12-09-2006
trap command in Unix
Could anybody tell me what the trap command does and how it performs the action it does. I had read the trap manual page but it is too concise that nothing is clear about it. Please tell how it works.
10 More Discussions You Might Find Interesting
1. Shell Programming and Scripting
I'm using the trap command to capture any signals received whilst my script is running.
How's the best way of writing the signal and any other error messages to a file/error log' without having to type '2>$1' on the command line after the script name?
Cheers (3 Replies)
Discussion started by: dbrundrett
3 Replies
2. UNIX for Dummies Questions & Answers
i have the following script that displays the current time until the user presses CTR + c.... but it does not work properly....
Something is not right with the trap command...
Help plz... :confused:
# script to continuously display current time.
# if script is terminated trap signal... (3 Replies)
Discussion started by: onlyc
3 Replies
3. UNIX for Dummies Questions & Answers
Dear All
could you please explain me what does the trap command do and how I can write a program which can work as a trap command(in C Language). (1 Reply)
Discussion started by: mobile01
1 Replies
4. Shell Programming and Scripting
Hi,
I would like to know the use of TRAP command. I am very new to the UNIX environment. I have just started learning the basic. So please teach me in a very simple way to understand.
Also i would like to know the use of following command:
trap 'dialog --msgbox "Script Aborted1" 6 50 ;... (2 Replies)
Discussion started by: Deepakh
2 Replies
5. Shell Programming and Scripting
Hi folks,
I have tried to add some trap detection in the below script....this script is used to monitor database activities...in a rather awkward way :rolleyes:....
The idea behind adding trap is that....this script creates lots of temporary files in the running folder to store the count... (1 Reply)
Discussion started by: frozensmilz
1 Replies
6. Shell Programming and Scripting
Hi
I am using "trap" command in my script to prevent the user from running Ctrl-C during the its execution. My script creates number of children processes which in turn create some children processes as well during the execution.
When user / tester tries to run Ctrl-C, the parent process is... (1 Reply)
Discussion started by: aoussenko
1 Replies
7. UNIX for Advanced & Expert Users
Hello experts!
I need to know the use of trap command please
In one of our program we have trap "rm -f temp1 ; exit 1" 1 2 15 0
and program always exit with 1
there is a rm -f temp1 as well at the end of the program
as
rm -f temp1
exit 0
when I test a probram with set... (4 Replies)
Discussion started by: ramshree01
4 Replies
8. UNIX for Dummies Questions & Answers
I'm learning about the trap command from my bash book. I tried out the little script they gave:
trap "echo 'You hit control-C!' " INT
while true; do
sleep 60
done
But when I type control-c, the script just stops and the message is not displayed. I checked stty all and saw that control-c... (11 Replies)
Discussion started by: Straitsfan
11 Replies
9. Shell Programming and Scripting
dear all;
I can't under stand what does "trap" command do:
for example see below:
trap "echo; echo no interrupts >&2; sleep 3" 2 3 15
Plz , can any body explain the action of this command?
BR (3 Replies)
Discussion started by: ahmad.diab
3 Replies
10. Homework & Coursework Questions
Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!
1. The problem statement, all variables and given/known data:
That is the last reply I received from my instructor, and I'm looking for some alternatives.
When using... (2 Replies)
Discussion started by: newuser45
2 Replies
trap(1) User Commands trap(1)
NAME
trap, onintr - shell built-in functions to respond to (hardware) signals
SYNOPSIS
sh
trap [ argument n [n2...]]
csh
onintr [-| label]
ksh
*trap [ arg sig [ sig2...]]
DESCRIPTION
sh
The trap command argument is to be read and executed when the shell receives numeric or symbolic signal(s) (n). (Note: argument is scanned
once when the trap is set and once when the trap is taken.) Trap commands are executed in order of signal number or corresponding symbolic
names. Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective. An attempt to trap on signal 11
(memory fault) produces an error. If argument is absent all trap(s) n are reset to their original values. If argument is the null string
this signal is ignored by the shell and by the commands it invokes. If n is 0 the command argument is executed on exit from the shell. The
trap command with no arguments prints a list of commands associated with each signal number.
csh
onintr controls the action of the shell on interrupts. With no arguments, onintr restores the default action of the shell on interrupts.
(The shell terminates shell scripts and returns to the terminal command input level). With the - argument, the shell ignores all inter-
rupts. With a label argument, the shell executes a goto label when an interrupt is received or a child process terminates because it was
interrupted.
ksh
trap uses arg as a command to be read and executed when the shell receives signal(s) sig. (Note that arg is scanned once when the trap is
set and once when the trap is taken.) Each sig can be given as a number or as the name of the signal. trap commands are executed in order
of signal number. Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective. If arg is omitted
or is -, then the trap(s) for each sig are reset to their original values. If arg is the null (the empty string, e.g., "" ) string then
this signal is ignored by the shell and by the commands it invokes. If sig is ERR then arg will be executed whenever a command has a non-
zero exit status. If sig is DEBUG then arg will be executed after each command. If sig is 0 or EXIT for a trap set outside any function
then the command arg is executed on exit from the shell. The trap command with no arguments prints a list of commands associated with each
signal number.
On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:
1. Variable assignment lists preceding the command remain in effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari-
able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not
performed.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO
csh(1), exit(1), ksh(1), sh(1), attributes(5)
SunOS 5.10 23 Oct 1994 trap(1)