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Ideas for while loop

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# 8  
Old 10-06-2014
Assuming that your shells supports it, you can get away from calling an external program like egrep for such a simple match
Code:
while read -r line
do
  [[ $line =~ error ]] && echo $line
done < /var/log/syslog

Again, this is all assuming that the echo $line is nothing more that a place holder or test for what it would be a real `do something meaningful', otherwise is silly.
Last edited by Aia; 10-06-2014 at 02:46 AM.. Reason: clarifying again.
This User Gave Thanks to Aia For This Post:
SkySmart
# 9  
Old 10-06-2014
Quote:
Originally Posted by SkySmart
i tried this. got the same error.
Hello SkySmart,

We can follow simple way here too by redirecting the egrep output to a file and then we can take input from that file as follows. Offcourse finding other ways is good too for our learning.

Code:
egrep error /var/log/syslog > Error_Details.txt
while read line
do
     echo "$line"
done < Error_Details.txt

Or we can simply use egrep error /var/log/syslog in script itself Smilie.

Thanks,
R. Singh
Last edited by rbatte1; 10-06-2014 at 09:42 AM.. Reason: Lower case for commands in the shell script.
This User Gave Thanks to RavinderSingh13 For This Post:
SkySmart
# 10  
Old 10-06-2014
I'm still confused as to what the end requirement is. If you want to extract records to display on the screen, the egrep by itself will do that. If you need to use a loop to do something else with the records, then save the IO cost, the disk space and the time with:-
Code:
egrep error /var/log/syslog | while read line
do
     echo "Processing line \"$line\""
     # Do whatever else here......
done

You will need to be careful that any nested loops don't gobble up your input to this loop.


Anyway, what are you trying to achieve?



Kind regards,
Robin
This User Gave Thanks to rbatte1 For This Post:
SkySmart
# 11  
Old 10-06-2014
Quote:
Originally Posted by rbatte1
I'm still confused as to what the end requirement is. If you want to extract records to display on the screen, the egrep by itself will do that. If you need to use a loop to do something else with the records, then save the IO cost, the disk space and the time with:-
Code:
egrep error /var/log/syslog | while read line
do
     echo "Processing line \"$line\""
     # Do whatever else here......
done

You will need to be careful that any nested loops don't gobble up your input to this loop.


Anyway, what are you trying to achieve?



Kind regards,
Robin
i have to run a while loop and it is very important to me that i find the method that is the quickest.

The methods below appear to be the fastest, but, while they loop through the file, they error out at the end, complaining about file name too long:

Code:
while read line
do
    echo $line
done < <(egrep error /var/log/syslog)

Code:
while read line
do
    echo $line
done < "$(egrep error /var/log/syslog)"

# 12  
Old 10-07-2014
I don't understand. The first method should work (if the shell supports it) and cannot complain that the filename is too long (unless this is literally somewhere in the text of your syslog file Smilie )
If the shell does not support it, it will give a syntax error.


The second method is wrong and will not work and will produce that error.


--
BTW. it is best to quote $line ( echo "$line" )
# 13  
Old 10-07-2014
Hi,
Another way:
Code:
while read line
do
    echo "$line"
done <<_EOF
$(egrep error /var/log/syslog)
_EOF

Regards.
This User Gave Thanks to disedorgue For This Post:
SkySmart
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