I am trying to redirect the output of a continuously running program to a file say error_log.
The command I am using looks like this, where myprogram.sh runs continuously generating data and writing to /var/log/httpd/error_log
myprogram.sh >> /var/log/httpd/error_log
Now I am using logrotate to rotate this file per hour. I am using create command in logrotate so that it renames the original file and creates a new one.
The logrotate config looks like
/var/log/httpd/error_log {
# copytruncate
create
rotate 4
dateext
missingok
ifempty
.
.
.
}
But here redirection fails. What I want is myprogram.sh to write data to error_log file irrespective of it being rotated by logrotate, obviously to newly generated error_log file
Any idea how to make redirection work based on the file name and not the descriptor ?
OR
Any other way of doing it in bash ?
If I understood your problem, one solution (without modify myprogram.sh) could be:
$ myprogram.sh | while true; do head -10 >> /var/log/httpd/error_log; done
Explaining:
myprogram.sh writes to stdout
We redirect this output to while bash sentence through a pipe |.
while true is an infinite loop that will never end, nor even when myprogram.sh ends which should break the pipe.
In each loop head command is called to append the first 10 lines read from the pipe to the end of current /var/log/httpd/error_log file (that may be different from the last loop because of logrotate).
(You can change the number of lines being written in each loop)
And another way is:
$ myprogram.sh | while read line; do echo "$line" >> /var/log/httpd/error_log; done
That's very similar to the first one, but this ends the loop when myprogram.sh ends or closes it's stdout.
It works line by line instead in groups of lines.
Related
Can someone fix this for me.
It should copy a version log file to backup after moving to a repo directory
Then it automatically appends line given as input to the log file with some formatting.
That's it.
Assume existence of log file and test directory.
#!/bin/bash
cd ~/Git/test
cp versionlog.MD .versionlog.MD.old
LOGDATE="$(date --utc +%m-%d-%Y)"
read -p "MSG > " VHMSG |
VHENTRY="- **${LOGDATE}** | ${VHMSG}"
cat ${VHENTRY} >> versionlog.MD
shell output
virufac#box:~/Git/test$ ~/.logvh.sh
MSG > testing script
EOF
EOL]
EOL
e
E
CTRL + C to get out of stuck in reading lines of input
virufac#box:~/Git/test$ cat versionlog.MD
directly outputs the markdown
# Version Log
## version 0.0.1 established 01-22-2020
*Working Towards Working Mission 1 Demo in 0.1 *
- **01-22-2020** | discovered faker.Faker and deprecated old namelessgen
EOF
EOL]
EOL
e
E
I finally got it to save the damned input lines to the file instead of just echoing the command I wanted to enter on the screen and not executing it. But... why isn't it adding the lines built from the VHENTRY variable... and why doesn't it stop reading after one line sometimes and this time not. You could see I was trying to do something to tell it to stop reading the input.
After some realizing a thing I had done in the script was by accident... I tried to fix it and saw that the | at the end of the read command was seemingly the only reason the script did any of what it did save to the file in the first place.
I would have done this in python3 if I had know this script wouldn't be the simplest thing I had ever done. Now I just have to know how you do it after all the time spent on it so that I can remember never to think a shell script will save time again.
Use printf to write a string to a file. cat tries to read from a file named in the argument list. And when the argument is - it means to read from standard input until EOF. So your script is hanging because it's waiting for you to type all the input.
Don't put quotes around the path when it starts with ~, as the quotes make it a literal instead of expanding to the home directory.
Get rid of | at the end of the read line. read doesn't write anything to stdout, so there's nothing to pipe to the following command.
There isn't really any need for the VHENTRY variable, you can do that formatting in the printf argument.
#!/bin/bash
cd ~/Git/test
cp versionlog.MD .versionlog.MD.old
LOGDATE="$(date --utc +%m-%d-%Y)"
read -p "MSG > " VHMSG
printf -- '- **%s** | %s\n' "${LOGDATE}" "$VHMSG" >> versionlog.MD
I made a shell script the purpose of which is to find files that don't contain a particular string, then display the first line that isn't empty or otherwise useless. My script works well in the console, but for some reason when I try to direct the output to a .txt file, it comes out empty.
Here's my script:
#!/bin/bash
# takes user input.
echo "Input substance:"
read substance
echo "Listing media without $substance:"
cd media
# finds names of files that don't feature the substance given, then puts them inside an array.
searchresult=($(grep -L "$substance" *))
# iterates the array and prints the first line of each - contains both the number and the medium name.
# however, some files start with "Microorganisms" and the actual number and name feature after several empty lines
# the script checks for that occurence - and prints the first line that doesnt match these criteria.
for i in "${searchresult[#]}"
do
grep -m 1 -v "Microorganisms\|^$" $i
done >> output.txt
I've tried moving the >>output.txt to right after the grep line inside the loop, tried switching >> to > and 2>&1, tried using tee. No go.
I'm honestly feeling utterly stuck as to what the issue could be. I'm sure there's something I'm missing, but I'm nowhere near good enough with this to notice. I would very much appreciate any help.
EDIT: Added files to better illustrate what I'm working with. Sample inputs I tried: Glucose, Yeast extract, Agar. Link to files [140kB] - the folder was unzipped beforehand.
The script was given full permissions to execute. I don't think the output is being rewritten because even if I don't iterate and just run a single line of the loop, the file is empty.
I am new to Shellscripting.I am working on a poc in which a script should read a log file and then append to a existing file for the purpose of alert.It should work as per below
There will be some predefined format according to which it will decide whether to append in file or not.For example:
WWXXX9999XS message
**XXX** - is a 3 letter acronym (application code) like for **tom** for tomcat application
9999 - is a 4 numeric digit in the range 1001-1999
**E or X** - For notification X ,If open/active alerts already existing for same error code and same message,new alerts will not be raised for existing one.Once you have closed existing alerts,it will raise alarm for new error.There is any change in message for same error code from existing one, it will raise a alarm even though open/active alerts present.
X option is only for drop duplicates on code and message otherwise all alert mechanisms are same.
**S** - is the severity level, I.e 2,3
**message** - is any text that will be displayed
The script will examine the log file, and look for error like cloud server is down,then it would append 'wwclo1002X2 cloud server is down'if its a new alert.
2.If the same alert is coming again,then it should append 'wwclo1002E2 cloud server is down
There are some very handy commands you can use to do this type of File manipulation. I've updated this in response to your comment to allow functionality that will check if the error has already been appended to the new file.
My suggestion would be that there is enough functionality here to warrant saving it in a bash script.
My approach would be to use a combination of less, grep and > to read and parse the file and then append to the new file. First save the following into a bash script (e.g. a file named script.sh)
#!/bin/bash
result=$(less $1 | grep $2)
exists=$(less $3 | grep $2)
if [[ "$exists" == "$result" ]]; then
echo "error, already present in file"
exit 1
else
echo $result >> $3
exit 0
fi
Then use this file in the command passing in the log file as the first argument, the string to search for as the second argument and the target results file as the third argument like this:
./script.sh <logFileName> "errorToSearchFor" <resultsTargetFileName>
Don't forget to run the file you will need to change the permissions - you can do this using:
chmod u+x script.sh
Just to clarify as you have mentioned you are new to scripting - the less command will output the entire file, the | command (an unnamed pipe) will pass this output to the grep command which will then search the file for the expression in quotes and return all lines from the file containing that expression. The output of the grep command is then appended to the new file with >>.
You may need to tailor the expression in quotes after grep to get exactly the output you want from the log file.
The filenames are just placeholders, be sure to update these with the correct file names. Hope this helps!
Note updated > to >> (single angle bracket overwrites, double angle bracket appends
I have large file with size of 130GB.
# ls -lrth
-rw-------. 1 root root 129G Apr 20 04:25 syslog.log
So I need to reduce file size by deleting line which starts with "Nov 2" , So I have given the following command,
sed -i '/Nov 2/d' syslog.log
So I can't edit file using VIM editor also.
When I trigger SED command , its creating backup file also. But I don't have much space in root. Please try to give alternate solution to delete particular line from this file without increasing space in server.
It does not create a real backup file. sed is a stream editor. When applied to a file with option -i it will stream that file through the sed process, write the output to a new file (a temporary one), when everything is done, it will rename the new file to the original name.
(There are options to create backup files also, but you didn't give them, so I won't mention that further.)
In your case you have a very large file and don't want to create any copy, however temporary. For this you need to open the file for reading and writing at the same time, then your sed process can overwrite the original. After this, you will have to truncate the file at the end of the writing.
To demonstrate how this can be done, we first perform a test case.
Create a test file, containing lots of lines:
seq 0 999999 > x
Now, lets say we want to remove all lines containing the digit 4:
grep -v 4 1<>x <x
This will open the file for reading and writing as STDOUT (1), and for reading as STDIN. The grep command will read all lines and will output only the lines not containing a 4 (option -v).
This will effectively overwrite the beginning of the original file.
You will not know how long the output is, so after the output the original contents of the file will appear:
…
999991
999992
999993
999995
999996
999997
999998
999999
537824
537825
537826
537827
537828
537829
…
You can use the Unix tool truncate to shorten your file manually afterwards. In a real scenario you will have trouble finding the right spot for this, so it makes sense to count the number of bytes written (using wc):
(Don't forget to recreate the original x for this test.)
(grep -v 4 <x | tee /dev/stderr 1<>x) |& wc -c
This will preform the step above and additionally print out the number of bytes written to the terminal, in this example case the output will be 3653658. Now use truncate:
truncate -s 3653658 x
Now you have the result you want.
If you want to do this in a script, i. e. without interaction, you can use this:
length=$((grep -v 4 <x | tee /dev/stderr 1<>x) |& wc -c)
truncate -s "$length" x
I cannot guarantee that this will work for files >2GB or >4GB on your machine; depending on your operating system (32bit?) and the versions of the installed tools you might run into largefile issues. I'd perform tests with large files first (>4GB as this is typically a limit for many things) and then cross your fingers and give it a try :)
Some caveats you have to keep in mind:
Of course, nobody is supposed to append log entries to that log file while the procedure is running.
Also, any abort during the running of the process (power failure, signal caught, etc.) will leave the file in an undefined state. But re-running the command again after such a mishap will in most cases produce the correct output; some lines might be doubled, but not more than a single line should be corrupted then.
The output must be smaller than the input, of course, otherwise the writing will overtake the reading, corrupting the whole result so that lines which should be there will be missing (or truncated at the start).
I'm trying to redirect(?) my standard error/output to a text file.
I did my research, but for some reason the online answers are not working for me.
What am I doing wrong?
cd /home/user1/lists/
for dir in $(ls)
do
(
echo | $dir > /root/user1/$dir" "log.txt
) > /root/Desktop/Logs/Update.log
done
I also tried
2> /root/Desktop/Logs/Update.log
1> /root/Desktop/Logs/Update.log
&> /root/Desktop/Logs/Update.log
None of these work for me :(
Help please!
Try this for the basics:
echo hello >> log.txt 2>&1
Could be read as: echo the word hello, redirecting and appending STDOUT to the file log.txt. STDERR (file descriptor 2) is redirected to wherever STDOUT is being pointed. Note that STDOUT is the default and thus there is no "1" in front of the ">>". Works on the current line only.
To redirect and append all output and error of all commands in a script, put this line near the top. It will be in effect for the length of the script instead of doing it on each line:
exec >>log.txt 2>&1
If you are trying to obtain a list of the files in /home/user1/lists, you do not need a loop at all:
ls /home/usr1/lists/ >Update.log
If you are attempting to run every file in the directory as an executable with a newline as its input, and collect the output from all these programs in Update.log, try this:
for file in /home/user1/lists/*; do
echo | "$file"
done >Update.log
(Notice how we avoid the useless use of ls and how there is no redirection inside the loop.)
If you want to create an empty file called *.log.txt for each file in the directory, you would do
for file in /home/user1/lists/*; do
touch "$(basename "$file")"log.txt
done
(Using basename to obtain the file name without the directory part avoids the cd but you could do it the other way around. Generally, we tend to avoid changing the directory in scripts, so that the tool can be run from anywhere and generate output in the current directory.)
If you want to create a file containing a single newline, regardless of whether it already exists or not,
for file in /home/user1/lists/*; do
echo >"$(basename "$file")"log.txt
done
In your original program, you redirect the echo inside the loop, which means that the redirection after done will not receive any output at all, so the created file will be empty.
These are somewhat wild guesses at what you might actually be trying to accomplish, but should hopefully help nudge you slightly in the right direction. (This should properly be a comment, I suppose, but it's way too long and complex.)