Escaping characters in bash (for JSON)

Question

I'm using git, then posting the commit message and other bits as a JSON payload to a server.

Currently I have:

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

which sets MSG to something like:

Calendar can't go back past today 

then

curl -i -X POST \   -H 'Accept: application/text' \   -H 'Content-type: application/json' \   -d "{'payload': {'message': '$MSG'}}" \   'https://example.com' 

My real JSON has another couple of fields.

This works fine, but of course when I have a commit message such as the one above with an apostrophe in it, the JSON is invalid.

How can I escape the characters required in bash? I'm not familiar with the language, so am not sure where to start. Replacing ' with \' would do the job at minimum I suspect.

Answer 1

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 '猫に小判' | jq -aRs . "\u732b\u306b\u5c0f\u5224\n" 

$ printf 'ô\nè\nà\n' | jq -Rs . "ô\nè\nà\n" 

To explain,

• -a means "ascii output" (omitted in the second example)
• -R means "raw input"
• -s means "include linebreaks" (mnemonic: "slurp")
• . 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 -aRs .` 

Answer 2

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"