Question

This is my first post here, so please bear with me…

I have discovered the amazing powers of .ssh/config after having fully configured my .bash_aliases file, and as I’m pretty lame with programming, I was looking for a nice way to parse the connection details from the bash_aliases file into the ~/.ssh/config file.

So, going into details, my bash_aliases looks like this:

alias serverA='ssh -i ~/.ssh/serverA.key -o $SRVR_ALV user@serverAhostname'
alias serverB='ssh -i ~/.ssh/serverB.key -o $SRVR_ALV user@serverBhostname'
....

Where I have defined a variable for ServerAliveInterval in $SRVR_ALV.

My intention is to parse that entry into this and in the meantime get rid of that ugly variable

Host serverA
HostName serverAhostname
IdentityFile ~/.ssh/serverA.key

Host serverB
.....

What do you think is the best way to perform this? I was looking for a nice bash script, or perhaps using vi capabilities.
Thanks in advance!

Answer 1

How about some Perl?

perl -ne "/^alias (.*)='ssh -i (.*) -o (.*) (.*)\@(.*)'/ and 
    print qq{Host \$1\nHostName \$5\nIdentityFile \$2\n\n}" < \
 ~/.bash_aliases

If you like what you see, redirect it to append to >> ~/.ssh/config

[Update] – an explanation for the non-Perl user as to what’s going on:

perl -ne: -e means, ‘The next argument is the script to (e)xecute’.
-nmeans, '*run the given script once per line*' - so-necan sort-of
emulatesed`.

The perl code:

/^alias (.*)='ssh -i (.*) -o (.*) (.*)\@(.*)'/ and 
print qq{Host \$1\nHostName \$5\nIdentityFile \$2\n\n}

reads: for only the lines that match the regexp /^alias ../, print a string (qq{...} is that same as "..." in Perl), and the interpolated variables "\$1", "\$4" etc are the result of what was captured in the regexp.

perl -ne expects input, which comes from < ~/.bash_aliases.