Typically I'd use > /var/log/snort/alert however on FreeBSD this doesn't work. 'Invalid null command' error is thrown. Any way to do this other than deleting and making a new file?
This should work canonically on all Unix-like systems: echo > /path/to/file. Most important is that the file descriptor will be retained.
For example,
shell> cat /dev/null > /var/log/snort/alert
Related
I tried gedit, nano, vi, leafpad and other text editors , it won't open, I tried cat and other file looking commands, and I ensure you it's a file not a directory!
This type of approach has a lot of misunderstanding because using - as an argument refers to STDIN/STDOUT i.e dev/stdin or dev/stdout .So if you want to open this type of file you have to specify the full location of the file such as ./- .For eg. , if you want to see what is in that file use cat ./-
Both cat < - and ./- command will give you the output
you can use redirection
cat < -file_name
It looks like the rev command doesn't treat - as a special character.
From the man page
The rev utility copies the specified files to standard output, reversing the order of characters in every line.
so
rev - | rev
should show what's in the file in the correct order.
I tried with pico or vi command.pico readme which allowed me open in editor and read the contents.
if you want to open this type of file you have to specify the full location of the file such as ./- .For eg. , if you want to see what is in that file use cat ./-
cat ./- is the syntax that reveals the correct password for bandit the "rev -" reveals something else
I'm totally new to bash scripting but i want to solve this problem..
the command is:
objfil=`echo ${srcfil} | sed -e "s,c$,o,"`
the idea about the bash script program is to check for the source files, and check if there is an adjacent object file in the OBJ directory, if so, the rest of the program runs smoothly, if not, the iteration terminates and skips the current source file, and moves on to the next one.. it works with .c files but not on the headers, since the object filenames depend on .c files.. i want to write this command so it checks the object files not just the .c but the .h files too.. but without skipping them. i know i have to do something else too, but i need to understand what this line of command does exactly to move on. Thanks. (Sorry for my english)
UPDATE:
if test -r ${curOBJdir}/${objfil}
then
cp -v ${srcfil} ./SAVEDSRC/${srcfil}
fdone="NO"
linenums=ALL
else
fdone="YES"
err="${curOBJdir}/${objfil} is missing - ${srcfil} skipped)"
echo ${err}
echo ${err} >>${log}
fi
while test ${fdone} == "NO"
do
#rest of code ...
here is the rest of the program.. i tried to comment out the "test" part to ignore the comparison just because i only want my script to work on .h files, but without checking the e.g abc.h files has an abc.o file.. (the object file generation is needed because the end of the script there's a comparison between the hexdump of the original and modified object files). The whole script is for changing the basic types with typedefs like int to sint32_t for example.
This concrete command will substitute all c's right before line-end to o:
srcfill=abcd.c
objfil=`echo ${srcfil} | sed -e "s,c$,o,"`
echo $objfil
Output:
abcd.o
P.S. It uses a different match/replace separator: default is / but it uses ,.
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 "$file")"log.txt
done
In your original program, you redirect the echo inside the loop, which means that the redirection after done will not receive any output at all, so the created file will be empty.
These are somewhat wild guesses at what you might actually be trying to accomplish, but should hopefully help nudge you slightly in the right direction. (This should properly be a comment, I suppose, but it's way too long and complex.)
I have a written a sample script on my Mac
#!/bin/bash
test() {
echo "Example"
}
test
exit 0
and this works fine by displaying Example
When I run this script on a RedHat machine, it says
syntax error near unexpected token '
I checked that bash is available using
cat /etc/shells
which bash shows /bin/bash
Did anyone come across the same issue ?
Thanks in advance !
It could be a file encoding issue.
I have encountered file type encoding issues when working on files between different operating systems and editors - in my case particularly between Linux and Windows systems.
I suggest checking your file's encoding to make sure it is suitable for the target linux environment. I guess an encoding issue is less likely given you are using a MAC than if you had used a Windows text editor, however I think file encoding is still worth considering.
--- EDIT (Add an actual solution as recommended by #Potatoswatter)
To demonstrate how file type encoding could be this issue, I copy/pasted your example script into Notepad in Windows (I don't have access to a Mac), then copied it to a linux machine and ran it:
jdt#cookielin01:~/windows> sh ./originalfile
./originalfile: line 2: syntax error near unexpected token `$'{\r''
'/originalfile: line 2: `test() {
In this case, Notepad saved the file with carriage returns and linefeeds, causing the error shown above. The \r indicates a carriage return (Linux systems terminate lines with linefeeds \n only).
On the linux machine, you could test this theory by running the following to strip carriage returns from the file, if they are present:
cat originalfile | tr -d "\r" > newfile
Then try to run the new file sh ./newfile . If this works, the issue was carriage returns as hidden characters.
Note: This is not an exact replication of your environment (I don't have access to a Mac), however it seems likely to me that the issue is that an editor, somewhere, saved carriage returns into the file.
--- /EDIT
To elaborate a little, operating systems and editors can have different file encoding defaults. Typically, applications and editors will influence the filetype encoding used, for instance, I think Microsoft Notepad and Notepad++ default to Windows-1252. There may be newline differences to consider too (In Windows environments, a carriage return and linefeed is often used to terminate lines in files, whilst in Linux and OSX, only a Linefeed is usually used).
A similar question and answer that references file encoding is here: bad character showing up in bash script execution
try something like
$ sudo apt-get install dos2unix
$ dos2unix offendingfile
Easy way to convert example.sh file to UNIX if you are working in Windows is to use NotePad++ (Edit>EOL Conversion>UNIX/OSX Format)
You can also set the default EOL in notepad++ (Settings>Preferences>New Document/Default Directory>select Unix/OSX under the Format box)
Thanks #jdt for your answer.
Following that, and since I keep having this issue with carriage return, I wrote that small script. Only run carriage_return and you'll be prompted for the file to "clean".
https://gist.github.com/kartonnade/44e9842ed15cf21a3700
alias carriage_return=remove_carriage_return
remove_carriage_return(){
# cygwin throws error like :
# syntax error near unexpected token `$'{\r''
# due to carriage return
# this function runs the following
# cat originalfile | tr -d "\r" > newfile
read -p "File to clean ? "
file_to_clean=$REPLY
temp_file_to_clean=$file_to_clean'_'
# file to clean => temporary clean file
remove_carriage_return_one='cat '$file_to_clean' | tr -d "\r" > '
remove_carriage_return_one=$remove_carriage_return_one$temp_file_to_clean
# temporary clean file => new clean file
remove_carriage_return_two='cat '$temp_file_to_clean' | tr -d "\r" > '
remove_carriage_return_two=$remove_carriage_return_two$file_to_clean
eval $remove_carriage_return_one
eval $remove_carriage_return_two
# remove temporary clean file
eval 'rm '$temp_file_to_clean
}
I want to add to the answer above is how to check if it is carriage return issue in Unix like environment (I tested in MacOS)
1) Using cat
cat -e my_file_name
If you see the lines ended with ^M$, then yes, it is the carriage return issue.
2) Find first line with carriage return character
grep -r $'\r' Grader.sh | head -1
3) Using vim
vim my_file_name
Then in vim, type
:set ff
If you see fileformat=dos, then the file is from a dos environment which contains a carriage return.
After finding out, you can use the above mentioned methods by other people to correct your file.
I had the same problem when i was working with armbian linux and Windows .
i was trying to coppy my codes from windows to armbian and when i run it this Error Pops Up. My problem Solved this way :
1- try to Coppy your files from windows using WinSCP .
2- make sure that your file name does not have () characters
Is there way to compress the core files during core dump generation?
If the storage space is limited in the system, is there a way of conserving it in case of need for core dump generation with immediate compression?
Ideally the method would work on older versions of linux such as 2.6.x.
The Linux kernel /proc/sys/kernel/core_pattern file will do what you want: http://www.mjmwired.net/kernel/Documentation/sysctl/kernel.txt#191
Set the filename to something like |/bin/gzip -1 > /var/crash/core-%t-%p-%u.gz and your core files should be saved compressed for you.
For an embedded Linux systems, following script change perfectly works to generate compressed core files in 2 steps
step 1: create a script
touch /bin/gen_compress_core.sh
chmod +x /bin/gen_compress_core.sh
cat > /bin/gen_compress_core.sh #!/bin/sh exec /bin/gzip -f - >"/var/core/core-$1.$2.gz"
ctrl +d
step 2: update the core pattern file
cat > /proc/sys/kernel/core_pattern |/bin/gen_compress_core.sh %e %p ctrl+d
As suggested by other answer, the Linux kernel /proc/sys/kernel/core_pattern file is good place to start: http://www.mjmwired.net/kernel/Documentation/sysctl/kernel.txt#141
As documentation says you can specify the special character "|" which will tell kernel to output the file to script. As suggested you could use |/bin/gzip -1 > /var/crash/core-%t-%p-%u.gz as name, however it doesn't seem to work for me. I expect that the reason is that on my system kernel doesn't treat the > character as a output, rather it probably passes it as a parameter to gzip.
In order to avoid this problem, like other suggested you can create your file in some location I am using /home//crash/core.sh, create it using the following command, replacing with your user. Alternatively you can also obviously change the entire path.
echo -e '#!/bin/bash\nexec /bin/gzip -f - >"/home/<username>/crashes/core-$1-$2-$3-$4-$5.gz"' > ~/crashes/core.sh
Now this script will take 5 input parameters and concatenate them and add to core-path. The full paths must be specified in the ~/crashes/core.sh. Also the location of this script can be specified. Now lets tell kernel to use tour executable with parameters when generating file:
sudo sysctl -w kernel.core_pattern="|/home/<username>/crashes/core.sh %e %p %h %t"
Again should be replaced (or entire path to match location and name of core.sh script). Next step is to crash some program, lets create example crashing cpp file:
int main (){
int * a = nullptr;
int b = *a;
}
After compiling and running there are 2 options, either we will see:
Segmentation fault (core dumped)
Or
Segmentation fault
In case we see the latter, there are few possible reasons.
ulimit is not set, ulimit -c should specify what is limit for cores
apport or your distro core dump collector is not running, this should be investigated further
there is an error in script we wrote, I suggest than checking some basic dump path to check if the other things aren't reason the below should create /tmp/core.dump:
sudo sysctl -w kernel.core_pattern="/tmp/core.dump"
I know there is already an answer for this question however it wasn't obvious for me why it isn't working "out of the box" so I wanted to summarize my findings, hope it helps someone.