trap in shell programming
xinyou yan
yxy.716 at gmail.com
Mon Mar 7 08:01:24 UTC 2011
thank you !
As you write . It works .
I thought it was captured by shell. In fact the error in cods.
I am just a student .
Someone told me some skills are import . However , I study it and
find I can't use it right now .
That lead careless .
May be we need to find interest in programming .
2011/3/7 Cameron Simpson <cs at zip.com.au>:
> On 07Mar2011 10:17, xinyou yan <yxy.716 at gmail.com> wrote:
> | I want to know when i use
> |
> | trap 'rm -f /tmp/my_tmp_file_$$' INT
> |
> | why shell itself capture the single and she shellscript exit.
>
> But it doesn't!
>
> The shell captures the signal, runs the rm command, and proceeds.
>
> | Here is the code from << Beginning Programming>>
> | #!/bin/sh
> | trap 'rm -f /tmp/my_tmp_file_$$' INT
> | echo creating file /tmp/my_tmp_file_$$
> | date > /tmp/my_tmp_file_$$
> |
> | echo "Press interrupt (Ctrl-C) to interrupt...."
> | while [ -f /tmp/my_tmp_file_$$ ]; do
> | echo File exists
> | sleep 1
> | done
> | echo The file no longer exists
>
> When I run this script, this all works just fine.
>
> | trap INT
>
> However, _this_ line above is incorrect.
> "trap" requires a shell command to run, even if it is empty.
> For example:
>
> trap 'echo INT received' INT
>
> >From "man sh":
>
> trap [-lp] [[arg] sigspec ...]
> The command arg is to be read and executed when the shell
> receives signal(s) sigspec. [...snip...] If arg is the null
> string the signal specified by each sigspec is ignored by the shell
> and by the commands it invokes. [...snip...]
>
> When I run the script it aborts at that line.
>
> Try changing that line to:
>
> trap 'echo INT received' INT
>
> and rerunning your script.
>
> Cheers,
> --
> Cameron Simpson <cs at zip.com.au> DoD#743
> http://www.cskk.ezoshosting.com/cs/
>
> More computing sins have been committed in the name of performance,
> without necessariliy achieving it, than for all other reasons
> combined. - Wulf
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