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January
12, 2004 -
Subshells & Subshell Grouping - Part
II
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The
Korn shell automatically creates a
subshell to perform these operations:
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·
commands enclosed by parenthesis
· each section of a pipeline (minus the
last)
· background processes
· co-processes
· command substitution
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Enclosing
commands in parenthesis - ( command1;
command2; commandn; ) - produces a
different result than enclosing the same
commands in braces - { command1; command2;
commandn; }. The reason for this is
because commands inside of braces are
executed within the current session (a
subshell is not created).
Consider the following series of commands:
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[livefire@hawk] # pwd
/export/home/livefire
[livefire@hawk] # ( cd /tmp; pwd; )
/tmp
[livefire@hawk] # pwd
/export/home/livefire
[livefire@hawk] # { cd /tmp; pwd; }
/tmp
[livefire@hawk] # pwd
/tmp
[livefire@hawk] #
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As
you can see from the above output, when the
cd command is executed from within
parenthesis, the working directory of the
shell remains unchanged. The same is
obviously not true when braces are used.
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Learn
more...
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