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murffatksig

Member

From: Atl

Registered: 2004-05-17

Posts: 362

Simple programming question

I'm examining some PKGBUILD's to hopefully learn to make my own.  And I've seen this line

make || return 1

.  I understand that's where the code is compiled according to the makefile, but why the

|| return 1

I know  return 1 just returns success, but why would you want that?  and what does the || do?

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brisbin33

Member

From: boston, ma

Registered: 2008-07-24

Posts: 1,799

Website

Re: Simple programming question

&& and || check a previous command for successful completion or failure respectively (more exactly, a zero or nonzero exit status)

i.e.

cd $HOME && rm ./*

will only do the rm if the cd completes successfully

or

make || return 1

will only return (with a 1 exit status) if the make command fails.  this is a good way to break out of a script/function/loop if something fails

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Xyne

Forum Fellow

Registered: 2008-08-03

Posts: 6,965

Website

Re: Simple programming question

If the build function returns 1 then it is considered an error (most applications return 0 upon success and something else when there is an error).

"make || return 1" could be read as "Try to compile the code. If there is an error, exit the build function and report an error, otherwise continue.".

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moljac024

Member

From: Serbia

Registered: 2008-01-29

Posts: 2,676

Re: Simple programming question

You can try to understand it this way;

&& looks like the logical AND
|| looks like the logical OR

So, in that case - either do command1 with success OR do command2.

Last edited by moljac024 (2009-06-09 00:17:01)

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Peasantoid

Member

Registered: 2009-04-26

Posts: 928

Website

Re: Simple programming question

In the land of shell scripting, 0 is success and anything else is failure.

Also, you might find this informative: http://en.wikipedia.org/wiki/Short-circuit_evaluation

Last edited by Peasantoid (2009-06-09 00:20:37)