use builtin "command -v" instead of which

[wasnio]

We shouldn't use which because it is not built-in.

[karbassi]

I agree.

@inkarkat thoughts?

[inkarkat]

The program also uses grep, sed and awk, which also aren't built-in (but arguably much harder to implement in Bash). Of course, fewer dependencies are always desirable, but is there actually a distribution where which isn't available by default?

Unfortunately, the command -v replacement isn't 100% compatible; it accepts any callable executable, function, and even aliases. But as $PAGER is invoked inside double quotes (and it has to, as the environment variable may contain a filespec with special characters), aliases don't expand there. So if one mistakenly sets PAGER to an alias, the program would attempt to invoke it. (On the other hand, currently one could assign a function to PAGER and it would be ignored, which also is not fully correct.)

[rico-chet]

I remember stumbling upon situations where which wasn't available, but I guess this was on embedded targets or some stripped-down containers only.

The command -v replacement is superior, in my opinion, since it allows for more flexibility, e.g. by using exported functions which can be handy when creating test doubles. Aliases and functions aren't inherited per default, so if anyone wants to use a function in PAGER, she will need to export it and failing to do so is a mistake anyway.