Sed for linux

[BluThaitanium]

Fixes updating licensing by running the correct sed command corresponding to Linux and MacOS
For readability- Sed commands are in separate functions, called by each xxxx_comment() function in add_license_headers.sh during execution.
Throws error statement without exit code, indicating the command isn't working due to OS limitations of sed (i.e. user is using Windows)

Resolves #249

@ckadner

[ckadner]

Thanks Phu. This is great. We need to make a few more changes though.

1. We need to exclude any *.bundle.js files. These are generated and meant to be as small as possible
2. We need different replacements for the various file types since comments in Bash scripts are different from comments in HTML or CSS. So we should instead create one alias for the sed command, i.e. call it gsed at the beginning of the script and then use that and leave the hash_comment and slash_comment, ... functions unchanged otherwise.

if [[ "$OSTYPE" == "linux-gnu"* ]]; then  # Linux
    alias gsed="sed -i"
elif [[ "$OSTYPE" == "darwin"* ]]; then  # macOS
    alias gsed="sed -i ''"
elif [[ "$OSTYPE" == "cygwin" ]]; then  # POSIX compatible emulation for Windows
    alias gsed="sed -i"
else
    echo "FAILED. OS not compatible with script '/hack/add_license_headers.sh'"
    exit 1
fi

And then use gsed in the *_comment () functions:

hash_comment () {
  echo "$1"
  if ! grep -q "SPDX-License-Identifier" "$1"
  then
    gsed '1i\
    # Copyright 2021 The MLX Contributors\
    #\
    # SPDX-License-Identifier: Apache-2.0\
    ' "$1"
  fi
}

[ckadner]

Thanks Phu just a few more changes :-)

[ckadner]

Thanks @BluThaitanium.

I just gave it a spin and came across a few issues.

[ckadner]

/lgtm

Thank you @BluThaitanium

[mlx-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: BluThaitanium, ckadner

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