On 20Jun2017 10:19, bruce <badouglas@xxxxxxxxx> wrote:
Curious as to how to get the following to work remotely over SSH. The
cmd is used to remove redundant lines, while maintaining order in the
output file.
The following works if I insert it in the remote term.
cat /dog/aaa.dat | awk '!a[$0]++' > /dog/aaa.dat_tmp
However I'm unable to get the cmd to work via SSH from the local to
the remote. I've tried the following...
ssh crawl_user@67.205.11.111 cat /dog/aaa.dat | awk '!a[$0]++'
/dog/aaa.dat_tmp
This runs the cat remotely, fetching the remote file aaa.dat, then awks
locally, saving to the local file aaa.dat_tmp.
ssh crawl_user@67.205.11.111 ' cat /dog/aaa.dat | awk '!a[$0]++' >
/dog/aaa.dat_tmp '
This runs remotely, but the single quotes do not nest. You're opening some
quotes with the cat and closing just after the awk. The awk expression is not
quoted, not what you want.
ssh crawl_user@67.205.11.111 " cat /dog/aaa.dat | awk '!a[$0]++' >
/dog/aaa.dat_tmp "
This double quotes the whole thing: it all runs remotely, with single quotes
getting to the remote shell to quote the awk argument.
ssh crawl_user@67.205.11.111 ' cat /dog/aaa.dat | awk '\!a[$0]++' >
/dog/aaa.dat_tmp '
Like #2, but with a _local_ backslash to prevent the exclaimation mark being
used for local history expansion. So, incorrectly quoted.
ssh crawl_user@67.205.11.111 " cat /dog/aaa.dat | awk '\!a[$0]++' >
/dog/aaa.dat_tmp "
This doubnle quotes the remote command line as for #3, but in doubnle quotes
the slosh gets used up locally.
ssh crawl_user@67.205.11.111 ' cat /dog/aaa.dat | awk '"\!"a[$0]++' >
/dog/aaa.dat_tmp '
Kind of similar.
ssh crawl_user@67.205.11.111 " cat /dog/aaa.dat | awk '"\!"a[$0]++' >
/dog/aaa.dat_tmp "
This is in some ways like #2: you're (double) quoting from cat to awk; ah, I
see you're quoting the whole thing but exiting the quotes for the exclaimation
mark so that you can backslash it. That's actually pretty good.
In some cases, the cmd returns -- bash: !a[$0]++: event not found
Yes. Bash history expansion isn't really part of the shell command language, it
of more like an extra macro expansion that happens in the interactive command
line _before_ the shell's normal syntax is used.
One easy way to bypass the history expansion is to put your command in a
script; histpry expansion is an interactive thing, not active inside a script.
So a whole layer of annoyance is removed.
So your tasks are twofold: prevent bash wanting to do a history expansion when
it sees the exclaimation mark, and to get the command line intact to the far
end.
#7 above is the best of your choices, but you need the awk expression to get
into awk cleanly at the far end, so you need quotes at the far end.
I would be separating the construction of the remote command from the ssh call.
What you want remotely is what you pasted into the terminal:
cat /dog/aaa.dat | awk '!a[$0]++' >/dog/aaa.dat_tmp
It is generally best to use single quotes if you do not need to embed values in
the string, so cut #1 (not yet complete) would be:
shcmd='cat /dog/aaa.dat | awk '!a[$0]++' >/dog/aaa.dat_tmp'
However, you need the single quotes at the far end to prevent the remote shell
expanding the $0. I usually _keep_ the outer single quotes and exit the quote
just long enough to insert a literal single quote:
shcmd='cat /dog/aaa.dat | awk '\''!a[$0]++'\'' >/dog/aaa.dat_tmp'
That sequence '\'' is:
- ' exiting the first single quoted stretch
- \' putting in a literal single quote character
- ' entering single quotes again
Then I'd just use ssh:
ssh crawl_user@67.205.11.111 "$shcmd"
which keeps the logic much clearer.
Cheers,
Cameron Simpson <cs@xxxxxxxxxx>
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