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Ideas for while loop

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# 1  
Old 10-05-2014
Ideas for while loop
idealy, i'd like to do something like this:

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

but when i do, i get an unexpected response. i.e.

Code:
cat test:

#!/bin/sh

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

## ./test

when i run the above, while it does print each line, at the very end, it prints the following error message:

i get an error at the last line that says:

Code:
: File name too long

i'm using the above method because it appears to be faster than this:
Code:
egrep error /var/log/syslog | while read line
do
        echo $line
done

# 2  
Old 10-06-2014
What's wrong with a simple
Code:
egrep error /var/log/syslog

???
This User Gave Thanks to achenle For This Post:
rbatte1
# 3  
Old 10-06-2014
I think the while loop is expecting a filename.

you could redirect the output to a file
Code:
egrep error /var/log/syslog > /tmp/error.out

while read line
do
        echo $line
done < /tmp/error.out

rm /tmp/error.out

Last edited by ongoto; 10-06-2014 at 12:57 AM.. Reason: forgot code tags
This User Gave Thanks to ongoto For This Post:
SkySmart
# 4  
Old 10-06-2014
Assuming the echo $line is nothing more that a place holder test, if your shell supports it.
Code:
while read line
do
    echo $line
done < <(egrep error /var/log/syslog)

This User Gave Thanks to Aia For This Post:
SkySmart
# 5  
Old 10-06-2014
Quote:
Originally Posted by SkySmart
idealy, i'd like to do something like this:

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

but when i do, i get an unexpected response. i.e.

Code:
 
cat test:
 
#!/bin/sh
 
while read line
do
        echo $line
done < $(egrep error /var/log/syslog)
 
## ./test

when i run the above, while it does print each line, at the very end, it prints the following error message:

i get an error at the last line that says:

Code:
: File name too long

i'm using the above method because it appears to be faster than this:
Code:
egrep error /var/log/syslog | while read line
do
        echo $line
done

Hello SkySmart,

Could you please try following and let me know if this helps.

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

Thanks,
R. Singh
Last edited by RavinderSingh13; 10-06-2014 at 01:57 AM..
This User Gave Thanks to RavinderSingh13 For This Post:
SkySmart
# 6  
Old 10-06-2014
Quote:
Originally Posted by RavinderSingh13
Hello SkySmart,

Could you please try following and let me know if this helps.

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

Thanks,
R. Singh
i tried this. got the same error.
# 7  
Old 10-06-2014
The loop expects a file after the redirect of stdin (<), which command substitution will not provide (unless the file happens to contain a single filename). Try a redirect through a pipe:
Code:
egrep error /var/log/syslog | 
while read -r line
do
  printf "%s\n"  "$line"
done

or in bash / ksh93 / zsh you can also provide a constructed file like this (process substitution) if you want:
Code:
while read -r line
do
  printf "%s\n"  "$line"
done < <(egrep error /var/log/syslog)

Edit : Just noticed Aia already suggested something similar to the latter option..
Last edited by Scrutinizer; 10-06-2014 at 02:43 AM..
This User Gave Thanks to Scrutinizer For This Post:
SkySmart
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