This question already has answers here:
is it possible to use variables in remote ssh command?
(2 answers)
Closed 4 years ago.
in a bash script i try to do:
ssh -n $username#server2 "rm ${delete_file}"
but always get the error:
rm: missing operand
when I
> echo $delete_file
> /var/www/site/myfile.txt
I get the correct path.
What am i doing wrong?
Could it be that in your case, $delete_file is set on the remote host and not on your current machine?
If you want $delete_file to be expanded on the remote side (i.e., after ssh'ing into server2), you have to use single quotes:
ssh -n $username#server2 'rm ${delete_file}'
Other than that, do you set the value of delete_file in the same script (before ssh'ing), or before invoking your script? If latter is the case, it can't work: Variables are not propagated to scripts called by the current script/session.
You could do the following about it:
delete_file=<your-value> ./ssh-script
or:
delete_file=<your-value>
export delete_file
./ssh-script
As it turns out this last option was the problem, let me elaborate on best practices:
Better than setting environment variables would be the usage of positional parameters.
#!/bin/bash
# $1: file to delete
delete_file=${1:?Missing parameter: which file for deletion?}
ssh -n $username#server2 "rm ${delete_file}"
Usage of the script is now as simple as:
./ssh-script <your-file-for-deletion>
This way, you don't have to remember which variable is exactly expected by the script when calling it - simply call the script with a positional parameter.
As a bonus, the example uses parameter expansion to check for not-set or empty parameters:
delete_file=${1:?Missing parameter: which file for deletion?}
Whenever $1 happens to be unset or empty, the scripts exits immediately with exit code 1 and prints given message to stderr.
Related
Say I start with the following statement, which echo-s a string into the ether:
$ echo "foo" 1>/dev/null
I then submit the following pipeline:
$ echo "foo" | cat -e - 1>/dev/null
I then leave the process out:
$ echo "foo" | 1>/dev/null
Why is this not returning an error message? The documentation on bash and piping doesn't seem to make direct mention of may be the cause. Is there an EOF sent before the first read from echo (or whatever the process is, which is running upstream of the pipe)?
A shell simple command is not required to have a command name. For a command without a command-name:
variable assignments apply to the current execution environment. The following will set two variables to argument values:
arg1=$1 arg3=$3
redirections occur in a subshell, but the subshell doesn't do anything other than initialize the redirect. The following will truncate or create the indicated file (if you have appropriate permissions):
>/file/to/empty
However, a command must have at least one word. A completely empty command is a syntax error (which is why it is occasionally necessary to use :).
Answer summarized from Posix XCU§2.9.1
I am trying to login on one of the remote server(Box1) and trying to read one file on remote server(Box1).
That contain the another server(Box2) details, base upon that details I have to come back to the local server and ssh to another server(Box2) for some data crunching. and so on.....
ssh box1.com << EOF
if [[ ! -f /home/rakesh/tomar.log ]]
then
echo "LOG file not found"
else
echo " LOG file present"
export server_node1= `cat /home/rakesh/tomar.log`
fi
EOF
ssh box2.com << EOF
if [[ ! -f /home/rakesh/tomar.log ]]
then
echo "LOG file not found"
else
echo " LOG file present"
export server_node2= `cat /home/rakesh/tomar.log`
fi
EOF
but I am not getting value of "server_node1" and "server_node2" on local machine.
any help would be appreciated.
Just like bash -c 'export foo=bar' cannot declare a variable in the calling shell where you typed this, an ssh command cannot declare a variable in the calling shell. You will have to refactor so that the calling shell receives the information and knows what to do with it.
I agree with the comment that storing a log file in a variable is probably not a sane, or at least elegant, thing to do, but the easy way to do what you are attempting is to put the ssh inside the assignment.
server_node1=$(ssh box1.com cat tomar.log)
server_node2=$(ssh box2.com cat tomar.log)
A few notes and amplifications:
The remote shell will run in your home directory, so I took it out (on the assumption that /home/rt9419 is your home directory, obviously).
In case of an error in the cat command, the exit code of ssh will be the error code from cat, and the error message on standard error will be visible on your standard error, so the echo seemed quite superfluous. (If you want a custom message, variable=$(ssh whatever) || echo "Custom message" >&2 would do that. Note the redirection to standard error; it doesn't seem to matter here, but it's good form.)
If you really wanted to, you could run an arbitrarily complex command in the ssh; as outlined above, it didn't seem necessary here, but you could do assigment=$(ssh remote 'if [[ things ]]; then for variable in $(complex commands to drive a loop); do : etc etc; done; fi; more </dev/null; exit "$variable"') or whatever.
As further comments on your original attempt,
The backticks in the here document in your attempt would be evaluated by your local shell before the ssh command even ran. There are separate questions about how to fix that; see e.g. How have both local and remote variable inside an SSH command. but in short, unless you absolutely require the local shell to be able to modify the commands you send, probably put them in single quotes, like I did in the silly complex ssh example above.
The function of export is to make variables visible to child processes. There is no way to affect the environment of a parent process (short of having it cooperate and/or coordinate the change, as in the code above). As an example to illustrate the difference, if you set PERL5LIB to a directory with Perl libraries, but fail to export it, the Perl process you start will not see the variable; it is only visible to the current shell. When you export it, any Perl process you start as a child of this shell will also see this variable and the value you assigned. In other words, you export variables which are not private to the current shell (and don't export private ones; aside from making sure they are private, this saves the amount of memory which needs to be copied between processes), but that still only makes them visible to children, by the design of the U*x process architecture.
You should get back the file from box1and box2 with an scp:
scp box1.com:/home/rt9419/tomar.log ~/tomar1.log
#then you can cat!
export server_node1=`cat ~/tomar1.log`
idem with box2
scp box2.com:/home/rt9419/tomar.log ~/tomar2.log
#then you can cat!
export server_node2=`cat ~/tomar2.log`
There are several possibilities. In your case, you could on the remote system create a file (in bash syntax), containing the assignments of these variables, for example
echo "export server_node2='$(</home/rt9419/tomar.log)'" >>export_settings
(which makes me wonder why you want the whole content of your logfile be stored into a variable, but this is another question), then transfer this file to your host (for example with scp) and source it from within your bash script.
This question already has an answer here:
bash - export doesn't work
(1 answer)
Closed 7 years ago.
I am running the following simple code in a shell script , but it seems like it cant export the variable :
#!/bin/bash
echo -n "Enter AWS_ACCESS_KEY_ID: "
read aws_access_key
export AWS_ACCESS_KEY_ID=$aws_access_key
After that I take the input from the user ,but when I run echo $AWS_ACCESS_KEY_ID I get a blank value .
Run your script in the current shell by using:
source your-script # this runs your-script in the existing shell
...or, if using a POSIX shell...
. your-script # likewise; that space is intentional!
not
./your-script # this starts a new shell just for `your-script`; its variables
# are lost when it exits!
...if you want variables it sets to be available to the shell that calls it.
To be clear, export puts a variable in the current process's environment -- but environment variables are propagated down to child processes, not up to parent processes.
Now, if your goal is to define an interactive command that's easy to call, you might want to consider an entirely different approach altogether -- putting a function in your .bashrc:
awsSetup() {
echo -n "Enter AWS_ACCESS_KEY_ID: "
read && [[ $REPLY ]] && export AWS_ACCESS_KEY_ID=$REPLY
}
...after which the user with this in their .bashrc can run awsSetup, which will run in the current shell.
I am passing variable from one shell script to another which is being executed on another remote server.
Script 1
echo "Identification No."
read id
export id
ssh atul#10.95.276.286 'bash -s' < data_file.sh
Script 2
echo "ID is ---- "$id
cd /abc/xyz/data/
cat data_abcxyz.txt|grep '|$id|'|wc -l
By this way I am not able to get any output even the id is also null in the second script.
I have also tried
ssh atul#10.95.276.286 'bash -s' < data_file.sh "$id"
But got no output.
Any help on this is greatly appreciated. I am using unix AIX.
export on one host is absolutely not going to affect an entirely different host... it doesn't even affect another shell running on the current host.
Your second attempt is better and might even work if your script were checking for positional arguments but it isn't. (It might not even work in that case as I'm not at all sure that the command line argument would make it through to the script through ssh and bash -s.
You might be able to do something more like:
ssh atul#10.95.276.286 "bash -s $id" < data_file.sh
to pass the argument to the remote bash directly but your script would still need to use positional arguments and not expecting named variables to already exist.
Exporting won't have any effects on the environment of remote scripts.
You can set up a remote script's environment by specifying the env variables on the command line before the actual command, which you can btw use for local commands too.
ssh atul#10.95.276.286 "id=$id bash -s" < data_file.sh
If you pass "$id" this way:
ssh atul#10.95.276.286 'bash -s' < data_file.sh "$id"
It'll be your script's first parameter, AKA "$1" and you'll be able to access it from your script that way.
Note that '|$id|' in your "Script 2" will be interpreted as a literal string, since you're using single quotes.
I am writing a simple bash script (checkServs.sh) that will ssh into a list of servers and perform a health check on them.
I keep getting errors on the following line:
SERVERS=(blah1.example.com blah2.example.com blah3.example.com blah4.example.com)
Error is:
checkServs.sh: 3: checkServs.sh: Syntax error: "(" unexpected
I've checked online examples and this seems correct, isn't it? Thanks in advance!
I don't know about the syntax error, but this should work:
SERVERS="blah1.example.com blah2.example.com blah3.example.com blah4.example.com"
for server in $SERVERS
do
echo $server
done
EDIT: As noted by Jonathan Leffler in a comment, maybe you are not running the script with bash. Other shells, such as dash, may not recognize the array syntax. If that's the case, you can do:
SERVERS=(blah1.example.com blah2.example.com blah3.example.com blah4.example.com)
for i in $(seq 0 3)
do
echo ${SERVERS[$i]}
done
But if you just want to loop through the names and run an SSH command (ie if having an array won't provide useful functionality), the first method is more straightforward.
Your remote server probably calls a different shell when executing commands. Try to add bash -c to your arguments:
ssh user#server bash -c "<your commands>"
Or:
ssh user#server bash < yourscript.sh ## None in yourscript.sh must read input though.
An opening parenthesis starts a subshell, which is not a correct thing to have on the right side of an equals sign. It expects a string expression, not a command.
Quotation marks are used to keep a string expression together.