SSH session - why bash FOR loop is not even showin

问题:

I'm running this SSH command:

ssh -p 2001 -q root@12.13.14.15 \
  " 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:

1. Why doesn't the first for loop print the values of the variable $v?
2. 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?
3. How can I get the second for loop to print the two .tar.gz files?
4. 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)".

回答1:

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 root@12.13.14.15 "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 root@12.13.14.15 '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}