i'd argue that env(1)'s name has mislead you --- it's most _commonly_ used just for the "do a $PATH lookup" side-effect, so a shell script only has assume that it knows where _env_ lives, without having to assume that it knows where (say) python lives. so `#!/usr/bin/env python` rather than `#!/usr/bin/python`, for example.
(similarly, it's also a useful portable-between-shells way to say "i want to call the _real_ command here, not an alias or shell builtin".) using env to set environment variables is probably most useful when used in conjunction with env's -i option to _clear_ the environment, in cases where you don't want to say "this command should _also_ have FOO=BAR in its environment", but want to say "this command should _only_ have FOO=BAR in its environment". (though not only do i anecdotally not see that very often, in the source that's easily available for me to search, it genuinely doesn't occur very often.) see also https://pubs.opengroup.org/onlinepubs/9699919799.2018edition/utilities/env.html, in particular the RATIONALE section (in particular, the very last part, about whether env(1) is actually redundant). On Thu, Jun 6, 2024 at 11:28 AM Hongyi Zhao <hongyi.z...@gmail.com> wrote: > > On Wed, Jun 5, 2024 at 5:24 PM Collin Funk <collin.fu...@gmail.com> wrote: > > > > Hi, > > > > Hongyi Zhao <hongyi.z...@gmail.com> writes: > > > > > Using env command: > > > > > > env PATH="/custom/path:$PATH" my_command > > > > > > Directly setting the environment variable: > > > > > > PATH="/custom/path:$PATH" my_command > > [...] > > > In what scenarios would it be more appropriate to use env versus > > > directly setting the environment variable? Are there specific > > > advantages or disadvantages associated with each method? > > > > One minor problem is that csh [1] doesn't use the same syntax for > > variable assignment. Up until recently FreeBSD used csh as the default > > login shell for root accounts. I doubt you will run into the problem > > anywhere else. > > > > Here is an example: > > > > $ bash > > $ env | grep '^VAR' > > $ env VAR='abc' | grep '^VAR' > > VAR=abc > > $ VAR='abc' env | grep '^VAR' > > VAR=abc > > $ csh > > % env | grep '^VAR' > > % env VAR='abc' | grep '^VAR' > > VAR=abc > > % VAR='abc' env | grep '^VAR' > > VAR=abc: Command not found. > > > > You could use: > > > > % setenv VAR 'abc' ; env | grep '^VAR' > > > > But that would set the environment variable in the parent process which > > isn't the intention. > > > > Collin > > > > [1] https://en.wikipedia.org/wiki/C_shell > > Thank you very much to everyone here for their responses to this > issue. I need to carefully read the relevant explanations and further > observe in subsequent practices to see if I have fully understood the > issue or if there are still areas that need further discussion. > > Regards, > Zhao >
