Re: [PLUG] Running commands: was: Sys76

[JP Vossen via plug <plug@lists.phillylinux.org>]

On 11/24/21 4:08 PM, Steve Litt via plug wrote:
> jeffv via plug said on Wed, 24 Nov 2021 12:40:03 -0500
> > How To Run A Command After The Previous One Has Finished On Linux
> > https://www.linuxuprising.com/2021/11/how-to-run-command-after-previous-one.html
> > Using this, you can run not just 2 commands, but any number of
> > commands, after the previous one has finished. This will work with Sh,
> > Bash, Zsh and other shells.
>
> Thank you jeffv! I've been looking for this capability for years. Until
> now, when I ran more than one command after the and or or, I put those
> commands to be run after the and or or in a subroutine, which was extra
> work. Now, for just a couple commands, I'll just use the braces.

`{ }` simply denote code blocks, while `( )` spawns a sub-shell.  They are different, and that can mess you up because while the sub-shell inherits variables from the parent it can't pass them back and any changes in the sub-shell are lost!

Use `[[ expression ]] && block` or `[[ expression ]] || block` when simple and readable. Do not use `[[ expression ]] && block || block` because that doesn't do what you think it does, use `if .. then .. (elif ..) else.. fi` for that.

The `&&` and `||` operators are of *equal* precedence and are left associative.  Prove it:
	$ echo 1 && echo 2 || echo 3
	$ echo 1 || echo 2 && echo 3

Related, the examples for the forthcoming (2022-04) _bash Idioms_ are up at https://github.com/vossenjp/bashidioms-examples, in particular https://github.com/vossenjp/bashidioms-examples/blob/main/appa/bash_idioms_style_guide.md.  :-)

Later,
JP
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