Passing a variable inside quotation marks to a command in bash

Question

Some context :

I'm attempting to run a command as part of a bash script to poll for system/device data.

# Recommended usage in the command line, contains single and double quotes
wbemcli ein 'http://localhost:5988/root/cimv2:some_class'
wbemcli gi 'http://localhost:5988/root/cimv2:some_class.DeviceID="Some Device ID"'

# I can get away with just 1 level of quotation marks
wbemcli ein http://localhost:5988/root/cimv2:some_class
wbemcli gi http://localhost:5988/root/cimv2:some_class.DeviceID="Some Device ID"
wbemcli gi http://localhost:5988/root/cimv2:some_class.DeviceID='Some Device ID'

So this is working ...

    #!/bin/sh

    C_PATH=http://localhost:5988/root/cimv2
    CLASS=some_class
    ID="Some Device ID"

    set -x
    wbemcli ein $C_PATH:$CLASS

Unfortunately, it falls apart when I attempt to integrate the quotation marks into the command. The code executed in the shell is unexpected to me.

    # Code
    wbemcli gi $C_PATH:$CLASS.DeviceID=\"$ID\"

    output $ ./myscript
    + wbemcli gi 'http://localhost:5988/root/cimv2:some_class.DeviceID="Some' Device 'ID"'

    # I was expecting this ...
    output $ ./myscript
    + wbemcli gi http://localhost:5988/root/cimv2:some_class.DeviceID="Some Device ID"

Bash is adding quotation marks in places I didn't expect. It's even enclosing the entire URL portion in single quotation marks. What's going on ?

Ansgar Wiechers · Accepted Answer · 2013-08-12 11:27:07Z

1

Try like this:

wbemcli gi -nl "$C_PATH:$CLASS.DeviceID=\"$ID\""

or like this:

wbemcli gi -nl "$C_PATH:$CLASS.DeviceID='$ID'"

answered Aug 12, 2013 at 11:27

Ansgar Wiechers

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6 Comments

peonicles Over a year ago

1st one gives + wbemcli gi -nl 'C_PATH:some_class.DeviceID="Some Device ID"' and 2nd one gives + wbemcli gi -nl 'C_PATH:some_class.DeviceID='\''Some Device ID'\'''

Jonathan Leffler Over a year ago

@peonicles: Both the traces are OK — the wbemcli command gets to see either single quotes or double quotes around the 'Some Device ID' and sees the whole string as a single argument even though there are spaces in 'Some Device ID'. bash does echo things differently under set -x from other shells; its output is typically unambiguous where other shells' output is ambiguous.

peonicles Over a year ago

ahh ok, I had a really dumb syntax error (omitted the $ in $C_PATH). #1 is working perfectly, thanks guys! #2 is still adding the weird '\' though.

Ansgar Wiechers Over a year ago

That's just how bash displays the string when you have set -x enabled. It's the string C_PATH:some_class.DeviceID=, followed by a literal single quote \', the string Some Device ID, another literal single quote \' and the empty string ''. You get this weird-looking representation, because nested single quotes can't be escaped in single-quoted strings.

peonicles Over a year ago

I've substituted in actual values into the variables, and #1 is working nicely. #2 seems to give me a usable string when I echo, but for some reason wbemcli is giving me errors. Your answer should work for other similar situations though.

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