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Diff on Output of Remote Commands

Submitted by on January 25, 2016 – 1:47 pm

Let’s say you run the same command on two remote servers and you want to compare the output. Here’s a quick example:

diff <(ssh -qtT server01 "sudo su - root -c 'fdisk -l 2>/dev/null | grep ^Disk'") <(ssh -qtT server02 "sudo su - root -c 'fdisk -l 2>/dev/null | grep ^Disk'")

I suggest using “vimdiff” for a more easy-to-read layout:
yum -y install vim

vimdiff <(ssh -qtT server01 "sudo su - root -c 'fdisk -l 2>/dev/null | grep ^Disk'") <(ssh -qtT server02 "sudo su - root -c 'fdisk -l 2>/dev/null | grep ^Disk'")


Here’s another vimdiff example that ignores white spaces and uses a small script to auto-close in three seconds. The /tmp/vimscript looks like this:

:sleep 3

And the whole command is this:
vimdiff -c 'set diffopt+=iwhite' -s /tmp/vimscript <(ssh -qtT server2 "sudo su - root -c 'cat /etc/hosts'") <(ssh -qtT server1 "sudo su - root -c 'cat /etc/hosts'")

This may be useful if you need to do a quick visual comparison of multiple files. For example, find *.conf in /etc on server1 and compare them to equivalent files on server2:
for i in $(ssh -qtT server1 "sudo su - root -c 'find /etc -maxdepth 2 -type f -name "*\.conf"'" -mtime -7)
   vimdiff -c 'set diffopt+=iwhite' -s /tmp/vimscript <(ssh -qtT server1 "sudo su - root -c 'cat ${i}'") <(ssh -qtT server2 "sudo su - root -c 'cat ${i}'")


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