22.2.5 .
The semantics of `.' are rather peculiar to say the least. Here is
a simple script -- it just displays its positional parameters:
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#! /bin/sh
echo "$0" ${1+"$@"}
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Put this in a file, `foo'. Here is another simple script -- it
calls the first script. Put this in another file, `wrapper':
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#! /bin/sh
. ./foo
. ./foo bar baz
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Observe what happens when you run this from the command line:
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$ ./wrapper
./wrapper
./wrapper bar baz
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So `$0' is inherited from the calling script, and the positional
parameters are as passed to the command. Observe what happens when you
call the wrapper script with arguments:
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$ ./wrapper 1 2 3
./wrapper 1 2 3
./wrapper bar baz
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So the sourced script has access to the calling scripts positional
parameters, unless you override them in the `.' command.
This can cause no end of trouble if you are not expecting it, so you
must either be careful to omit all parameters to any `.' command,
or else don't reference the parameters inside the sourced script. If
you are reexecuting your script with a shell that understands functions,
the best use for the `.' command is to load libraries of functions
which can subsequently be used in the calling script.
Most importantly, don't forget that, if you call the exit
command in a script that you load with `.', it will cause the
calling script to exit too!
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