A Terraform validation and formatting pre-commit hook

pre-commit

#!/usr/bin/env bash
set -e

# Formats any *.tf files according to the hashicorp convention
files=$(git diff --cached --name-only)
for f in $files
do
  if [ -e "$f" ] && [[ $f == *.tf ]]; then
    #terraform validate `dirname $f`
    terraform fmt $f
    git add $f
  fi
done

Add --diff-filter=d to the git diff command to filter deleted files, can't run fmt on those.

Format tfvars files [[ "${f##*.}" =~ ^(tf|tfvars)$ ]]

Format tfvars files [[ "${f##*.}" =~ ^(tf|tfvars)$ ]]

can you explain this regex?

I like to avoid magic git add as well.
Here is @eschwartz suggested version with extra error message

#!/usr/bin/env bash
set -e

# Formats any *.tf files according to the hashicorp convention
files=$(git diff --cached --name-only)
for f in $files
do
  if [ -e "$f" ] && [[ "${f##*.}" =~ ^(tf|tfvars)$ ]]; then
    terraform fmt -check=true $f || (echo "pre-hook: Please apply 'terraform fmt' for file $f before commiting or remove this file from stage" && false )
fi
done

Extending the previous ideas: avoid automatically running git add, however automatically run terraform fmt and let the user the responsibility to stage changes or not.

#!/usr/bin/env bash
set -e

# Formats any *.tf files according to the hashicorp convention
files=$(git diff --cached --name-only)
for f in $files
do
  if [ -e "$f" ] && [[ $f == *.tf ]]; then
    terraform fmt -check=true $f > /dev/null || {
        echo "pre-hook: Incorrect formatting, let me fix this for you"
        cmd="terraform fmt -recursive"
        echo "Running '$cmd'..."
        $cmd
        echo "Done. You may now stage changes."
    }
  fi
done