Why does awk fail when part of ssh command?

Question

When I ssh into a server and run the command, it works:

$ssh -q postgres@XXXXX
Last login: Mon Mar 12 12:30:16 2018 from 10.101.XXX.X
[postgres@pgsdba203 ~]$ df -hP | grep pgsql | awk '{ if ($5 >= 70) print $0 }'
/dev/mapper/pgvg-pg_log  9.9G  7.2G  2.2G  77% /var/lib/pgsql/data/pg_log

But not when it's part of an ssh command parameter:

$ ssh -q postgres@XXXXX "df -hP | grep pgsql | awk '{ if ($5 >= 70) print $0 }'"
awk: { if ( >= 70) print -bash }
awk:        ^ syntax error

Since the awk command is in single quotes, I'd have expected the $5 to be preserved and passed directly to server XXXXX.

EDIT: the end goal is to make the server name into a variable and call ssh from within a bash for loop.

It's not in single quotes, though; the `'` are just characters in a double-quoted string, so `$5` is expanded before the string is even passed to the remote shell. — chepner, Mar 12 '18 at 17:01
BTW -- when you're asking a question similar to many others already in the knowledgebase, it's useful to call out the near-duplicates and show how you tried to apply the advice in each and how those attempts failed. (Though as some of the duplicates include the answer you're getting from Gilles, presumably some of those attempts *wouldn't* have failed in fact). — Charles Duffy, Mar 12 '18 at 17:26
@CharlesDuffy when typing in the subject, I looked at the existing questions that SO automatically suggested, but did not see anything relevant. — RonJohn, Mar 12 '18 at 17:30

Gilles Quénot · Answer 1 · 2018-03-12T16:47:44.990

1

What I would do :

ssh -q postgres@XXXXX <<'EOF'
df -hP | awk '/pgsql/ && $5 >= 70'
EOF

or in a for loop

for server in foo bar base; do
    ssh -q postgres@$server <<'EOF'
    df -hP | awk '/pgsql/ && $5 >= 70'
EOF
done

edited Mar 12 '18 at 16:47

answered Mar 12 '18 at 16:45

Gilles Quénot

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Thanks. Is that feasible within a for loop? – RonJohn Mar 12 '18 at 16:46
Check my edited post – Gilles Quénot Mar 12 '18 at 16:47
That doesn't seem to work either. – RonJohn Mar 12 '18 at 17:11
If you have error, report it – Gilles Quénot Mar 12 '18 at 17:14
I was doing that just as you made that comment... :) – RonJohn Mar 12 '18 at 17:15
Tested, work well – Gilles Quénot Mar 12 '18 at 17:17
Works well, *except* when you need to pass data over stdin and thus need to have it available for code. Which, granted, isn't the OP's immediate case here. – Charles Duffy Mar 12 '18 at 17:23
I still was using `-n`. Took that out and it works. – RonJohn Mar 12 '18 at 17:35

score 0 · Answer 2 · answered Mar 12 '18 at 17:21

As an easy-to-define pattern, which works even when you need to pipe stdin into your remote code: Define a shell function, and tell the shell itself to emit that function's literal text substituted into the remote command:

myfunc() { df -hP | grep pgsql | awk '{ if ($5 >= 70) print $0 }'; }
ssh -q postgres@XXXX "$(declare -f myfunc); myfunc"

Why does awk fail when part of ssh command?

2 Answers2