VERY confused about forking of child process - UNIX for Advanced & Expert Users

JamesByars · #1 02-21-2008

hi,

I thought that when a child shell is forked, it will inherit all the variables of the parent

now in my .cshrc I have

Code:

setenv X x

then I do at command line

Code:

setenv X y

and X is now y. So far so good!

I then have a very simple script, y.csh

Code:

#!/usr/bin/csh

echo X

Now when I do

Code:

%: y.csh

x gets printed. Why? I thought the child will inherit all the variables of its parent. So it should inherit X as y, yes?

thanks.

fpmurphy · #2 02-21-2008

Works as expected for me

Code:

%setenv X x
%echo $X
x
%setenv X y
%echo $X
y
%cat t
#!/usr/bin/csh

echo $X
%./t
y
%

JamesByars · #3 02-22-2008

no, I think you missed the bit that my .cshrc also sets X (to x)

thanks

manikantants · #4 02-22-2008

Quote:

Originally Posted by JamesByars

hi,

I thought that when a child shell is forked, it will inherit all the variables of the parent

now in my .cshrc I have

Code:

setenv X x

then I do at command line

Code:

setenv X y

and X is now y. So far so good!

I then have a very simple script, y.csh

Code:

#!/usr/bin/csh

echo X

Now when I do

Code:

%: y.csh

x gets printed. Why? I thought the child will inherit all the variables of its parent. So it should inherit X as y, yes?

thanks.

There is nothing strange in the output.
going through your "y.sh", you gave "echo X" - which will print "X"
if you want to print value in variable X, you should have given "echo $X"

jim mcnamara · #5 02-22-2008

Unless it is a requirement, consider using a shell that does not have the problems csh has.

Here is an article, feel free to disagree:
into the wibble [csh is bad]

JamesByars · #6 02-22-2008

sorry, I DO have echo $X.

Code:

#!/usr/bin/csh

echo $X

To sum up, this is what is happening:

1) .cshrc sets X to x
2) I setenv X y in my shell
3) I then do y.csh

Now I know .cshrc will be called everytime a csh script is called. And obviously in this script we;re setting X to x. But I also thought that the child shell will inherit all the parents variables. So I would have expected it to inherit X = y, and for this to overrride whatever is happening in the .cshrc!

thanks.

denn · #7 02-22-2008

Please do a "man csh"
-f Suppress execution of the .cshrc file

change your script from:

Code:

#!/usr/bin/csh
echo $X

to:

Code:

#!/usr/bin/csh -f
echo $X

More UNIX and Linux Forum Topics You Might Find Helpful
Thread	Thread Starter	Forum	Replies	Last Post
Can a child process return a specific value to a parent process ?	Ametis1970	High Level Programming	8	04-09-2008 08:22 PM
Testing the forking process.	Vitamin254	UNIX for Dummies Questions & Answers	0	02-22-2008 08:12 PM
forking process.	kymthasneem	High Level Programming	2	06-23-2007 10:00 AM
forking a new process	themezzaman	High Level Programming	4	06-20-2006 01:13 AM
KDM child process	larryase	UNIX for Dummies Questions & Answers	6	01-24-2005 02:41 PM

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode