How to use single quotes inside awk statement that is surrounded by single quotes?

Question

I'm having issues implementing this awk statement that I need for my script:

rsh fooDNS '
    ...

    BROADCAST_IP_ADDRESS=$(/usr/sbin/ifconfig $IF_NAME | grep broadcast |  awk '{print \$6}')
    ...
'

The issue here is that the statement above is contained within an rsh command surrounded by single quotations. Consequently, bash cannot interpret the single quotations around {print $6}, which is giving me a lot of problems. So far, I haven't been able to determine how to get around this issue.

Unrelated to the question, but the grep is not needed. `ifconfig ... | awk "/broadcast/{ print $6}"` — William Pursell, Jul 10 '12 at 10:41

Walter Mundt · Accepted Answer · 2012-07-09T23:58:11.960

You can't nest single quotes, but you can end the single quoted string, include an escaped single quote, and then re-enter the quotes. Try this:

rsh fooDNS '
    ...

    BROADCAST_IP_ADDRESS=$(/usr/sbin/ifconfig $IF_NAME | grep broadcast |  awk '\''{print $6}'\'')
    ...
'

Nonetheless, this kind of quoting madness gets ugly very quickly. If at all possible, I recommend using scp/rcp/ftp to copy a normal bash script over to the remote and then run that. Failing that, I think you can use a trick like this if you don't need to feed anything to the script's stdin:

cat script_file | rsh fooDNS bash

(Use rsh fooDNS /bin/sh if your script is plain-sh-compatible and the remote side doesn't have bash, of course.)

As yet another alternative, if your snippet is short you can use here docs:

rsh fooDNS sh <<'EOF'
    ...
    BROADCAST_IP_ADDRESS=$(/usr/sbin/ifconfig $IF_NAME | grep broadcast |  awk '{print $6}')
    ...
EOF

Thanks a bunch. I was stuck on this for hours. Incidentally, the above answer will only work if the backslash was removed from behind $6, but otherwise, this was really really helpful. Thanks. — Justin, Jul 10 '12 at 00:02

Jonathan Leffler · Answer 2 · 2012-07-10T01:39:19.417

Replace the embedded single quotes by the sequence '\'' each time. In theory, you can just do:

rsh fooDNS '
    ...
    BROADCAST_IP_ADDRESS=$(/usr/sbin/ifconfig $IF_NAME | grep broadcast |
    awk '\''{print $6}'\'')
    ...
'

The first ' ends the current single quoted string; the \' sequence adds a single quote; the final ' restarts a new (but contiguous) single-quoted string. So, this introduces no spaces or anything.

On the other hand, it is best to avoid needing to do that. It is vulnerable to causing problems when the string is reinterpreted. And this is doubly the case when dealing with remote shells.

score 1 · Answer 3 · answered Jul 10 '12 at 00:32

I usually use double quotes for deep nesting when doing it manually, or a mix of double and single quotes automatically.

If you do it manually, it's probably simpler to just escape your nested double quotes, apostrophes and dollar signs with backslashes, and avoid doing more than one or two levels deep.

Sometimes, instead of nesting the quotes manually, I'll use: http://stromberg.dnsalias.org/~strombrg/bashquote.html It can wrap up a string with double quotes automatically, exponentially. It uses a mix of double quotes and single quotes.

EG. from a minimal test of the code:

dstromberg@zareason-limbo6000a ~/src/home-svn/bashquote/trunk $ ./bashquote.py
unquoted: 'This is a test'
repetition 0: ''"'"'This is a test'"'"''
repetition 1: ''"'"''"'"'"'"'"'"'"'"'This is a test'"'"'"'"'"'"'"'"''"'"''
repetition 2: ''"'"''"'"'"'"'"'"'"'"''"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'This is a test'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"''"'"'"'"'"'"'"'"''"'"''
Final version: ''"'"''"'"'"'"'"'"'"'"''"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'This is a test'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"''"'"'"'"'"'"'"'"''"'"''
''"'"''"'"'"'"'"'"'"'"''"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'This is a test'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"'"''"'"'"'"'"'"'"'"''"'"''

That should be good for hopping through 3 ssh's and executing on the 4th.

One hopes one isn't driven to such levels of silliness. Still, if the tool gets it right, it looks useful. — sarnold, Jul 10 '12 at 00:52

score 1 · Answer 4 · answered Jul 10 '12 at 00:49

For AWK scripts I set a variable to the octal equivalent.

But in a case like yours, I would use double quotes and make sure to escape everything that might be interpreted by the shell such as the dollar sign as you have done.

And I wouldn't use rsh since it's insecure.

How to use single quotes inside awk statement that is surrounded by single quotes?

4 Answers4