Bash – Write PID To File On Bash Execution

bashbash-scriptingcron

I'm executing a bash script via cron. I want to write the process id (PID) of the script to a /tmp/ file for reference, in case I need to kill it later on (this script can take 6 – 10 hours to complete).

Is it possible to do something like this:

#!/bin/sh

echo ${PID} > /tmp/backup_pid
...
rest of the script

Each time the script executes tar or rsync, they are launched as independant processes, hence why I'd like this PID feature.

This answer (https://superuser.com/a/238533/314696) suggests using eval, but I've been taught that eval is evil. Thanks.

Best Answer

The shell variable $$ contains the PID of the current running script. You could use it like this:

echo $$ >/tmp/backup_pid

Related Solutions

Bash – Write a PID File Manually from Script

You can easily run the process in the background with "&", then get the PID of the background process using "$!"

#!/bin/bash
long_running_tool &
echo $! > pid_file

Then, optionally, wait $! if you want the shell to block until the process completes execution.

Linux – Where should I export an environment variable so that all combinations of bash/dash, interactive/non-interactive, login/non-login, will pick it up

Shell invocation is a bit of a complicated thing. The bash and dash man pages has INVOCATION sections about this.

In summary they says (there is more detail in the man page, you should read it):

When bash is                   | it reads
-------------------------------|----------
login shell                    | /etc/profile and then the first of ~/.bash_profile, ~/.bash_login or ~/.profile that exists.
                               |
interactive non-login shell    | /etc/bash.bashrc then ~/.bashrc
                               |
non-interactive shell          | The contents of $BASH_ENV (if it exists)
                               |
interactive (as "sh")          | The contents of $ENV (if it exists)

When dash is                   | it reads
-------------------------------|---------
login shell                    | /etc/profile then .profile
                               |
interactive shell              | The contents of ENV (it it exists, can be set in .profile as well as in initial environment)

I don't know about other shells offhand as I never use any of them. Your best bet might be to set a couple environment variables to point at the common location script and manually source that (when appropriate) in the couple of cases that doesn't cover.

Best Answer

Related Solutions

Bash – Write a PID File Manually from Script

Linux – Where should I export an environment variable so that all combinations of bash/dash, interactive/non-interactive, login/non-login, will pick it up

Related Question