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assigning (numeric) command output to var tcsh

 
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# 1  
Old 08-28-2008
assigning (numeric) command output to var tcsh
Hello,

I'm trying to assign a numeric value that is returned from one of my programs to a variable in tcsh. I want to do:

@ r10 = './my_prog file 35'

where ./my_prog file 35 returns a decimal value, but this doesn't work. How do I achieve the desired result?

Janet
# 2  
Old 08-28-2008
Tools Child returning data to parent
What you are asking is for a child (called) process to return info to parent (master) program. The construct of unix does not allow for this as whatever is learned by the child does not have a way to naturally pass to parent; the reverse is ok, and is often accomplished with an EXPORT command.

Searching this forum will probably provide several creative solutions. Some are:
(a) return the value by way of the exit error parameter of the child back to the parent
(b) have the child write the data to a temporary file that the parent can then read
# 3  
Old 08-28-2008
Hi.

Keeping in mind that:
Quote:
The `@' command permits
numeric calculations to be performed and the result assigned to a vari-
able. Variable values are, however, always represented as (zero or
more) strings.

-- excerpt from man tcsh
We can use the following little script:
Code:
#!/usr/bin/env tcsh

@ result = 31416 * 2
echo $result

exit

As a source to set a variable in a larger script:
Code:
#!/usr/bin/env tcsh

# @(#) s1       Demonstrate script result capture.

echo
echo "(Versions displayed with local utility version)"
sh -c "version >/dev/null 2>&1" && version tcsh
echo

echo " Nonce script:"
cat -n t1

echo
echo " Results:"
set var1 = `./t1`
echo " var1 is $var1"

exit 0

Producing:
Code:
% ./s1

(Versions displayed with local utility version)
tcsh 6.13.00

 Nonce script:
     1  #!/usr/bin/env tcsh
     2
     3  @ result = 31416 * 2
     4  echo $result
     5
     6  exit

 Results:
 var1 is 62832

Note that the odd quotes (`) are backtics, not straight single quotes. See the man page for other details ... cheers, drl

(The usual advice advocating the use of Bourne family shells as opposed to csh family applies here.)
# 4  
Old 08-29-2008
If by "returned" you mean "written to standard output", then simply use backticks to capture the output of my_prog:
Code:
@ r10 = `./my_prog file 35`

Note that a tcsh @ variable must be assigned an integer value.
# 5  
Old 09-01-2008
Thanks folks...
Thanks for the really helpful posts.

A combination of writing only ints to standard output from my program and the use of backtics has cracked my problem.

Thanks for spending the time to explain & provide a solution too - much appreciated.
 
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