Signal handling help

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May 23rd, 2012, 04:32 PM

Squ3lch

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Signal handling help

I have been working on a Linux programming book and came to an example on signal handling that gave me a hangup. I checked to make sure I copied it alright so I don't believe that's it. Here's the example:

Code:

#!/bin/sh

trap 'rm -f /temp/my_tmp_file_$$' INT
echo creating file /tmp/my_temp_file_$$
date > /tmp/my_temp_file_$$
echo "Press interrupt (CTRL-C) to interrup ...."
while [ -f /tmp/my_tmp_file_$$ ]; do
        echo File Exists
        sleep 1
done
echo The file no longer exists

[highlight]trap INT
echo creating file /tmp/my_tmp_file_$$
date > /tmp/my_temp_file_$$

echo "press interrupt to interrupt ...."
while [ -f /tmp/my_temp_file_$$ ]; do
        echo File Exists
        sleep 1
done

echo we never get here
exit 0

Which gives me the output:

Code:

creating file /tmp/my_temp_file_18058
Press interrupt (CTRL-C) to interrup ....
The file no longer exists
trap: usage: trap [-lp] [[arg] signal_spec ...]

I'm guessing it's in the trap statement syntax. Perhaps outdated usage?
Thanks for any help.

May 23rd, 2012, 05:33 PM

SimonJM

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I suspect it is because the SIGINT trap having been 'fired' once is no longer active and hence cannot be reset by the 'simple' use of trap INT.

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May 23rd, 2012, 05:59 PM

Squ3lch

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Quote:

Originally Posted by SimonJM

I suspect it is because the SIGINT trap having been 'fired' once is no longer active and hence cannot be reset by the 'simple' use of trap INT.

Wouldn't that mean I would have to press ctrl-c at least once? The output I gave happens immediately after running and then exits. It seems like it only executes the first section of code before exiting on its own. Perhaps the trouble is in creating the file, exiting the loop before the interrupt?

May 23rd, 2012, 06:11 PM

Squ3lch

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Sorry guys. Problems was just a few mixups between tmp and temp. Yet another example of thoroughly checking the code. After that the file does run as expected.

Signal handling help

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