06-21-2010
Thanks. I get that since all the special symbols like |,",',; all are evaluated before substitution takes place. Hence, in the case of $cmd, since no specia symbols were initially found, cmd was substituted for "date | wc" and | was taken as an argument to date (as | now has no meaning).
One question though, why do call evaluating the special symbols like | as expanding it? Does it mean that a special code for these symbols is inserted there when they're expanded ?
Also, it seems that there is another function of eval. When there are no substitutions to be made, then eval just removes the special symbols like '' and backslash. Like in the following :
eval echo \\l
eval echo \\\k
eval echo 'h'
I'm using bash shell
Last edited by daudiam; 06-21-2010 at 12:46 AM..
10 More Discussions You Might Find Interesting
1. Shell Programming and Scripting
Hi
i have the following code:
if(($line!=1) and (@field!='\$')){
print ( "\nTRY TO CONNECT TO DATABASE................\n");
my $dbh = DBI->connect($dsn, $user, $pass);
print ("CONNECTED TO DATABASE\n");
eval
... (1 Reply)
Discussion started by: chriss_58
1 Replies
2. Shell Programming and Scripting
Hi All,
i have an issue regarding trap command.
i have specified trap function in the beginning of the script to catch some signals but in the later part of the script i want to remove the effect of this.
Can anybody help me out of this.
for e.g. pressing Ctrl+C for the first time should... (2 Replies)
Discussion started by: vikas_kesarwani
2 Replies
3. Shell Programming and Scripting
Hi Gurus,
I am having 2 parameters as below
parm1=value1
parm2=parm1
I want to evaluate parm1 value using eval echo \$$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)
Discussion started by: k_vikash
5 Replies
4. Shell Programming and Scripting
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)
Discussion started by: nikhilfake
5 Replies
5. Shell Programming and Scripting
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)
Discussion started by: summer_cherry
1 Replies
6. Shell Programming and Scripting
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)
Discussion started by: sarbjit
1 Replies
7. Solaris
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)
Discussion started by: randeepsp
3 Replies
8. Shell Programming and Scripting
anyone has any info on why this is complaining???
vivek@vivek-c5e55ef2e ~/TAC
$ zoneCounter=1
vivek@vivek-c5e55ef2e ~/TAC
$ optUsage1=23%
vivek@vivek-c5e55ef2e ~/TAC
$ eval eval echo "<th>Zone $zoneCounter </th><th align=\"left\"> \$optUsage$zoneCounter </th>"
-bash: syntax error... (1 Reply)
Discussion started by: vivek d r
1 Replies
9. Shell Programming and Scripting
anyone has any info on why this is complaining???
vivek@vivek-c5e55ef2e ~/TAC
$ zoneCounter=1
vivek@vivek-c5e55ef2e ~/TAC
$ optUsage1=23%
vivek@vivek-c5e55ef2e ~/TAC
$ eval eval echo "<th>Zone $zoneCounter </th><th align=\"left\"> \$optUsage$zoneCounter </th>"
-bash: syntax error... (13 Replies)
Discussion started by: vivek d r
13 Replies
10. Shell Programming and Scripting
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-hist
TRACE-CMD-HIST(1) TRACE-CMD-HIST(1)
NAME
trace-cmd-hist - show histogram of events in trace.dat file
SYNOPSIS
trace-cmd hist [OPTIONS][input-file]
DESCRIPTION
The trace-cmd(1) hist displays a histogram form from the trace.dat file. Instead of showing the events as they were ordered, it creates a
histogram that can be displayed per task or for all tasks where the most common events appear first. It uses the function tracer and call
stacks that it finds to try to put together a call graph of the events.
OPTIONS
-i input-file
By default, trace-cmd hist will read the file trace.dat. But the -i option open up the given input-file instead. Note, the input file
may also be specified as the last item on the command line.
-P
To compact all events and show the call graphs by ignoring tasks and different PIDs, add the -P to do so. Instead of showing the task
name, it will group all chains together and show "<all pids>".
SEE ALSO
trace-cmd(1), trace-cmd-record(1), trace-cmd-report(1), trace-cmd-start(1), trace-cmd-stop(1), trace-cmd-extract(1), trace-cmd-reset(1),
trace-cmd-split(1), trace-cmd-listen(1)
AUTHOR
Written by Steven Rostedt, <rostedt@goodmis.org[1]>
RESOURCES
git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/trace-cmd.git
COPYING
Copyright (C) 2010 Red Hat, Inc. Free use of this software is granted under the terms of the GNU Public License (GPL).
NOTES
1. rostedt@goodmis.org
mailto:rostedt@goodmis.org
06/11/2014 TRACE-CMD-HIST(1)