Effect of using eval to execute a command as opposed to writing it on the commandline
Code:
cmd='date | wc' or cmd="date | wc"
$cmd
If this script is executed, an error is generated. The reason written was that "The execution fails because the pipe is not expanded and is passed to date as an argument". What is meant by expansion of pipe. When we execute date | wc on the command line, it goes fine. then | is not treated as an argument. Why?
If I write
Code:
cmd='date | wc' or cmd="date | wc"
eval $cmd
It works. How?
I understand (hopefully) how eval works in 2 passes i.e. the command first gets evaluated and then executed.
Hi
i have the following code:
if(($line!=1) and (@field!='\$')){
print ( "\nTRY TO CONNECT TO DATABASE................\n");
my $dbh = DBI->connect($dsn, $user, $pass);
print ("CONNECTED TO DATABASE\n");
eval
... (1 Reply)
Hi All,
i have an issue regarding trap command.
i have specified trap function in the beginning of the script to catch some signals but in the later part of the script i want to remove the effect of this.
Can anybody help me out of this.
for e.g. pressing Ctrl+C for the first time should... (2 Replies)
Hi Gurus,
I am having 2 parameters as below
parm1=value1
parm2=parm1
I want to evaluate parm1 value using eval echo \$$parm2 and later i want to assign this value to other variable which i will be using in if statement like :
if ]; then
do this.......
fi
could you please suggest... (5 Replies)
I have file called myfile which has the text "myserver" in it. I need to have a command to ping "myserver". How would I do that?
I tried
when I type at the terminal I get the output as . How do I do something like a ?
thanks,
Nick (5 Replies)
Hi all,
some small script with eval turned me to crazy.
my OS is linux
Linux s10-1310 2.6.16.53-0.8.PTF.434477.3.TDC.0-smp #1 SMP Fri Aug 31 06:07:27 PDT 2007 x86_64 x86_64 x86_64 GNU/Linux
below script works well
#!/bin/bash
eval ssh remotehost date
eval ssh remotehost ls
below... (1 Reply)
Hi All,
I read the above written code (perl code) in another perl script and evaluates this code for each line of text file,but using exit statement in code make this not to work and i could not get the desired results. However if i use return it works fine. I just need to know why it doesn't... (1 Reply)
When i run the command sudo /usr/sbin/prtdiag manually on a solaris 10 box, it works as expected.
But the same command from my java code gives me the following error. picl_initialize failed: Daemon not responding.
I am unable to figure out why is not running from my code.:wall: (3 Replies)
Hi,
I am trying to use eval command to evaluate a variable(HAPROXY_LISTENER_rabbitmq_project-test-BRHM_PORT) which consists of '-' but unfortunately the eval command is unable to interpret the value of variable and trims the variable name after '-' and produces the string output rather than the... (10 Replies)
Discussion started by: Kuldip
10 Replies
LEARN ABOUT CENTOS
trace-cmd-check-events
TRACE-CMD-CHECK_EV(1)TRACE-CMD-CHECK_EV(1)NAME
trace-cmd-check-events - parse the event formats on local system
SYNOPSIS
trace-cmd check-events [OPTIONS]
DESCRIPTION
The trace-cmd(1) check-events parses format strings for all the events on the local system. It returns whether all the format strings can
be parsed correctly. It will load plugins unless specified otherwise.
This is useful to check for any trace event format strings which may contain some internal kernel function references which cannot be
decoded outside of the kernel. This may mean that either the unparsed format strings of the trace events need to be changed or that a
plugin needs to be created to parse them.
OPTIONS -N - Don't load plugins
SEE ALSO trace-cmd(1), trace-cmd-record(1), trace-cmd-report(1), trace-cmd-stop(1), trace-cmd-extract(1), trace-cmd-reset(1), trace-cmd-split(1),
trace-cmd-list(1), trace-cmd-listen(1), trace-cmd-start(1)AUTHOR
Written by Vaibhav Nagarnaik, <vnagarnaik@google.com[1]>
RESOURCES
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/trace-cmd.git
COPYING
Copyright (C) 2011 Google, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL).
NOTES
1. vnagarnaik@google.com
mailto:vnagarnaik@google.com
06/11/2014 TRACE-CMD-CHECK_EV(1)