Escaping characters in bash (for JSON)

Instead of worrying about how to properly quote the data, just save it to a file and use the @ construct that curl allows with the --data option. To ensure that the output of git is correctly escaped for use as a JSON value, use a tool like jq to generate the JSON, instead of creating it manually.

jq -n --arg msg "$(git log -n 1 --format=oneline | grep -o ' .\+')" \
   '{payload: { message: $msg }}' > git-tmp.txt

curl -i -X POST \
  -H 'Accept: application/text' \
  -H 'Content-type: application/json' \
  -d @git-tmp.txt \
  'https://example.com'

You can also read directly from standard input using -d @-; I leave that as an exercise for the reader to construct the pipeline that reads from git and produces the correct payload message to upload with curl.

(Hint: it's jq ... | curl ... -d@- 'https://example.com' )

Using Python:

This solution is not pure bash, but it's non-invasive and handles unicode.

json_escape () {
    printf '%s' "$1" | python -c 'import json,sys; print(json.dumps(sys.stdin.read()))'
}

Note that JSON is part of the standard python libraries and has been for a long time, so this is a pretty minimal python dependency.

Or using PHP:

json_escape () {
    printf '%s' "$1" | php -r 'echo json_encode(file_get_contents("php://stdin"));'
}

Use like so:

$ json_escape "ヤホー"
"\u30e4\u30db\u30fc"

jq can do this.

Lightweight, free, and written in C, jq enjoys widespread community support with over 15k stars on GitHub. I personally find it very speedy and useful in my daily workflow.

Convert string to JSON

$ echo -n '猫に小判' | jq -Rsa .
"\u732b\u306b\u5c0f\u5224"

To explain,

• -R means "raw input"
• -s means "include linebreaks" (mnemonic: "slurp")
• -a means "ascii output" (optional)
• . means "output the root of the JSON document"

Git + Grep Use Case

To fix the code example given by the OP, simply pipe through jq.

MSG=`git log -n 1 --format=oneline | grep -o ' .\+' | jq -Rsa .`