I am trying to get the output of hostnames based on OS type (want only RedHat server hostnames) set as a variable.
but my code keeps spitting out the string RedHat along with each hostname.
minions=$(salt-run manage.up | cut -a " " -f2)
hosts=$(for minion in ${minions[#]}; do salt ${minion} grains.items | grep "os_family:" | grep RedHat && echo ${minion}; done)
By default grep will ouput the results of the pattern match.
If your version of grep supports it ... the -q flag will suppress the output:
... | grep -q RedHat && echo ${minion}; done)
Alternatively, redirect the output to /dev/null:
... | grep RedHat >/dev/null && echo ${minion}; done)
Running my script in a terminal works fine. It also works fine in Mint 18.2 when run at boot via /etc/rc.local, but on Mint 18.1 it doesn't work. Also on 18.1 it won't run via sudo crontab -e. I'm assuming it's got something to do with the tail/grep part.
Here is the relevant part of my script - up to this point the script works;
# Takes a screen capture every time I type a string that matches one from a list
sudo -i tail -fn0 "$path"k.log | \
while read line ; do
echo "$line" | egrep --line-buffered -i -e "$pattern"
if [ $? = 0 ]
then
matches=$(echo "$line" | egrep --line-buffered -i -o "$pattern")
cap_split=$(echo "$matches" | sed -e ':a' -e 'N' -e '$!ba' -e 's/\n/ /g')
cap_string=$(echo "$cap_split" | sed -e 's/[^A-Za-z0-9\\n._-]/_/g')
sleep 1
DISPLAY=:0.0 scrot "$path"cap/"$stamp"_"$cap_string".png
echo -e "### Match found \"$cap_split\" and cap created ###"
fi
done
Why will it only work in the terminal on Mint 8.1 and not from rc.local or cron?
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
cat a.txt | xargs -I % echo %
In the example above, xargs takes echo % as the command argument. But in some cases, I need multiple commands to process the argument instead of one. For example:
cat a.txt | xargs -I % {command1; command2; ... }
But xargs doesn't accept this form. One solution I know is that I can define a function to wrap the commands, but I want to avoid that because it is complex. Is there a better solution?
cat a.txt | xargs -d $'\n' sh -c 'for arg do command1 "$arg"; command2 "$arg"; ...; done' _
...or, without a Useless Use Of cat:
<a.txt xargs -d $'\n' sh -c 'for arg do command1 "$arg"; command2 "$arg"; ...; done' _
To explain some of the finer points:
The use of "$arg" instead of % (and the absence of -I in the xargs command line) is for security reasons: Passing data on sh's command-line argument list instead of substituting it into code prevents content that data might contain (such as $(rm -rf ~), to take a particularly malicious example) from being executed as code.
Similarly, the use of -d $'\n' is a GNU extension which causes xargs to treat each line of the input file as a separate data item. Either this or -0 (which expects NULs instead of newlines) is necessary to prevent xargs from trying to apply shell-like (but not quite shell-compatible) parsing to the stream it reads. (If you don't have GNU xargs, you can use tr '\n' '\0' <a.txt | xargs -0 ... to get line-oriented reading without -d).
The _ is a placeholder for $0, such that other data values added by xargs become $1 and onward, which happens to be the default set of values a for loop iterates over.
You can use
cat file.txt | xargs -i sh -c 'command {} | command2 {} && command3 {}'
{} = variable for each line on the text file
With GNU Parallel you can do:
cat a.txt | parallel 'command1 {}; command2 {}; ...; '
For security reasons it is recommended you use your package manager to
install. But if you cannot do that then you can use this 10 seconds
installation.
The 10 seconds installation will try to do a full installation; if
that fails, a personal installation; if that fails, a minimal
installation.
$ (wget -O - pi.dk/3 || lynx -source pi.dk/3 || curl pi.dk/3/ || \
fetch -o - http://pi.dk/3 ) > install.sh
$ sha1sum install.sh | grep 883c667e01eed62f975ad28b6d50e22a
12345678 883c667e 01eed62f 975ad28b 6d50e22a
$ md5sum install.sh | grep cc21b4c943fd03e93ae1ae49e28573c0
cc21b4c9 43fd03e9 3ae1ae49 e28573c0
$ sha512sum install.sh | grep da012ec113b49a54e705f86d51e784ebced224fdf
79945d9d 250b42a4 2067bb00 99da012e c113b49a 54e705f8 6d51e784 ebced224
fdff3f52 ca588d64 e75f6033 61bd543f d631f592 2f87ceb2 ab034149 6df84a35
$ bash install.sh
I prefer style which allows dry run mode (without | sh) :
cat a.txt | xargs -I % echo "command1; command2; ... " | sh
Works with pipes too:
cat a.txt | xargs -I % echo "echo % | cat " | sh
This is just another approach without xargs nor cat:
while read stuff; do
command1 "$stuff"
command2 "$stuff"
...
done < a.txt
This seems to be the safest version.
tr '[\n]' '[\0]' < a.txt | xargs -r0 /bin/bash -c 'command1 "$#"; command2 "$#";' ''
(-0 can be removed and the tr replaced with a redirect (or the file can be replaced with a null separated file instead). It is mainly in there since I mainly use xargs with find with -print0 output) (This might also be relevant on xargs versions without the -0 extension)
It is safe, since args will pass the parameters to the shell as an array when executing it. The shell (at least bash) would then pass them as an unaltered array to the other processes when all are obtained using ["$#"][1]
If you use ...| xargs -r0 -I{} bash -c 'f="{}"; command "$f";' '', the assignment will fail if the string contains double quotes. This is true for every variant using -i or -I. (Due to it being replaced into a string, you can always inject commands by inserting unexpected characters (like quotes, backticks or dollar signs) into the input data)
If the commands can only take one parameter at a time:
tr '[\n]' '[\0]' < a.txt | xargs -r0 -n1 /bin/bash -c 'command1 "$#"; command2 "$#";' ''
Or with somewhat less processes:
tr '[\n]' '[\0]' < a.txt | xargs -r0 /bin/bash -c 'for f in "$#"; do command1 "$f"; command2 "$f"; done;' ''
If you have GNU xargs or another with the -P extension and you want to run 32 processes in parallel, each with not more than 10 parameters for each command:
tr '[\n]' '[\0]' < a.txt | xargs -r0 -n10 -P32 /bin/bash -c 'command1 "$#"; command2 "$#";' ''
This should be robust against any special characters in the input. (If the input is null separated.) The tr version will get some invalid input if some of the lines contain newlines, but that is unavoidable with a newline separated file.
The blank first parameter for bash -c is due to this: (From the bash man page) (Thanks #clacke)
-c If the -c option is present, then commands are read from the first non-option argument com‐
mand_string. If there are arguments after the command_string, the first argument is assigned to $0
and any remaining arguments are assigned to the positional parameters. The assignment to $0 sets
the name of the shell, which is used in warning and error messages.
One thing I do is to add to .bashrc/.profile this function:
function each() {
while read line; do
for f in "$#"; do
$f $line
done
done
}
then you can do things like
... | each command1 command2 "command3 has spaces"
which is less verbose than xargs or -exec. You could also modify the function to insert the value from the read at an arbitrary location in the commands to each, if you needed that behavior also.
Another possible solution that works for me is something like -
cat a.txt | xargs bash -c 'command1 $#; command2 $#' bash
Note the 'bash' at the end - I assume it is passed as argv[0] to bash. Without it in this syntax the first parameter to each command is lost. It may be any word.
Example:
cat a.txt | xargs -n 5 bash -c 'echo -n `date +%Y%m%d-%H%M%S:` ; echo " data: " $#; echo "data again: " $#' bash
My current BKM for this is
... | xargs -n1 -I % perl -e 'system("echo 1 %"); system("echo 2 %");'
It is unfortunate that this uses perl, which is less likely to be installed than bash; but it handles more input that the accepted answer. (I welcome a ubiquitous version that does not rely on perl.)
#KeithThompson's suggestion of
... | xargs -I % sh -c 'command1; command2; ...'
is great - unless you have the shell comment character # in your input, in which case part of the first command and all of the second command will be truncated.
Hashes # can be quite common, if the input is derived from a filesystem listing, such as ls or find, and your editor creates temporary files with # in their name.
Example of the problem:
$ bash 1366 $> /bin/ls | cat
#Makefile#
#README#
Makefile
README
Oops, here is the problem:
$ bash 1367 $> ls | xargs -n1 -I % sh -i -c 'echo 1 %; echo 2 %'
1
1
1
1 Makefile
2 Makefile
1 README
2 README
Ahh, that's better:
$ bash 1368 $> ls | xargs -n1 -I % perl -e 'system("echo 1 %"); system("echo 2 %");'
1 #Makefile#
2 #Makefile#
1 #README#
2 #README#
1 Makefile
2 Makefile
1 README
2 README
$ bash 1369 $>
Try this:
git config --global alias.all '!f() { find . -d -name ".git" | sed s/\\/\.git//g | xargs -P10 -I{} git --git-dir={}/.git --work-tree={} $1; }; f'
It runs ten threads in parallel and does what ever git command you want to all repos in the folder structure. No matter if the repo is one or n levels deep.
E.g: git all pull
I have good idea to solve the problem.
Only write a comman mcmd, then you can do
find . -type f | xargs -i mcmd echo {} ## cat {} #pipe sed -n '1,3p'
The mcmd content as follows:
echo $* | sed -e 's/##/\n/g' -e 's/#pipe/|/g' | csh
I'm trying to clean up this script I have and this piece of code is annoying me because I know it can be more DRY:
if grep --version | grep "GNU" > /dev/null ;
then
grep -P -r -l "\x0d" $dir | grep "${fileRegex}"
else
grep -r -l "\x0d" $dir | grep "{$fileRegex}"
fi
My thoughts are to somehow conditionally set a string variable to either "grep -P" or "egrep" and then in a single line do something like:
$(cmdString) -r -l "\x0d" $dir | grep "${fileRegex}"
Or something like that but it doesn't work.
Are you worried about a host which has GNU grep but not egrep? Do such hosts exist?
If not why not just always use egrep? (Though -P and egrep are not the same thing.)
That being said you don't use strings for this (see BashFAQ#50).
You use arrays: grepcmd=(egrep) or grepcmd=(grep -P) and then "${grepcmd[#]}" ....
You can also avoid needing perl mode entirely if you use $'\r' or similar (assuming your shell understands that quoting method).
You can do this:
if grep --version | grep "GNU" > /dev/null
then
cmdString=(grep -P)
else
cmdString=(egrep)
fi
"${cmdString[#]}" -r -l "\x0d" "$dir" | grep "{$fileRegex}"
#Etan Reisner's suggestion worked well. For those that are interested in the final code (this case is for tabs, not windows line endings but it is similar):
fileRegex=${1:-".*\.java"}
if grep --version | grep "GNU" > /dev/null ;
then
cmdString=(grep -P)
else
cmdString=(grep)
fi
arr=$("${cmdString[#]}" -r -l "\x09" . | grep "${fileRegex}")
if [ -n "$dryRun" ]; then
for i in $arr; do echo "$i"; done
else
for i in $arr; do expand -t 7 "$i" > /tmp/e && mv /tmp/e "$i"; done
fi