Use awk for reliable path stripping

[umireon]

nvm_strip_path() will fail if NVM_DIR contains meta characters such as #*.^$[]\.

$ NVM_DIR='/#'
$ echo "${NVM_DIR}/1/bin:${NVM_DIR}/2/bin:${NVM_DIR}/3/bin:/usr/bin" | sed \
  -e "s#${NVM_DIR}/[^/]*/bin[^:]*:##g" \
  -e "s#:${NVM_DIR}/[^/]*/bin[^:]*##g" \
  -e "s#${NVM_DIR}/[^/]*/bin[^:]*##g"

sed: 1: "s#/#/[^/]*/bin[^:]*:##g
": bad flag in substitute command: '#'

awk is capable to solve this problem.

$ NVM_DIR='/#*.^$[]'
$ printf %s "${NVM_DIR}/1/bin:${NVM_DIR}/2/bin:${NVM_DIR}/3/bin:/usr/bin" |
  awk -v NVM_DIR="${NVM_DIR}" -v RS=: '
  index($0, NVM_DIR) == 1 {
    path = substr($0, length(NVM_DIR) + 1)
    if (path ~ "^/[^/]*'"${2-}"'.*$") { next }
  }
  { print }' | paste -s -d: -

/usr/bin

[ljharb]

Are those characters even valid in a PATH?

[ljharb]

Can you add tests that would have failed without your change?

Also, what is paste? Is it part of POSIX?

[umireon]

Are those characters even valid in a PATH?

According to SUS, there seems to be no restriction in PATH other than :, which is the path separator, and at least they worked on my environment (macOS).

Also, what is paste? Is it part of POSIX?

paste -s -d: - is a part of POSIX.

Can you add tests that would have failed without your change?

Yes, I will.

[umireon]

A new test was added.
I also noticed that handling backslash like \+ needs an additional work to escape backslash:

awk -v NVM_DIR="$(echo ${NVM_DIR} | sed -e 's/\\/\\\\/g')" -v RS=: '

but I am not sure this should be included.

[ljharb]

If it's legal in $PATH, we might as well support it here.

[umireon]

Is this PR still valid?

[ljharb]

@umireon yep! there's an unrelated test failure; i'll rebase this again after fixing it.

[umireon]

I don't remember this PR much. I'm surprised that this PR is still valid🤣 It was 5 years ago!

[ljharb]

life comes at you fast :-p sorry it took me so long to get back to it.

[umireon]

'printf' should be command printf

[umireon]

The quotation trick is to avoid alias, the same as backslash trick.

a() {
  echo test
}

alias a=false

'a' # test

This is for functions, not for built-ins.

At that time, I misunderstood something.

[ljharb]

ah thanks, i never knew about the quotation trick, but since we use command everywhere, might as well stick to that :-)

[umireon]

For example, command nvm_has will not work so that we should do \nvm_has or 'nvm_has'.
Or not considering alias because it is prefixed by nvm_.

[ljharb]

indeed, i don't protect against that for anything that clearly belongs to nvm :-)

[umireon]

Maybe 'command' awk if you consider alias command=something🤔

[umireon]

There are too many possibilities in sourced shell scripts😭

[ljharb]

yeah true :-) if someone has aliased command everything will break, so ¯\_(ツ)_/¯

[umireon]

I learned how I use the if clause from this nvm project.
Error handling in shell scripts is so hard.

I'm not sure the awk command never fails.

[ljharb]

If tests are passing, we'll ship it, and if it fails, we'll get bug reports.

[umireon]

There are some complicated awk scripts so there seem to be practices about awk in this project, thus it's OK.

[umireon]

When I created this PR, nvm only has simple awk scripts as far as I remember, but I worry too much for now. Dismiss my comments.

[umireon]

I think awk is the best command in POSIX specification.