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bashshellunixsshxargs

Using xargs to ssh to multiple hosts, receiving :Name or service not known

I am writing a shell script that will ssh to multiple hosts, and perform some operations on them.

my script, test.sh, looks as follows:

cat < $1 | xargs -e -d ' ' -I % ssh % grep "example" /opt/example/test.log

I run it via the following command

./test.sh prod_hosts.txt

and the contents of prod_hosts.txt:

hostname1 hostname2 hostname3 hostname4

I have verified there is no carraige return at the end of this file, yet I am getting the following error:

[ryan@hostname1 ~]$ ./test.sh prod_hosts.txt
ssh: hostname4
: Name or service not known
xargs: ssh: exited with status 255; aborting

It looks like it successfully ssh's into the 4 hosts but then has a blank entry that it is attempting to ssh with, hence the error.

Any idea what I'm missing here? Seems like I'm missing something obvious!

Solution

  • echo '1 2' | xargs -d ' ' -I % echo % produces:

    1
2
<blank line>

    whereas echo -n '1 2' | xargs -d ' ' -I % echo % returns:

    1
2

    i.e. xargs decides to generate one more output entry if the input string is ended by newline.

    Workarounds:

    1. Use newline delimited entries in hosts.txt and: <hosts.txt xargs -I % <ssh-command>
    2. If hosts.txt cannot be changed: < <(tr ' ' '\n' < hosts.txt) xargs -I % <ssh-command>