Edit shell script while it's running

Question

Can you edit a shell script while it's running and have the changes affect the running script?

I'm curious about the specific case of a csh script I have that batch runs a bunch of different build flavors and runs all night. If something occurs to me mid operation, I'd like to go in and add additional commands, or comment out un-executed ones.

If not possible, is there any shell or batch-mechanism that would allow me to do this?

Of course I've tried it, but it will be hours before I see if it worked or not, and I'm curious about what's happening or not happening behind the scenes.

Answer 1

Scripts don't work that way; the executing copy is independent from the source file that you are editing. Next time the script is run, it will be based on the most recently saved version of the source file.

It might be wise to break out this script into multiple files, and run them individually. This will reduce the execution time to failure. (ie, split the batch into one build flavor scripts, running each one individually to see which one is causing the trouble).

Answer 2

I'm hearing no... but what about with some indirection:

BatchRunner.sh

Command1.sh
Command2.sh

Command1.sh

runSomething

Command2.sh

runSomethingElse

Then you should be able to edit the contents of each command file before BatchRunner gets to it right?

OR

A cleaner version would have BatchRunner look to a single file where it would consecutively run one line at a time. Then you should be able to edit this second file while the first is running right?

Answer 3

If this is all in a single script, then no it will not work. However, if you set it up as a driver script calling sub-scripts, then you might be able to change a sub-script before it's called, or before it's called again if you're looping, and in that case I believe those changes would be reflected in the execution.

Answer 4

Try this... create a file called "bash-is-odd.sh":

#!/bin/bash
echo "echo yes i do odd things" >> bash-is-odd.sh

That demonstrates that bash is, indeed, interpreting the script "as you go". Indeed, editing a long-running script has unpredictable results, inserting random characters etc. Why? Because bash reads from the last byte position, so editing shifts the location of the current character being read.

Bash is, in a word, very, very unsafe because of this "feature". svn and rsync when used with bash scripts are particularly troubling, because by default they "merge" the results... editing in place. rsync has a mode that fixes this. svn and git do not.

I present a solution. Create a file called "/bin/bashx":

#!/bin/bash
source "$1"

Now use #!/bin/bashx on your scripts and always run them with "bashx" instead of bash. This fixes the issue - you can safely rsync your scripts.

Alternative (in-line) solution proposed/tested by @AF7:

{
   # your script
} 
exit $?

Curly braces protect against edits, and exit protects against appends. Of course we'd all be much better off if bash came with an option, like '-w' (whole file), or something that did this.