I have the below code to find out the number of instances of current script running that is running with same arg1. But looks like the script creates a subshell and executes this command which also shows up in output. What would be the better approach to find the number of instances of running script ?
$cat test.sh
#!/bin/bash
num_inst=`ps -ef | grep $0 | grep $1 | wc -l`
echo $num_inst
$ps aux | grep test.sh | grep arg1 | grep -v grep | wc -l
0
$./test.sh arg1 arg2
3
$
I am looking for a solution that matches all running instance of ./test.sh arg1 arg2 not the one with ./test.sh arg10 arg20
The reason this creates a subshell is that there's a pipeline inside the command substitution. If you run ps -ef alone in a command substitution, and then separately process the output from that, you can avoid this problem:
#!/bin/bash
all_processes=$(ps -ef)
num_inst=$(echo "$all_processes" | grep "$0" | grep -c "$1")
echo "$num_inst"
I also did a bit of cleanup on the script: double-quote all variable references to avoid weird parsing, used $() instead of backticks, and replaced grep ... | wc -l with grep -c.
You might also replace the echo "$all_processes" | ... with ... <<<"$all_processes" and maybe the two greps with a single grep -c "$0 $1":
...
num_inst=$(grep -c "$0 $1" <<<"$all_processes")
...
Modify your script like this:
#!/bin/bash
ps -ef | grep $0 | wc -l
No need to store the value in a variable, the result is printed to standard out anyway.
Now why do you get 3?
When you run a command within back ticks (fyi you should use syntax num_inst=$( COMMAND ) and not back ticks), it creates a new sub-shell to run COMMAND, then assigns the stdout text to the variable. So if you remove the use of $(), you will get your expected value of 2.
To convince yourself of that, remove the | wc -l, you will see that num_inst has 3 processes, not 2. The third one exists only for the execution of COMMAND.
I have a shell script, named test.sh :
#!/bin/bash
echo "start"
ps xc | grep test.sh | grep -v grep | wc -l
vartest=`ps xc | grep test.sh | grep -v grep | wc -l `
echo $vartest
echo "end"
The output result is :
start
1
2
end
So my question is, why are there two test.sh processes running when I call ps using `` (the same happens with $()) and not when I call ps directly?
How can I get the desired result (1)?
When you start a subshell, as with the backticks, bash forks itself, then executes the command you wanted to run. You then also run a pipeline which causes all of those to be run in their own subshells, so you end up with the "extra" copy of the script that's waiting for the pipeline to finish so it can gather up the output and return that to the original script.
We'll do a little expermiment using (...) to run processes explicitly in subshells and using the pgrep command which does ps | grep "name" | grep -v grep for us, just showing us the processes that match our string:
echo "Start"
(pgrep test.sh)
(pgrep test.sh) | wc -l
(pgrep test.sh | wc -l)
echo "end"
which on a run for me produces the output:
Start
30885
1
2
end
So we can see that running pgrep test.sh in a subshell only finds the single instance of test.sh, even when that subshell is part of a pipeline itself. However, if the subshell contains a pipeline then we get the forked copy of the script waiting for the pipeline to finish
I'm writing a unix shell script and need to check if there are currently running processes with "xyz" in their directory. If yes than continue to next command and show text like "Found It".
If not than don't continue and display text like "Process Not Found".
I tried something like this:
if ps -ef | grep xyz
then
echo "XYZ Process Found!"
else
echo "XYZ Process Not Found!"
fi
But it just showing me the processes and display "process found" even if there's no xyz process.
I believe you want to check the output of the command against a value using Command substition, from the linked bash-hackers wiki The command substitution expands to the output of commands. These commands are executed in a subshell, and their stdout data is what the substitution syntax expands to. Also, count the lines and remove grep. Something like,
if [[ $(ps -ef | grep xyz | grep -v grep | wc -l) != 0 ]]; then
echo "XYZ Process Found!"
else
echo "XYZ Process Not Found!"
fi
Edit
Based on the comments below, you should probably use
if [[ $(ps -ef | grep -c xyz) -ne 1 ]]; then
which is a lot easier to read.
When you run grep xyz, that process - grep xyz - is also running & thus shown in the output of ps -ef.
This running process command line contains xyz. Thus grep passes that line to output.
Hence you always get zero exit status - i.e. success.
2 Solutions:
use if ps -ef | grep '[x]yz'; then. (You may want to suppress grep output with -q)
The grep command being run is grep [x]yz. This gets printed in ps -ef output.
Obviously, grep filters out this line. [x]yz could be matched with \[x\]yz, not with [x]yz.
use if pgrep -f xyz >/dev/null; then
Check man pgrep for more details..
You can also use pgrep. From pgrep(1):
pgrep looks through the currently running processes and lists the
process IDs which match the selection criteria to stdout.
[...]
EXIT STATUS
0 One or more processes matched the criteria.
1 No processes matched.
2 Syntax error in the command line.
3 Fatal error: out of memory etc.
Example output:
[~]% pgrep xterm
18231
19070
31727
You can use it in an if statement like so:
if pgrep xterm > /dev/null; then
echo Found xterm
else
echo xterm not found
fi
Note: pgrep is not a standard utility (ie. it's not in POSIX), but widely available on at least Linux and I believe most BSD systems.
is_xyz_running() {
[ "$(pgrep xyz)" ] && echo true || echo false
}
I have an init file (/etc/profile.d/which2.sh) that aliases the which command whenever any shell starts. In bash or sh that is fine but in zsh I don't want that as which is a built-in that is already aware of aliases and functions. How can I have the script 'know' when it is under zsh and not execute the alias?
$0 does not help.
I have fixed the problem by simply unsetting the alias in zsh-specific ~/.zshrc, but I would like to know another way.
How about
[ "$(which which)" = /usr/bin/which ] && alias which "whichever"
This doesn't verify the name of the shell; rather it verifies the shell's behaviour. That's an instance of a generally-applicable programming paradigm: test behaviour directly whenever possible. (See, for example, browser detection.)
In this case, if you just checked the shell's name as a proxy for a behaviour check, you might luck out now, but things could break in the future. The name is actually arbitrary, and new names might easily be introduced. For example, in some distros ksh is a hard-link to zsh; zsh will adapt its behaviour in an attempt to emulate ksh. As another example, I have two different zsh versions, one of which is invoked as zsh5.
Ideally, the test wouldn't depend on the precise location of the which utility, either.
What are you testing for? In the old days when we had to determine whether we were running under Kornshell or Bournshell, we could do the following test:
if [ "$RANDOM" = "$RANDOM" ]
then
echo "This is the Bourne shell"
/bin/ksh $* # Script needs the Kornshell
else
echo "This is the Kornshell"
fi
Of course, both Kornshell and Bash expand $RANDOM (and so does zsh)...
Okay... You can find the processes running on the current tty this way:
ps -ft $(tty)
A little formatting:
$ ps -ocommand="" -t$(tty)
login -pf david
-ksh
bash
Pretty good. Shells end with sh, so I'll make that assumption. I just want the lines ending with sh:
$ ps -ocommand="" -t$(tty) | grep "sh$"
-ksh
bash
Yes, I'm running two shells in this TTY. I login with the Kornshell, and shelled out to bash. Let's toss the PID in the mix:
$ ps -t$(tty) -opid="" -ocommand="" | grep "sh$"
62599 -ksh
62855 bash
We want the one with the highest PID
$ ps -t$(tty) -opid="" -ocommand="" | grep "sh$" | sort -k1,1nr | head -1
62983 bash
Yup, I'm running Bash. Let's get rid of the PID:
$ ps -t$(tty) -opid="" -ocommand="" | grep "sh$" | sort -k1,1nr | head -1 | sed 's/.* //'
bash
Let's see if it works with various shells:
$ ps -t$(tty) -opid="" -ocommand="" | grep "sh$" | sort -k1,1nr | head -1 | sed 's/.* //'
ksh
Kornshell is fine.
$ ps -t$(tty) -opid="" -ocommand="" | grep "sh$" | sort -k1,1nr | head -1 | sed 's/.* //'
zsh
Works with zsh
$ ps -t$(tty) -opid="" -ocommand="" | grep "sh$" | sort -k1,1nr | head -1 | sed 's/.* //'
sh
Works with Dash or Ash
% ps -t$(tty) -opid="" -ocommand="" | grep "sh$" | sort -k1,1nr | head -1 | sed 's/.* //'
Illegal variable name.
Doesn't work in tcsh. Oh well... You can't please everybody.
#rici's approach is the most robust and generic solution.
A simpler, zsh-specific approach would be to use:
# Define a `which` alias only when NOT run by `zsh`.
[ -z $ZSH_VERSION ] && alias which ...
Some background information on how to determine the specific shell [binary] that is currently executing:
A robust option is to call the ps utility, relying on the fact POSIX-like shells as well as csh / tcsh report their own PID (process ID) via built-in variable $$:
ps -p $$ -o "comm="
Note: ps implementations differ with respect to what path form they report; e.g.:
macOS reports the binary path as invoked, which may be the mere file name, the full path, or even a relative path; additionally, if the shell was invoked as a login shell, such as via sudo -i, the mere file name can be prefixed with - (e.g., -bash).
by contrast, the procps-ng 3.3.12 ps implementation that comes with Ubuntu 18.04 only ever reports the file name, and never with the - prefix.
Alternatively, for scripts that are being sourced, as initialization files are, as well as interactive shells, you can examine the value of $0; note, however, that this is not foolproof, because the caller may have set $0 to an arbitrary value.
It points to the shell binary as invoked, i.e., the value may be either a mere filename or a path.
The value may be prefixed with -, namely if the shell is a login shell; e.g., -bash in a shell started with sudo -i.
Note: Do NOT use $SHELL, as it only ever reflects the current user's default shell. Its value doesn't change even when running other shells later.
Thus, a POSIX-compatible way of obtaining the current shell's executable filename is:
basename -- "${0#-}" # -> (e.g., in bash) 'bash'; will NOT work in csh/tcsh
Examples:
currShell=$(basename -- "${0#-}") # Store shell-binary filename in variable.
[ "$(basename -- "${0#-}")" = 'zsh' ] && echo "This is a ZSH shell."
If it is sufficient to test for a specific shell only, you may be able to simply test for the presence of specific environment variables such as $BASH_VERSION, $ZSH_VERSION, or $KSH_VERSION.
Note, however, that not all shells have such characteristic variables; dash, for instance, does not.
Example:
[ -n "$ZSH_VERSION" ] && echo "This is a ZSH shell."
The SHELL environment variable contains the full path to the binary of your shell. You could use that (or its basename):
s=$(basename $SHELL)
[ "$s" = 'zsh' ] || alias which="what you want it to be"
How can I determine the current shell I am working on?
Would the output of the ps command alone be sufficient?
How can this be done in different flavors of Unix?
There are three approaches to finding the name of the current shell's executable:
Please note that all three approaches can be fooled if the executable of the shell is /bin/sh, but it's really a renamed bash, for example (which frequently happens).
Thus your second question of whether ps output will do is answered with "not always".
echo $0 - will print the program name... which in the case of the shell is the actual shell.
ps -ef | grep $$ | grep -v grep - this will look for the current process ID in the list of running processes. Since the current process is the shell, it will be included.
This is not 100% reliable, as you might have other processes whose ps listing includes the same number as shell's process ID, especially if that ID is a small number (for example, if the shell's PID is "5", you may find processes called "java5" or "perl5" in the same grep output!). This is the second problem with the "ps" approach, on top of not being able to rely on the shell name.
echo $SHELL - The path to the current shell is stored as the SHELL variable for any shell. The caveat for this one is that if you launch a shell explicitly as a subprocess (for example, it's not your login shell), you will get your login shell's value instead. If that's a possibility, use the ps or $0 approach.
If, however, the executable doesn't match your actual shell (e.g. /bin/sh is actually bash or ksh), you need heuristics. Here are some environmental variables specific to various shells:
$version is set on tcsh
$BASH is set on bash
$shell (lowercase) is set to actual shell name in csh or tcsh
$ZSH_NAME is set on zsh
ksh has $PS3 and $PS4 set, whereas the normal Bourne shell (sh) only has $PS1 and $PS2 set. This generally seems like the hardest to distinguish - the only difference in the entire set of environment variables between sh and ksh we have installed on Solaris boxen is $ERRNO, $FCEDIT, $LINENO, $PPID, $PS3, $PS4, $RANDOM, $SECONDS, and $TMOUT.
ps -p $$
should work anywhere that the solutions involving ps -ef and grep do (on any Unix variant which supports POSIX options for ps) and will not suffer from the false positives introduced by grepping for a sequence of digits which may appear elsewhere.
Try
ps -p $$ -oargs=
or
ps -p $$ -ocomm=
If you just want to ensure the user is invoking a script with Bash:
if [ -z "$BASH" ]; then echo "Please run this script $0 with bash"; exit; fi
or ref
if [ -z "$BASH" ]; then exec bash $0 ; exit; fi
You can try:
ps | grep `echo $$` | awk '{ print $4 }'
Or:
echo $SHELL
$SHELL need not always show the current shell. It only reflects the default shell to be invoked.
To test the above, say bash is the default shell, try echo $SHELL, and then in the same terminal, get into some other shell (KornShell (ksh) for example) and try $SHELL. You will see the result as bash in both cases.
To get the name of the current shell, Use cat /proc/$$/cmdline. And the path to the shell executable by readlink /proc/$$/exe.
There are many ways to find out the shell and its corresponding version. Here are few which worked for me.
Straightforward
$> echo $0 (Gives you the program name. In my case the output was -bash.)
$> $SHELL (This takes you into the shell and in the prompt you get the shell name and version. In my case bash3.2$.)
$> echo $SHELL (This will give you executable path. In my case /bin/bash.)
$> $SHELL --version (This will give complete info about the shell software with license type)
Hackish approach
$> ******* (Type a set of random characters and in the output you will get the shell name. In my case -bash: chapter2-a-sample-isomorphic-app: command not found)
ps is the most reliable method. The SHELL environment variable is not guaranteed to be set and even if it is, it can be easily spoofed.
I have a simple trick to find the current shell. Just type a random string (which is not a command). It will fail and return a "not found" error, but at start of the line it will say which shell it is:
ksh: aaaaa: not found [No such file or directory]
bash: aaaaa: command not found
I have tried many different approaches and the best one for me is:
ps -p $$
It also works under Cygwin and cannot produce false positives as PID grepping. With some cleaning, it outputs just an executable name (under Cygwin with path):
ps -p $$ | tail -1 | awk '{print $NF}'
You can create a function so you don't have to memorize it:
# Print currently active shell
shell () {
ps -p $$ | tail -1 | awk '{print $NF}'
}
...and then just execute shell.
It was tested under Debian and Cygwin.
The following will always give the actual shell used - it gets the name of the actual executable and not the shell name (i.e. ksh93 instead of ksh, etc.). For /bin/sh, it will show the actual shell used, i.e. dash.
ls -l /proc/$$/exe | sed 's%.*/%%'
I know that there are many who say the ls output should never be processed, but what is the probability you'll have a shell you are using that is named with special characters or placed in a directory named with special characters? If this is still the case, there are plenty of other examples of doing it differently.
As pointed out by Toby Speight, this would be a more proper and cleaner way of achieving the same:
basename $(readlink /proc/$$/exe)
My variant on printing the parent process:
ps -p $$ | awk '$1 == PP {print $4}' PP=$$
Don't run unnecessary applications when AWK can do it for you.
Provided that your /bin/sh supports the POSIX standard and your system has the lsof command installed - a possible alternative to lsof could in this case be pid2path - you can also use (or adapt) the following script that prints full paths:
#!/bin/sh
# cat /usr/local/bin/cursh
set -eu
pid="$$"
set -- sh bash zsh ksh ash dash csh tcsh pdksh mksh fish psh rc scsh bournesh wish Wish login
unset echo env sed ps lsof awk getconf
# getconf _POSIX_VERSION # reliable test for availability of POSIX system?
PATH="`PATH=/usr/bin:/bin:/usr/sbin:/sbin getconf PATH`"
[ $? -ne 0 ] && { echo "'getconf PATH' failed"; exit 1; }
export PATH
cmd="lsof"
env -i PATH="${PATH}" type "$cmd" 1>/dev/null 2>&1 || { echo "$cmd not found"; exit 1; }
awkstr="`echo "$#" | sed 's/\([^ ]\{1,\}\)/|\/\1/g; s/ /$/g' | sed 's/^|//; s/$/$/'`"
ppid="`env -i PATH="${PATH}" ps -p $pid -o ppid=`"
[ "${ppid}"X = ""X ] && { echo "no ppid found"; exit 1; }
lsofstr="`lsof -p $ppid`" ||
{ printf "%s\n" "lsof failed" "try: sudo lsof -p \`ps -p \$\$ -o ppid=\`"; exit 1; }
printf "%s\n" "${lsofstr}" |
LC_ALL=C awk -v var="${awkstr}" '$NF ~ var {print $NF}'
My solution:
ps -o command | grep -v -e "\<ps\>" -e grep -e tail | tail -1
This should be portable across different platforms and shells. It uses ps like other solutions, but it doesn't rely on sed or awk and filters out junk from piping and ps itself so that the shell should always be the last entry. This way we don't need to rely on non-portable PID variables or picking out the right lines and columns.
I've tested on Debian and macOS with Bash, Z shell (zsh), and fish (which doesn't work with most of these solutions without changing the expression specifically for fish, because it uses a different PID variable).
If you just want to check that you are running (a particular version of) Bash, the best way to do so is to use the $BASH_VERSINFO array variable. As a (read-only) array variable it cannot be set in the environment,
so you can be sure it is coming (if at all) from the current shell.
However, since Bash has a different behavior when invoked as sh, you do also need to check the $BASH environment variable ends with /bash.
In a script I wrote that uses function names with - (not underscore), and depends on associative arrays (added in Bash 4), I have the following sanity check (with helpful user error message):
case `eval 'echo $BASH#${BASH_VERSINFO[0]}' 2>/dev/null` in
*/bash#[456789])
# Claims bash version 4+, check for func-names and associative arrays
if ! eval "declare -A _ARRAY && func-name() { :; }" 2>/dev/null; then
echo >&2 "bash $BASH_VERSION is not supported (not really bash?)"
exit 1
fi
;;
*/bash#[123])
echo >&2 "bash $BASH_VERSION is not supported (version 4+ required)"
exit 1
;;
*)
echo >&2 "This script requires BASH (version 4+) - not regular sh"
echo >&2 "Re-run as \"bash $CMD\" for proper operation"
exit 1
;;
esac
You could omit the somewhat paranoid functional check for features in the first case, and just assume that future Bash versions would be compatible.
None of the answers worked with fish shell (it doesn't have the variables $$ or $0).
This works for me (tested on sh, bash, fish, ksh, csh, true, tcsh, and zsh; openSUSE 13.2):
ps | tail -n 4 | sed -E '2,$d;s/.* (.*)/\1/'
This command outputs a string like bash. Here I'm only using ps, tail, and sed (without GNU extesions; try to add --posix to check it). They are all standard POSIX commands. I'm sure tail can be removed, but my sed fu is not strong enough to do this.
It seems to me, that this solution is not very portable as it doesn't work on OS X. :(
echo $$ # Gives the Parent Process ID
ps -ef | grep $$ | awk '{print $8}' # Use the PID to see what the process is.
From How do you know what your current shell is?.
This is not a very clean solution, but it does what you want.
# MUST BE SOURCED..
getshell() {
local shell="`ps -p $$ | tail -1 | awk '{print $4}'`"
shells_array=(
# It is important that the shells are listed in descending order of their name length.
pdksh
bash dash mksh
zsh ksh
sh
)
local suited=false
for i in ${shells_array[*]}; do
if ! [ -z `printf $shell | grep $i` ] && ! $suited; then
shell=$i
suited=true
fi
done
echo $shell
}
getshell
Now you can use $(getshell) --version.
This works, though, only on KornShell-like shells (ksh).
Do the following to know whether your shell is using Dash/Bash.
ls –la /bin/sh:
if the result is /bin/sh -> /bin/bash ==> Then your shell is using Bash.
if the result is /bin/sh ->/bin/dash ==> Then your shell is using Dash.
If you want to change from Bash to Dash or vice-versa, use the below code:
ln -s /bin/bash /bin/sh (change shell to Bash)
Note: If the above command results in a error saying, /bin/sh already exists, remove the /bin/sh and try again.
I like Nahuel Fouilleul's solution particularly, but I had to run the following variant of it on Ubuntu 18.04 (Bionic Beaver) with the built-in Bash shell:
bash -c 'shellPID=$$; ps -ocomm= -q $shellPID'
Without the temporary variable shellPID, e.g. the following:
bash -c 'ps -ocomm= -q $$'
Would just output ps for me. Maybe you aren't all using non-interactive mode, and that makes a difference.
Get it with the $SHELL environment variable. A simple sed could remove the path:
echo $SHELL | sed -E 's/^.*\/([aA-zZ]+$)/\1/g'
Output:
bash
It was tested on macOS, Ubuntu, and CentOS.
On Mac OS X (and FreeBSD):
ps -p $$ -axco command | sed -n '$p'
Grepping PID from the output of "ps" is not needed, because you can read the respective command line for any PID from the /proc directory structure:
echo $(cat /proc/$$/cmdline)
However, that might not be any better than just simply:
echo $0
About running an actually different shell than the name indicates, one idea is to request the version from the shell using the name you got previously:
<some_shell> --version
sh seems to fail with exit code 2 while others give something useful (but I am not able to verify all since I don't have them):
$ sh --version
sh: 0: Illegal option --
echo $?
2
One way is:
ps -p $$ -o exe=
which is IMO better than using -o args or -o comm as suggested in another answer (these may use, e.g., some symbolic link like when /bin/sh points to some specific shell as Dash or Bash).
The above returns the path of the executable, but beware that due to /usr-merge, one might need to check for multiple paths (e.g., /bin/bash and /usr/bin/bash).
Also note that the above is not fully POSIX-compatible (POSIX ps doesn't have exe).
Kindly use the below command:
ps -p $$ | tail -1 | awk '{print $4}'
This one works well on Red Hat Linux (RHEL), macOS, BSD and some AIXes:
ps -T $$ | awk 'NR==2{print $NF}'
alternatively, the following one should also work if pstree is available,
pstree | egrep $$ | awk 'NR==2{print $NF}'
You can use echo $SHELL|sed "s/\/bin\///g"
And I came up with this:
sed 's/.*SHELL=//; s/[[:upper:]].*//' /proc/$$/environ