terraform_docs hook requires GNU sed

[brainsik]

I kept getting this error when trying to use the terraform_docs hook:

Terraform Docs...........................................................Failed
hookid: terraform_docs

sed: 1: "/BEGINNING OF PRE-COMMI ...": unexpected EOF (pending }'s)

Further inspection revealed this is a limitation of the BSD sed shipping with the latest macOS:

$ sed -i -n '/BEGINNING OF PRE-COMMIT-TERRAFORM DOCS HOOK/{p;:a;N;/END OF PRE-COMMIT-TERRAFORM DOCS HOOK/!ba;s/.*\n/I_WANT_TO_BE_REPLACED\n/};p' README.md
sed: 1: "/BEGINNING OF PRE-COMMI ...": unexpected EOF (pending }'s)

Running the same command using GNU sed (installed as gsed by Homebrew):

$ gsed -i -n '/BEGINNING OF PRE-COMMIT-TERRAFORM DOCS HOOK/{p;:a;N;/END OF PRE-COMMIT-TERRAFORM DOCS HOOK/!ba;s/.*\n/I_WANT_TO_BE_REPLACED\n/};p' README.md
$ cat README.md 
<!-- BEGINNING OF PRE-COMMIT-TERRAFORM DOCS HOOK -->
I_WANT_TO_BE_REPLACED
<!-- END OF PRE-COMMIT-TERRAFORM DOCS HOOK -->

[antonbabenko]

First, thanks for opening this issue!

The question which I have been asking myself few times in several projects which version(s) of sed should I use. If I understand correctly GNU sed is more powerful and easily available for the most of operating systems (right?).

Will it be fine, if we just extend the script to print a statement that GNU sed should be installed? "pass" if GNU sed does not exist.

It may be possible to rewrite it using Python (or anything else), but there will be the similar issue - which version of Python to expect (python 2.7 vs 3.x?)

[brainsik]

I ended up rewriting the sed commands in Perl, which should make the script more universally usable without external tools. See #15.

[varac]

Well, not excatly because it breaks setups in small docker images where perl is not installed (like the official hashicorp/terraform:0.13.5 docker image i.e.):

Terraform docs...........................................................Failed
- hook id: terraform_docs
- exit code: 127

/builds/project-0/.cache/pre-commit/repowvx2neb8/terraform_docs.sh: line 144: perl: command not found

[antonbabenko]

Make sure to install perl. I know it sounds odd in 2020 but we use it here also :)