I have BusyBox v1.21.0 installed and it has got very basic grep operation, no --line-buffered option
grep sync_complete /var/log/messages
tail -f /var/log/messages | grep sync_complete
is it possible to combine above commands into single line command? thanks!
Use -n +1 to make tail read the file from the start:
tail -n +1 -f /var/log/messages | grep sync_complete
Related
I have the following in a bash script file watcher.sh.
grep ERROR $ExampleLogFile > $ErrorLogFile
When I run this, it copied the lines from ExampleLogFile to ErrorLogFile that contain ERROR successfully.
I need to make it so it continually monitors the ExampleLogFile for changes and writes those to the ErrorLogFile.
I was thinking of doing the following, but this doesn't work:
tail -f grep ERROR $ExampleLogFile > $ErrorLogFile
It does write some of the lines, but its not the ones containing ERROR.
tail: grep: No such file or directory
tail: ERROR: No such file or directory
Any advise please.
You can use tee command here.
tail -f $ExampleLogFile | grep --line-buffered ERROR | tee $ErrorLogFile
It will store and print to stdout at the same time.
You need:
while :; do grep ERROR $ExampleLogFile > $ErrorLogFile; sleep 2; done
This should achieve what you want without needing the tail command.
If the file will ever be cleared though this will not work as you might expect because the grep will pull only current entries in the $ErrorLogFile.
You can arrange the tail/grep in a pipe
tail -f $ExampleLogFile | grep ERROR > $ErrorLogFile
Remember that this command will never exit by itself (tail will continue to look for additional data). You will have to arrange for some other exit condition (e.g., timeout, explicit kill, etc).
tail -f $ExampleLogFile | grep --line-buffered ERROR > $ErrorLogFile
or paranoic:
stdbuf -oL tail -f $ExampleLogFile | stdbuf -oL grep --line-buffered ERROR > $ErrorLogFile
But most probably you want to include existing lines too. In that case:
tail -n +1 -f $ExampleLogFile | grep --line-buffered ERROR > $ErrorLogFile
I'm working on a server and to show detailed GPU information I use these commands:
nvidia-smi
ps -up `nvidia-smi |tail -n +16 | head -n -1 | sed 's/\s\s*/ /g' | cut -d' ' -f3`
However as you can see, nvidia-smi is called twice. How can I make the output of nvidia-smi go to output and pipe to another command at the same time?
Use tee:
ps -up `nvidia-smi |tee /dev/stderr |tail -n +16 | head -n -1 | sed 's/\s\s*/ /g' | cut -d' ' -f3`
Since stdout is piped, you can't make a copy to it, so I picked stderr to show output.
If /dev/stderr is not available, use /proc/self/fd/2.
I'm currently monitoring a log file and my ultimate goal is to write a script that uses tail -n0 -f and execute a certain command once grep finds a correspondence. My current code:
tail -n 0 -f $logfile | grep -q $pattern && echo $warning > $anotherlogfile
This works but only once, since grep -q stops when it finds a match. The script must keep searching and running the command, so I can update a status log and run another script to automatically fix the problem. Can you give me a hint?
Thanks
use a while loop
tail -n 0 -f "$logfile" | while read LINE; do
echo "$LINE" | grep -q "$pattern" && echo "$warning" > "$anotherlogfile"
done
awk will let us continue to process lines and take actions when a pattern is found. Something like:
tail -n0 -f "$logfile" | awk -v pattern="$pattern" '$0 ~ pattern {print "WARN" >> "anotherLogFile"}'
If you need to pass in the warning message and path to anotherLogFile you can use more -v flags to awk. Also, you could have awk take the action you want instead. It can run commands via the system() function where you pass the shell command to run
I have very simple bash script:
#!/bin/bash
echo -n "A: ";
grep -v ">" | grep -o "A" $1 | wc -l;
I type
./script.sh 1.fasta
I got
A: 131
But the curcor is still blicking and my script is not finishing. What's wrong here?
Thank you.
This is the problem command:
grep -v ">" | grep -o "A" $1 | wc -l;
Since first command grep -v ">" is waiting for the input from STDIN as you haven't supplied any file to be searched by grep.
PS: Even grep -o "A" $1 is also problem since piped command will take input from output of the previous command in chain.
Probably you meant:
grep -v ">" "$1" | grep -o "A" | wc -l
Your first grep does not have a file argument so it will read from standard input:
grep -v ">" | grep -o "A" $1 | wc -l;
(read stdin) (read $1)
The reason why you get the 131 is because your second grep does have a file argument so it's getting all lines in $1 that have an A. However it's still waiting around for the end of the first grep to finish (which you can do with CTRL-D).
What you probably wanted to do is this:
grep -v ">" "$1" | grep -o "A" | wc -l
This will find all lines in $1 without a >, then all occurrences of A in that, counting them.
I want to beep a Sound , incase there is any Exception ocured in Log Files .
I am using bash script .
But unfortunately when tail is used in combintaion with sed , it doesn't work .
I have tried with the below commands and posting here .
tail -f mylogs.log | grep "Exception" | sed -e $'s/Exception/Exception\a/'
tail -f mylogs.log | sed -e $'s/Exception/Exception\a/'
tail -f mylogs.log | grep "Exception" | sed -e $'s/Exception/Exception\a/'
The problem is that grep sees that it's not writing to the terminal, so it buffers its output, eventually writing big chunks that sed can process all at once. To tell it to print out lines as soon as they're available, use the --line-buffered option:
tail -f mylogs.log \
| grep --line-buffered Exception \
| sed -u -e $'s/Exception/Exception\a/'
(Note that I've also added the -u flag to sed, which is similar to grep's --line-buffered option. In my testing it didn't seem to make a difference for this command, but I figure it's better to include it just in case.)