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Why double quotation marks doesn't work in ksh function parameters passing?

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Top Forums Shell Programming and Scripting Why double quotation marks doesn't work in ksh function parameters passing?
# 1  
Old 06-13-2012
Why double quotation marks doesn't work in ksh function parameters passing?
I'm working on AIX 6, ksh shell. The parameters are some strings quotated by double quotation marks which from a file. They are quotated because there may be spaces in them.
Example:
Code:
 "015607" "10" "    " "A"

I want to pass these parameters to a shell function by writing the following command:
Code:
 parse $(cat para.txt)

But I didn't get 4 parameters as thought before, instead, there are 5 parameters!

OK, it's hard to say that problem clearly. the script is:

Code:
#!/bin/ksh
#################################
#
function parse {
    echo "[$1]"
    shift
    echo "[$1]"
    shift
    echo "[$1]"
    shift
    echo "[$1]"
    shift
    echo "[$1]"
    shift
}

echo write parameters directly
parse "009085" "              " "0405103025    " "0912" "0"
echo get parameters from file
parse $(cat para.txt)
####################################

The results is:
Code:
write parameters directly
[009085]
[              ]
[0405103025    ]
[0912]
[0]
get parameters from file
["009085"]
["]
["]
["0405103025]
["]

Why is that? What's the differents between these 2 ways of function call?
Is there a way to solve this problem?
Thanks for all information on it.
Last edited by Scott; 06-13-2012 at 04:16 AM.. Reason: Code tags
# 2  
Old 06-13-2012
Interesting...

As far as I can guess, when you directly pass parameters to the function using quotes to delimit them, the shell will consider the parameter list without the quotes but with the embedded white-spaces...

Code:
set -x

parse "009085" " " "0405103025 " "0912" "0"

+ parse 009085   0405103025  0912 0
[009085]
[ ]
[0405103025 ]
[0912]
[0]

But, when you get the argument list from a file using command substitution, the shell will do nothing more about it. It will use the current IFS value to decide the positional parameters.

Code:
parse "$(cat para.txt)"

+ cat para.txt
+ parse "009085" " " "0405103025 " "0912" "0"
["009085"]
["]
["]
["0405103025]
["]

# 3  
Old 06-13-2012
The issue is the order of events. We need to delay the Shell processing the parse line until after the cat has run.
Code:
#!/bin/ksh
#################################
#
function parse {
    echo "[$1]"
    shift
    echo "[$1]"
    shift
    echo "[$1]"
    shift
    echo "[$1]"
    shift
    echo "[$1]"
    shift
}

echo write parameters directly
parse "009085" "              " "0405103025    " "0912" "0"
echo get parameters from file
eval parse "$(cat para.txt)"

./scriptname
write parameters directly
[009085]
[              ]
[0405103025    ]
[0912]
[0]
get parameters from file
[009085]
[              ]
[0405103025    ]
[0912]
[0]


Contents of para.txt
"009085" "              " "0405103025    " "0912" "0"

Last edited by methyl; 06-13-2012 at 08:19 AM.. Reason: bad paste
# 4  
Old 06-14-2012
Thanks very much!
It's amazing...
I found there is so much knowledge need to learn.
Thanks a lot!
This User Gave Thanks to Shimmey For This Post:
methyl
# 5  
Old 06-14-2012
Though it is a solution to your problem, I don't recall ever putting an eval command in a production script.
There is always a better design like formatting your parameter file such that it is valid Shell syntax and can be executed in the current environment.
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