Execute a bash script the first time shell opens - bash

Question

Is there a way to execute a bash script automatically on a daily basis, that is I want the bash script to be executed every day the first time I open a shell terminal?
Thanks!

Answer 1

Bash has two files, from the user perspective, that perform "setup" when it is launched:
.bash_profile - This file is executed whenever you open an interactive login shell. This file may also be named .profile in certain distributions or configurations. .profile is usually used for non-Bash specific configuration items. Also be aware that if you have the little used .bash_login, .bash_profile will prevent that file from being used, though it is otherwise equivalent. .bash_profile is standard.
.bashrc - This file is executed for all other bash instances. Note that it is common for people to call .bashrc from .bash_profile to create consistency.
A login shell is spawned when you login; via ssh, telnet, at a console, etc. You can also force the launch of a login shell (forcing .bash_profile) to be processed by starting a shell under su like so:
su - username
Here, the dash indicates that this should be processed as a login shell.
Neither of these seem to be the correct answer for your question, however, unless you are certain to login once each day and only once each day.
A better approach in your case would be to use the cron. Crontab allows you to schedule jobs to run at any desired interval. For daily execution, you would likely want a line configured like so:
0 5 * * * /home/user/script
This would cause the user's script to execute at 5am every day. The columns are:
0 5 * * *
^ ^ ^ ^ ^------ Day of week
^ ^ ^ ^-------- Month of year
^ ^ ^---------- Day of month
^ ^------------ Hour of day
^-------------- Minute of hour
Each of those fields can also represent a comma separated list or even an arithmetic expression. For example, the following will execute the script four times during the 5 AM hour:
*/4 5 * * *

Answer 2

If you want the script to run when you open the shell terminal only, add it to your ~/.bashrc, /etc/bash.bashrc or /etc/bashrc file. This will execute anytime an interactive non login shell is started.
If you want it to execute daily, create a cron for it in /etc/crontab or crontab -e

Answer 3

While informative, the provided answers don't actually solve for the original requirement.
The request is for a script to be run once a day, at the first login, and not again the rest of the day, but then again upon the first login the next day, and the next, etc...
To achieve this you can place the script you want to execute in ~/bin or whatever location you want it in.
At the bottom of your script.sh add these three lines which will remove the execution of the script upon subsequent logins.
cat ~/.bash_profile | grep -v script.sh > bash_profile.tmp
rm -f ~/.bash_profile
mv bash_profile.tmp ~/.bash_profile
What these three lines do:
Reads in your .bash_profile and writes everything EXCEPT the line that contains script.sh to a tmp file
Deletes the existing bash profile that contains the execution of your script
Renames the tmp file, without the script.sh line, to be your new .bash_profile on subsequent logins.
THEN, use 'crontab -e' to add a line to the crontab, that will put back that line to your .bash_profile every morning at a time you would deem to be after your last login of the day but before your first login of the day.
This example is set for zero minutes + four hours, or 4:00am.
0 4 * * * echo "~/bin/script.sh" >> ~/.bash_profile
A problem exists with this, however.
If, for example, the user only logs into the system M-F and not on Sat or Sun. The crontab will still add the line to the profile Sat and Sun morning, meaning that come Monday morning there will be three identical lines. This will cause the script to run three times.
To mitigate this, an IF statement is wrapped around it to check if the command already exists in the file before adding it.
0 4 * * * if [ "$(grep -c '~/bin/script.sh' ~/.bash_profile)" -eq 0 ]; then echo "~/bin/script.sh" >> ~/.bash_profile ; fi
The end result is:
Your script will execute upon first login of the day
At the end, your script will remove the trigger for it to execute on login
Your script will not execute on subsequent logins
Every morning, crontab will add the trigger back to your .bash_profile for it to be executed on the next login, which would be the first login that day.
But crontab will only add the trigger if it doesn't already exist.
note: This is likely not the most efficient or eloquent solution, but it does work, and is pretty simple to understand.