Why the following if statement succeeds ?
if $(ps aux | grep -q "bla bla") ; then echo "found" ; fi
Because the grep process itself is being returned by ps. You can "trick" grep to not match itself by surrounding one of the search characters in a character class [ ] which doesn't change the functionality:
Just do:
if ps aux | grep -q "[b]la bla" ; then echo "found" ; fi
Also, the use of process substitution $() is unnecessary. The if will work on the success of the last command in the pipe chain, which is what you want.
Note: The reason the character class trick works is because the ps output still has the character class brackets but when grep is processing the search string, it uses the brackets as syntax rather than a fixed string to match.
If you grep the output from ps aux, you will always get a process showing your previous command. To fix this, you can pipe the output to grep twice, once to remove line with "grep" in it, and again for the process your looking for.
ps aux | grep -v "grep" | grep "Finder"
the 'grep' process is already running by the time ps runs, so the ps output includes it.
Try using pgrep instead.
pgrep is precisely for this purpose:
if pgrep "bla bla" ; then echo "found" ; fi
The $( is a small little bit relevant, and changes the meaning a bit. Although in this case, because there is never any output from grep -q, you can just about get away with the $(. You probably want to start with something like (as pointed out by others):
if ps aux | grep -v 'grep' | grep -q 'bla bla'; then
echo 'Found'
fi
Anyway, you started with
if $(ps aux | grep -q "bla bla") ; then echo "found" ; fi
With $(, the command inside the $( ) is executed and the output of that command is used as the command line for the outer command. Do these four experiments:
# if $(echo nonexistant ; true) ; then echo "found" ; fi
nonexistant: command not found
# if $(echo nonexistant ; false) ; then echo "found" ; fi
nonexistant: command not found
# if $(echo ; true) ; then echo "found" ; fi
found
# if $(echo ; false) ; then echo "found" ; fi
So, according to this you will output get found if both these conditions hold:
The command inside the $( ) created no output
and the command was succesful
This suggests that ps aux | grep -q "bla bla" was successful and created no output. It's no surprise that grep -q creates no output. That's what the -q is for. So therefore, your command must have had a true status, which implies that the grep did successfully find a match. We know that grep will always find a match in this case, because the list of processes from ps will include grep itself; the grep will always find itself.
You need to filter out the process that is grepping for 'bla bla':
$ if ps aux | grep -v 'grep' | grep -q 'bla bla'; then
echo 'Found'
fi
Related
into a bash script, I need to grep a contiuous log streaming and when the proper string is filtered, I need to stop the 'tailf' command to move ond with other implementations.
The common command that works is:
tailf /dir/dir/dir/server.log | grep --line-buffered "Started in"
after the "Started in" line is gathered, I need to break down the "tailf" command.
All this stuff into a bash script.
use grep -m1, it means return the first match then stop:
-m num, --max-count=num
Stop reading the file after num matches.
tailf /dir/dir/dir/server.log | grep -m1 "Started in"
Figured out...
tailf /dir/dir/dir/server.log | while read line
do
echo $line | grep "thing_to_grep"
if [ "$?" -eq "0" ]; then
echo "";echo "[ message ]";echo "";
kill -2 -$$
fi
done
$$ is the PID of the current shell, in this case associated to the "tailf" command.
for d in */ ; do
cd $d
NUM = $(echo ${PWD##*/} | grep -q "*abc*");
if [[ "$NUM" -ne "0" ]]; then
pwd
fi
cd ..
done
Here I'm trying to match a folder name to some substring 'abc' in the name of the folder and check if the output of the grep is not 0. But it gives me an error which reads that NUM: command not found
An error was addressed in comments.
NUM = $(echo ${PWD##*/} | grep -q "*abc*"); should be NUM=$(echo ${PWD##*/} | grep -q "*abc*");.
To clarify, the core problem would be to be able to match current directory name to a pattern.
You can probably simply the code to just
if grep -q "*abc*" <<< "${PWD##*/}" 2>/dev/null; then
echo "$PWD"
# Your rest of the code goes here
fi
You can use the exit code of the grep directly in a if-conditional without using a temporary variable here ($NUM here). The condition will pass if grep was able to find a match. The here-string <<<, will pass the input to grep similar to echo with a pipeline. The part 2>/dev/null is to just suppress any errors (stderr - file descriptor 2) if grep throws!
As an additional requirement asked by OP, to negate the conditional check just do
if ! grep -q "*abc*" <<< "${PWD##*/}" 2>/dev/null; then
I am trying to check the output of a command and run different commands depending on the output.
count="1"
for f in "$#"; do
BASE=${f%.*}
# if [ -e "${BASE}_${suffix}_${suffix2}.mp4" ]; then
echo -e "Reading GPS metadata using MediaInfo file ${count}/${##} "$(basename "${BASE}_${suffix}_${suffix2}.mp4")"
mediainfo "${BASE}_${suffix}_${suffix2}.mp4" | grep "©xyz" | head -n 1
if [[ $? != *xyz* ]]; then
echo -e "WARNING!!! No GPS information found! File ${count}/${##} "$(basename "${BASE}_${suffix}_${suffix2}.mp4")" || exit 1
fi
((count++))
done
MediaInfo is the command I am checking the output of.
If a video file has "©xyz" atom written into it the output looks like this:
$ mediainfo FILE | grep "©xyz" | head -n 1
$ ©xyz : +60.9613-125.9309/
$
otherwise it is null
$ mediainfo FILE | grep "©xyz" | head -n 1
$
The above code does not work and echos the warning even when ©xyz presented.
Any ideas of what I am doing wrong?
The syntax you are using the capture the output of the mediainfo command is plain wrong. When using grep you can use its return code (the output of $?) directly in the if-conditional
if mediainfo "${BASE}_${suffix}_${suffix2}.mp4" | grep -q "©xyz" 2> /dev/null;
then
..
The -q flag in grep instructs it to run the command silently without throwing any results to stdout, and the part 2>/dev/null suppresses any errors thrown via stderr, so you will get the if-conditional pass when the string is present and fail if not present
$? is the exit code of the command: a number between 0 and 255. It's not related to stdout, where your value "xyz" is written.
To match in stdout, you can just use grep:
if mediainfo "${BASE}_${suffix}_${suffix2}.mp4" | grep -q "©xyz"
then
echo "It contained that thing"
else
echo "It did not"
fi
I have a file with many service names, some of them are running, some of them aren't.
foo.service
bar.service
baz.service
I would like to find an efficient way to get the PIDs of the running processes started by the services (for the not running ones a 0, -1 or empty results are valid).
Desired output example:
foo.service:8484
bar.server:
baz.service:9447
(bar.service isn't running).
So far I've managed to do the following: (1)
cat t.txt | xargs -I {} systemctl status {} | grep 'Main PID' \
| awk '{print $3}'
With the following output:
8484
9447
But I can't tell which service every PID belongs to.
(I'm not bound to use xargs, grep or awk.. just looking for the most efficient way).
So far I've managed to do the following: (2)
for f in `cat t.txt`; do
v=`systemctl status $f | grep 'Main PID:'`;
echo "$f:`echo $v | awk '{print \$3}'`";
done;
-- this gives me my desired result. Is it efficient enough?
I ran into similar problem and fount leaner solution:
systemctl show --property MainPID --value $SERVICE
returns just the PID of the service, so your example can be simplified down to
for f in `cat t.txt`; do
echo "$f:`systemctl show --property MainPID --value $f`";
done
You could also do:
while read -r line; do
statuspid="$(sudo service $line status | grep -oP '(?<=(process|pid)\s)[0-9]+')"
appendline=""
[[ -z $statuspid ]] && appendline="${line}:${statuspid}" || appendline="$line"
"$appendline" >> services-pids.txt
done < services.txt
To use within a variable, you could also have an associative array:
declare -A servicearray=()
while read -r line; do
statuspid="$(sudo service $line status | grep -oP '(?<=(process|pid)\s)[0-9]+')"
[[ -z $statuspid ]] && servicearray[$line]="statuspid"
done < services.txt
# Echo output of array to command line
for i in "${!servicearray[#]}"; do # Iterating over the keys of the associative array
# Note key-value syntax
echo "service: $i | pid: ${servicearray[$i]}"
done
Making it more efficient:
To list all processes with their execution commands and PIDs. This may give us more than one PID per command, which might be useful:
ps -eo pid,comm
So:
psidcommand=$(ps -eo pid,comm)
while read -r line; do
# Get all PIDs with the $line prefixed
statuspids=$(echo $psidcommand | grep -oP '[0-9]+(?=\s$line)')
# Note that ${statuspids// /,} replaces space with commas
[[ -z $statuspids ]] && appendline="${line}:${statuspids// /,}" || appendline="$line"
"$appendline" >> services-pids.txt
done < services.txt
OUTPUT:
kworker:5,23,28,33,198,405,513,1247,21171,22004,23749,24055
If you're confident your file has the full name of the process, you can replace the:
grep -oP '[0-9]+(?=\s$line)'
with
grep -oP '[0-9]+(?=\s$line)$' # Note the extra "$" at the end of the regex
to make sure it's an exact match (in the grep without trailing $, line "mys" would match with "mysql"; in the grep with trailing $, it would not, and would only match "mysql").
Building up on Yorik.sar's answer, you first want to get the MainPID of a server like so:
for SERVICE in ...<service names>...
do
MAIN_PID=`systemctl show --property MainPID --value $SERVICE`
if test ${MAIN_PID} != 0
than
ALL_PIDS=`pgrep -g $MAIN_PID`
...
fi
done
So using systemctl gives you the PID of the main process controlled by your daemon. Then the pgrep gives you the daemon and a list of all the PIDs of the processes that daemon started.
Note: if the processes are user processes, you have to use the --user on the systemctl command line for things to work:
MAIN_PID=`systemctl --user show --property MainPID --value $SERVICE`
Now you have the data you are interested in the MAIN_PID and ALL_PIDS variables, so you can print the results like so:
if test -n "${ALL_PID}"
then
echo "${SERVICE}: ${ALL_PIDS}"
fi
I want to check if my VPN is connected to a specific country. The VPN client has a status option but sometimes it doesn't return the correct country, so I wrote a script to check if I'm for instance connected to Sweden. My script looks like this:
#!/bin/bash
country=Sweden
service=expressvpn
while true; do
if ((curl -s https://www.iplocation.net/find-ip-address | grep $country | grep -v "grep" | wc -l) > 0 )
then
echo "$service connected!!!"
else
echo "$service not connected!"
$service connect $country
fi;
sleep 5;
done
The problem is, it always says "service connected", even when it isn't. When I enter the curl command manually, wc -l returns 0 if it didn't find Sweden and 1 when it does. What's wrong with the if statement?
Thank you
Peter
(( )) enters a math context -- anything inside it is interpreted as a mathematical expression. (You want your code to be interpreted as a math expression -- otherwise, > 0 would be creating a file named 0 and storing wc -l's output in that file, not comparing the output of wc -l to 0).
Since you aren't using )) on the closing side, this is presumably exactly what's happening: You're storing the output of wc -l in a file named 0, and then using its exit status (successful, since it didn't fail) to decide to follow the truthy branch of the if statement. [Just adding more parens on the closing side won't fix this, either, since curl -s ... isn't valid math syntax].
Now, if you want to go the math approach, what you can do is run a command substitution, which replaces the command with its output; that is a math expression:
# smallest possible change that works -- but don't do this; see other sections
if (( $(curl -s https://www.iplocation.net/find-ip-address | grep $country | grep -v "grep" | wc -l) > 0 )); then
...if your curl | grep | grep | wc becomes 5, then after the command substitution this looks like:
if (( 5 > 0 )); then
...and that does what you'd expect.
That said, this is silly. You want to know if your target country is in curl's output? Just check for that directly with shell builtins alone:
if [[ $(curl -s https://www.iplocation.net/find-ip-address) = *"$country"* ]]; then
echo "Found $country in output of curl" >&2
fi
...or, if you really want to use grep, use grep -q (which suppresses output), and check its exit status (which is zero, and thus truthy, if and only if it successfully found a match):
if curl -s https://www.iplocation.net/find-ip-address | grep -q -e "$country"; then
echo "Found $country in output of curl with grep" >&2
fi
This is more efficient in part because grep -q can stop as soon as it finds a match -- it doesn't need to keep reading more content -- so if your file is 16KB long and the country name is in the first 1KB of output, then grep can stop reading from curl (and curl can stop downloading) as soon as that first match 1KB in is seen.
The result of the curl -s https://www.iplocation.net/find-ip-address | grep $country | grep -v "grep" | wc -l statement is text. You compare text and number, that is why your if statement does not work.
This might solve your problem;
if [ $(curl -s https://www.iplocation.net/find-ip-address | grep $country | grep -v "grep" | wc -l) == "0" ] then ...
That worked, thank you for your help, this is what my script looks now:
#!/bin/bash
country=Switzerland
service=expressvpn
while true; do
if curl -s https://www.iplocation.net/find-ip-address | grep -q -e "$country"; then
echo "Found $country in output of curl with grep" >&2
echo "$service not connected!!!"
$service connect Russia
else
echo "$service connected!"
fi;
sleep 5;
done