Purpose of "read" and "$END$" in ksh ?


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Top Forums Shell Programming and Scripting Purpose of "read" and "$END$" in ksh ?
# 1  
Purpose of "read" and "$END$" in ksh ?

Hi,

Could anyone please shed some light on the following script lines and what is it doing as it was written by an ex-administrator?

cat $AMS/version|read a b verno d
DBVer=$(/usr/bin/printf "%7s" $verno)


I checked that the cat $AMS/version command returns following output:

Application Release 12.2L01 as of Fri Nov 2 22:11:46 EDT 2007

But when it is being piped through read in the above lines, nothing is available in DBVer parameter when I output using echo $DBVer. Smilie

Also what is the purpose of $END$ as in the following code:

$AMS/bin/procmon testdb << $END$

Thanks
# 2  
read takes one line, unless you muck with env I suppose, and puts the first field in the first variable and so on with the rest in the last variable. Apparently the version is the 3rd field of the first line. The cat is lazy, read <file is cheaper than a fork, pipe, exec of cat.

<< is a converter of script lines to stdin, and stops on a line with the following token only. The script lines are expanded for variables and such, so I prefer echo '...'|, where single quotes keep things literal. << copies the processed lines to a temp file, so it is the cost of a temp file create versus a pipe, echo being a builtin.

Last edited by DGPickett; 07-01-2011 at 12:59 PM..
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# 3  
Thanks for the reply.

1) But why it wouldn't return anything in DBVer parameter as that is empty after running those lines ?

2) So how this token $END$ is generated ? What key sequence would do that?

Regards,
# 4  
"echo 1 2| read a b c" means a=1, b=2, c=, garbage in is garbage out.

It is just a string, a token made up by the author. I use <<!, if I use it at all, as it takes less space and works fine. Must be exactly and only on a line by itself. Nice to keep lists one item a line for easy maintenance and viewing, not "a b ccc ddd ee ff ggg". You deserve neat, clean, clear code.
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# 5  
Quote:
Also what is the purpose of $END$ as in the following code:
$AMS/bin/procmon testdb << $END$
This is a Shell "Here" document. All the ensuing lines up to but not including the string $END$ are presented on the input read channel of the program $AMS/bin/procmon .
There should be a corresponding $END$ in column 1 a number of lines later in the script.
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# 6  
Yeah, interview answer, here document. The token can be anything, 'EOF' is very popular.

The $ are a real bad token character choices, normally being used in shell and environmental variable retreivals. The make it look magic, ooooh, ooooh, Levitosa, accio broom! Smilie
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# 7  
Ok so if I try to test the example you have sent:
--------------------
#!/bin/ksh
echo 1 2 | read a b c
echo $b
--------------------

$b still has blank value instead of 2 !
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