, 2019 at 18:13

Tanktalus

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3 Comments

AKS Over a year ago

Zeeesus! Thanks.

AKS Over a year ago

So very important NOTE here.. If using double quote with SSH, make sure a user is escaping $v or $f type of variables i.e. any variable within the for or similar loop. You Must NOT backslash variables using in the conditional / command part of the for loop itself. Ex: for v in ${staging_area}/*.tar.gz; do echo \$v; done here I didn't escape staging_area variable or it'll leave //*.tar.gz as for loop's input.

Tanktalus Over a year ago

Don't keep adding to the answer - your comments are fine, they'll still be readable to later people.

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