Saturday, October 9, 2010

unix subshell -- tips

http://www.ibm.com/developerworks/aix/tutorials/au-unixtips4/section5.html --

To run a group of commands in a subshell, enclose them in parentheses. You can use redirection to send input to the subshell's standard input or to send its *collective* output to a file or a pipeline.

Since the subshell environment is a duplicate of its parent, it inherits all of the variables of the parent. But the parent shell never sees any changes that are made in the subshell environment, and the subshell, in turn, never sees any changes that are made in the parent *after* the subshell is spawned.

To save return code of a command (among many) from a subshell,

echo $? > /tmp/hamper1390848908.$$
# other commands....
) > ${LOG_FILE} 2>&1
read GMI_RET_CODE </tmp/hamper1390848908.$$

Here's a simpler alternative

(
someJavaJob
javaStatus=$?
## any other command
[ $javaStatus -ne 0 ] && exit $javaStatus
) > ${LOG_FILE} 2>&1
subshellStatus=$?
echo $subshellStatus
exit $subshellStatus

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