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I try to pass sed via ssh command as [1] to ssh command, but it does not work. I do ssh to a host, like 'ssh ld3646'. In my console, I input 

ssh ld3646 'sed -i 's/USE_KERNEL_NFSD_NUMBER="4"/USE_KERNEL_NFSD_NUMBER="64"/g' /etc/sysconfig/nfs'

file /etc/sysconfig/nfs is not changed at all. It works when I do 'ssh ld3646' and type 

sed -i 's/USE_KERNEL_NFSD_NUMBER="4"/USE_KERNEL_NFSD_NUMBER="64"/g' /etc/sysconfig/nfs'

Can someone help on why doesn't it work?

user3659963
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  • Check this out: http://gt-dev.blogspot.com/2015/05/bash-ssh-how-to-invoke-command-remotely.html – g-t Apr 05 '16 at 12:03

2 Answers2

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Notice how you have two sets of single quotes? That doesn't work. Single quotes don't nest. Luckily, the outer set of quotes isn't necessary.

ssh ld3646 sed -i 's/USE_KERNEL_NFSD_NUMBER="4"/USE_KERNEL_NFSD_NUMBER="64"/g' /etc/sysconfig/nfs
John Kugelman
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You're experiencing quote confusion.

The quote immediately before the sed script EXITS the quoted string that begins with sed.

I provided some strategies for handling nested quotes in this answer, which might be enlightening. In your case, an easy strategy might be simply to change quotes:

ssh ld3646 "sed -i 's/USE_KERNEL_NFSD_NUMBER=\"4\"/USE_KERNEL_NFSD_NUMBER=\"64\"/g' /etc/sysconfig/nfs"

Note that the embedded double quotes are escaped, to avoid precisely this problem.

Another option for visual simplification might be to use variables:

sedscript='s/USE_KERNEL_NFSD_NUMBER="4"/USE_KERNEL_NFSD_NUMBER="64"/g'
ssh ld3646 "sed -i '$sedscript'"

This last one works because single quotes that are embedded in double-quoted strings do not block variable expansion.

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ghoti
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