This is an issue caused with the way bash implements pipes. When piping input to a while, I believe that bash executed the while in a child processes which causes any changes to variables inside of the while to be lost.
This is one reason I prefer kshell over bash. If you have a modern kshell, I suggest you use it. If not then try writing your output to a temp file and reading it into the while.
Try this in both shells to see the difference. Ksh gets the answer right after the loop both times.
Last edited by agama; 11-07-2011 at 12:45 AM..
Reason: typo
Hi...
i am trying to ping my servers .The hostnames are present in a file .They are separated by spaces in the file .
i am doing the following :
a=1
for name in $(cat host2 |cut -d" " -f$a)
do
echo Pinging server $name
ping -c5 $name
a=$a+1
done
It is... (3 Replies)
i have these data in a variable "$test"
BUNGA TERATAI 3 5055 ITH 1 1
JADE TRADER 143W ITH 4 4
MOL SPLENDOR 0307A ITH 3 3
the red coloured are the ones that i want to take and compare
what I need to do is to take out the red coloured and then compare to another variable, if same then... (0 Replies)
Hi,
Is it possible to assign one variable to other.
eg.
v1="table1"
v2="20000"
I want table1 to assign 20000
table1=20000
Is there any way?
Thanks (2 Replies)
Hi
I have webserver that I do read data from.
Data are stored like this:
Huston |1
Portland |2
Hazen |1
Minneapolis |4
Albany |1
Pittsburg |1
Albany |1
Huston |1
Portland|1
Hazen |2
Albany |2
Huston |1
Hazen |1
Script #!/bin/sh
user="admin" (1 Reply)
Hello all,
I find it hard to explain what I need so I will post the code
OVZINCLUDE="16810 16811 1689"
PLUS_16810="test"
PLUS_16811="test"
for VPS in $OVZINCLUDE
do
echo "Dumping VPSes: $OVZINCLUDE "
vzdump --compress --snapshot ${PLUS_$VPS} $VPS
done
... (2 Replies)
Simple enough problem I think, I just can't seem to get it right.
The below doesn't work as intended, it's just a function defined in a much larger script:
CheckValues() {
for field in \
Group_ID \
Group_Title \
Rule_ID \
Rule_Severity \
... (2 Replies)
I have a group of variables myLINEcnt1 - myLINEcnt10. I'm trying to printout the values using a for loop. I am at the head banging stage since i'm sure it has to be a basic syntax issue that i can't figure out.
For myIPgrp in 1 2 3 4 5 6 7 8 9 10; do
here i want to output the value of... (4 Replies)
Hello guys,
This truly is a newbie question. I'm trying to make a loop to execute simultaneous commands indefinitely while using variable. Here is how my mess looks like (this is just an example):
#!/bin/bash
IP=`shuf -n 1 IP.txt` # I figured this would be easier to select random lines... (4 Replies)
Hello All,
Maybe I'm Missing something here but I have NOOO idea what the heck is going on with this....?
I have a Variable that contains a PATTERN of what I'm considering "Illegal Characters". So what I'm doing is looping
through a string containing some of these "Illegal Characters". Now... (5 Replies)
Hi All,
I have a file which has hundred of records with fixed number of fields. In each record there is set of 8 characters which represent the duration of that activity. I want to sum up the duration present in all the records for a report. The problem is the duration changes per record so I... (5 Replies)
Discussion started by: danish0909
5 Replies
LEARN ABOUT REDHAT
system
SYSTEM(3) Linux Programmer's Manual SYSTEM(3)NAME
system - execute a shell command
SYNOPSIS
#include <stdlib.h>
int system(const char *string);
DESCRIPTION
system() executes a command specified in string by calling /bin/sh -c string, and returns after the command has been completed. During
execution of the command, SIGCHLD will be blocked, and SIGINT and SIGQUIT will be ignored.
RETURN VALUE
The value returned is -1 on error (e.g. fork failed), and the return status of the command otherwise. This latter return status is in the
format specified in wait(2). Thus, the exit code of the command will be WEXITSTATUS(status). In case /bin/sh could not be executed, the
exit status will be that of a command that does exit(127).
If the value of string is NULL, system() returns nonzero if the shell is available, and zero if not.
system() does not affect the wait status of any other children.
CONFORMING TO
ANSI C, POSIX.2, BSD 4.3
NOTES
As mentioned, system() ignores SIGINT and SIGQUIT. This may make programs that call it from a loop uninterruptable, unless they take care
themselves to check the exit status of the child. E.g.
while(something) {
int ret = system("foo");
if (WIFSIGNALED(ret) &&
(WTERMSIG(ret) == SIGINT || WTERMSIG(ret) == SIGQUIT))
break;
}
Do not use system() from a program with suid or sgid privileges, because strange values for some environment variables might be used to
subvert system integrity. Use the exec(3) family of functions instead, but not execlp(3) or execvp(3). system() will not, in fact, work
properly from programs with suid or sgid privileges on systems on which /bin/sh is bash version 2, since bash 2 drops privileges on
startup. (Debian uses a modified bash which does not do this when invoked as sh.)
The check for the availability of /bin/sh is not actually performed; it is always assumed to be available. ISO C specifies the check, but
POSIX.2 specifies that the return shall always be non-zero, since a system without the shell is not conforming, and it is this that is
implemented.
It is possible for the shell command to return 127, so that code is not a sure indication that the execve() call failed.
SEE ALSO sh(1), signal(2), wait(2), exec(3)
2001-09-23 SYSTEM(3)