[SOLVED] Using trap in bash script

sree_ec · 11-21-2010, 11:48 AM

Code:

#!/bin/sh
onexit()
{

echo "Error At line - $1"


}
trap 'onexit ${LINENO}' 127

Why this code gives me error

Quote:

trap: 127: bad trap

I tried

Code:

trap 'onexit ${LINENO}' ERR

as well. It gives me same error

What I want to do is to make the onexit function to handle any generic error that comes during script execution. I am not thinking about using 'set -e' since it will cause a quick exit.
I did 127, because I wanted my script to handle atleast the command not found error.
I am not thinking about handling any interrupt or any other signal at the moment.

pupok · 11-21-2010, 05:31 PM

Try it this way

Code:

#!/bin/sh
onexit()
{
echo "Error At line - $1"
}
trap "{ onexit \${LINENO} ; }" ERR

badcommand1
ls -d /
badcommand2

ntubski · 11-21-2010, 07:47 PM

Trap deals with signals not exit status.

Code:

~$ help trap
trap: trap [-lp] [[arg] signal_spec ...]
    Trap signals and other events.
...
    If a SIGNAL_SPEC is EXIT (0) ARG is executed on exit from the shell.  If
    a SIGNAL_SPEC is DEBUG, ARG is executed before every simple command.
    
...    
    Options:
      -l	print a list of signal names and their corresponding numbers
      -p	display the trap commands associated with each SIGNAL_SPEC
    
    Each SIGNAL_SPEC is either a signal name in <signal.h> or a signal number.
...
~$ trap -l
 1) SIGHUP	 2) SIGINT	 3) SIGQUIT	 4) SIGILL	 5) SIGTRAP
 6) SIGABRT	 7) SIGBUS	 8) SIGFPE	 9) SIGKILL	10) SIGUSR1
11) SIGSEGV	12) SIGUSR2	13) SIGPIPE	14) SIGALRM	15) SIGTERM
16) SIGSTKFLT	17) SIGCHLD	18) SIGCONT	19) SIGSTOP	20) SIGTSTP
21) SIGTTIN	22) SIGTTOU	23) SIGURG	24) SIGXCPU	25) SIGXFSZ
26) SIGVTALRM	27) SIGPROF	28) SIGWINCH	29) SIGIO	30) SIGPWR
31) SIGSYS	34) SIGRTMIN	35) SIGRTMIN+1	36) SIGRTMIN+2	37) SIGRTMIN+3
38) SIGRTMIN+4	39) SIGRTMIN+5	40) SIGRTMIN+6	41) SIGRTMIN+7	42) SIGRTMIN+8
43) SIGRTMIN+9	44) SIGRTMIN+10	45) SIGRTMIN+11	46) SIGRTMIN+12	47) SIGRTMIN+13
48) SIGRTMIN+14	49) SIGRTMIN+15	50) SIGRTMAX-14	51) SIGRTMAX-13	52) SIGRTMAX-12
53) SIGRTMAX-11	54) SIGRTMAX-10	55) SIGRTMAX-9	56) SIGRTMAX-8	57) SIGRTMAX-7
58) SIGRTMAX-6	59) SIGRTMAX-5	60) SIGRTMAX-4	61) SIGRTMAX-3	62) SIGRTMAX-2
63) SIGRTMAX-1	64) SIGRTMAX

ERR isn't one of the signals.

sree_ec · 11-21-2010, 11:05 PM

Quote:

Originally Posted by pupok

Try it this way

Code:

#!/bin/sh
onexit()
{
echo "Error At line - $1"
}
trap "{ onexit \${LINENO} ; }" ERR

badcommand1
ls -d /
badcommand2

Thanks mate. It works in RHEL..
But even my old code works when I tested it in RHEL. I first tested it on ubuntu ,but my code was not working.
I will test yours in ubuntu as well and post the result here .

catkin · 11-22-2010, 04:56 AM

FYI:

Code:

c@CW8:~$ trap -l | grep ERR
c@CW8:~$ trap 'foo \$LINENO' ERR
[no output]
c@CW8:~$ echo $?
0
c@CW8:~$ bash --version
GNU bash, version 4.1.7(2)-release (x86_64-slackware-linux-gnu)
[snip]

sree_ec · 11-22-2010, 11:20 AM

Quote:

Originally Posted by catkin

FYI:

Code:

c@CW8:~$ trap -l | grep ERR
c@CW8:~$ trap 'foo \$LINENO' ERR
[no output]
c@CW8:~$ echo $?
0
c@CW8:~$ bash --version
GNU bash, version 4.1.7(2)-release (x86_64-slackware-linux-gnu)
[snip]

Which means this works right?
Why this is not working in ubuntu??

I have used the above ccode as well which worked for me in RHEL.. That is also not working well in ubuntu.. It is showing bad trap....

sree_ec · 11-22-2010, 11:22 AM

Quote:

Originally Posted by sree_ec

Which means this works right?
Why this is not working in ubuntu??

I have used the above ccode as well which worked for me in RHEL.. That is also not working well in ubuntu.. It is showing bad trap....

Quote:

sreejith@sreejith-Inspiron-N4010:~/work/shellscript$ trap 'foo \$LINENO' ERR
sreejith@sreejith-Inspiron-N4010:~/work/shellscript$ echo $?
0
sreejith@sreejith-Inspiron-N4010:~/work/shellscript$ bash --version
GNU bash, version 4.1.5(1)-release (i686-pc-linux-gnu)
Copyright (C) 2009 Free Software Foundation, Inc.

Why in shell script alone, it is showing bad trap???

catkin · 11-22-2010, 02:40 PM

Quote:

Originally Posted by sree_ec

Which means this works right?

Yes:

Code:

c@CW8:~$ trap foo ERR
c@CW8:~$ function foo {
> echo foo running
> }
c@CW8:~$ jfhdsfh
bash: jfhdsfh: command not found
foo running

Which bash version do you have? bash --version will tell.

ntubski · 11-22-2010, 03:14 PM

Quote:

Originally Posted by sree_ec

Why in shell script alone, it is showing bad trap???

Probably in Ubuntu /bin/sh links to dash which doesn't support the pseudo-signal ERR, use #!/bin/bash instead.

@catkin: interesting, apparently the help text is missing some info. You've got an extra level of escaping though:

Code:

~$ foo() { echo lineo: $1; }
~$ trap 'foo \$LINENO' ERR
~$ false
lineo: $LINENO
~$ trap 'foo $LINENO' ERR
~$ false
lineo: 6
~$ trap "foo \$LINENO" ERR
~$ false
lineo: 8

Code:

$ man bash
...
       trap [-lp] [[arg] sigspec ...]
              If  a  sigspec is EXIT (0) the command arg is executed on exit from
              the shell.  If a sigspec is DEBUG,  the  command  arg  is  executed
              before every simple command, for command, case command, select com‐
              mand, every arithmetic for command, and before  the  first  command
              executes  in  a shell function (see SHELL GRAMMAR above).  Refer to
              the description of the extdebug option to  the  shopt  builtin  for
              details  of  its effect on the DEBUG trap.  If a sigspec is RETURN,
              the command arg is executed each time a shell function or a  script
              executed with the . or source builtins finishes executing.

              If  a sigspec is ERR, the command arg is executed whenever a simple
              command has a non-zero exit status, subject to the following condi‐
              tions.   The ERR trap is not executed if the failed command is part
              of the command list immediately following a while or until keyword,
              part  of the test in an if statement, part of a command executed in
              a && or ⎪⎪ list, or if the command's return value is being inverted
              via !.  These are the same conditions obeyed by the errexit option.

catkin · 11-22-2010, 08:51 PM

Quote:

Originally Posted by ntubski

@catkin: interesting, apparently the help text is missing some info. You've got an extra level of escaping though

Oops! Thank you for pointing it out

sree_ec · 11-23-2010, 09:28 AM

Quote:

Originally Posted by ntubski

Probably in Ubuntu /bin/sh links to dash which doesn't support the pseudo-signal ERR, use #!/bin/bash instead.

@catkin: interesting, apparently the help text is missing some info. You've got an extra level of escaping though:

Code:

~$ foo() { echo lineo: $1; }
~$ trap 'foo \$LINENO' ERR
~$ false
lineo: $LINENO
~$ trap 'foo $LINENO' ERR
~$ false
lineo: 6
~$ trap "foo \$LINENO" ERR
~$ false
lineo: 8

Code:

$ man bash
...
       trap [-lp] [[arg] sigspec ...]
              If  a  sigspec is EXIT (0) the command arg is executed on exit from
              the shell.  If a sigspec is DEBUG,  the  command  arg  is  executed
              before every simple command, for command, case command, select com‐
              mand, every arithmetic for command, and before  the  first  command
              executes  in  a shell function (see SHELL GRAMMAR above).  Refer to
              the description of the extdebug option to  the  shopt  builtin  for
              details  of  its effect on the DEBUG trap.  If a sigspec is RETURN,
              the command arg is executed each time a shell function or a  script
              executed with the . or source builtins finishes executing.

              If  a sigspec is ERR, the command arg is executed whenever a simple
              command has a non-zero exit status, subject to the following condi‐
              tions.   The ERR trap is not executed if the failed command is part
              of the command list immediately following a while or until keyword,
              part  of the test in an if statement, part of a command executed in
              a && or ⎪⎪ list, or if the command's return value is being inverted
              via !.  These are the same conditions obeyed by the errexit option.

You are spot on..
It is pointing to dash.. In dash I get this error!!!

leaveinriver · 03-26-2012, 07:26 AM

Quote:

Originally Posted by ntubski

Probably in Ubuntu /bin/sh links to dash which doesn't support the pseudo-signal ERR, use #!/bin/bash instead.

@catkin: interesting, apparently the help text is missing some info. You've got an extra level of escaping though:

Code:

~$ foo() { echo lineo: $1; }
~$ trap 'foo \$LINENO' ERR
~$ false
lineo: $LINENO
~$ trap 'foo $LINENO' ERR
~$ false
lineo: 6
~$ trap "foo \$LINENO" ERR
~$ false
lineo: 8

Code:

$ man bash
...
       trap [-lp] [[arg] sigspec ...]
              If  a  sigspec is EXIT (0) the command arg is executed on exit from
              the shell.  If a sigspec is DEBUG,  the  command  arg  is  executed
              before every simple command, for command, case command, select com‐
              mand, every arithmetic for command, and before  the  first  command
              executes  in  a shell function (see SHELL GRAMMAR above).  Refer to
              the description of the extdebug option to  the  shopt  builtin  for
              details  of  its effect on the DEBUG trap.  If a sigspec is RETURN,
              the command arg is executed each time a shell function or a  script
              executed with the . or source builtins finishes executing.

              If  a sigspec is ERR, the command arg is executed whenever a simple
              command has a non-zero exit status, subject to the following condi‐
              tions.   The ERR trap is not executed if the failed command is part
              of the command list immediately following a while or until keyword,
              part  of the test in an if statement, part of a command executed in
              a && or ⎪⎪ list, or if the command's return value is being inverted
              via !.  These are the same conditions obeyed by the errexit option.

I had the same problem, change the first line to "#!/bin/bash" in the script may solve this issue.
But if my script's first line is "#!/bin/sh", I execute "echo $SHELL", I also get the result "/bin/bash". So I don't know where is different between "#!/bin/sh" to "#!/bin/bash".

catkin · 03-26-2012, 08:34 AM

Please start a new thread for your question

ntubski · 03-28-2012, 10:48 PM

Quote:

Originally Posted by leaveinriver

But if my script's first line is "#!/bin/sh", I execute "echo $SHELL", I also get the result "/bin/bash".

$SHELL doesn't tell you the current shell, it tells what shell the current user will login to.

Code:

% echo $SHELL
/usr/bin/zsh
% bash
~/tmp$ echo $SHELL
/usr/bin/zsh
~/tmp$ exit
exit
% dash
$ echo $SHELL
/usr/bin/zsh