Sanitize a string for json [duplicate] - bash

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 -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 .`

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"

Answer 3

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' )

Answer 4

I was also trying to escape characters in Bash, for transfer using JSON, when I came across this. I found that there is actually a larger list of characters that must be escaped – particularly if you are trying to handle free form text.
There are two tips I found useful:
Use the Bash ${string//substring/replacement} syntax described in this thread.
Use the actual control characters for tab, newline, carriage return, etc. In vim you can enter these by typing Ctrl+V followed by the actual control code (Ctrl+I for tab for example).
The resultant Bash replacements I came up with are as follows:
JSON_TOPIC_RAW=${JSON_TOPIC_RAW//\\/\\\\} # \
JSON_TOPIC_RAW=${JSON_TOPIC_RAW//\//\\\/} # /
JSON_TOPIC_RAW=${JSON_TOPIC_RAW//\'/\\\'} # ' (not strictly needed ?)
JSON_TOPIC_RAW=${JSON_TOPIC_RAW//\"/\\\"} # "
JSON_TOPIC_RAW=${JSON_TOPIC_RAW// /\\t} # \t (tab)
JSON_TOPIC_RAW=${JSON_TOPIC_RAW//
/\\\n} # \n (newline)
JSON_TOPIC_RAW=${JSON_TOPIC_RAW//^M/\\\r} # \r (carriage return)
JSON_TOPIC_RAW=${JSON_TOPIC_RAW//^L/\\\f} # \f (form feed)
JSON_TOPIC_RAW=${JSON_TOPIC_RAW//^H/\\\b} # \b (backspace)
I have not at this stage worked out how to escape Unicode characters correctly which is also (apparently) required. I will update my answer if I work this out.

Answer 5

OK, found out what to do. Bash supports this natively as expected, though as always, the syntax isn't really very guessable!
Essentially ${string//substring/replacement} returns what you'd image, so you can use
MSG=${MSG//\'/\\\'}
To do this. The next problem is that the first regex doesn't work anymore, but that can be replaced with
git log -n 1 --pretty=format:'%s'
In the end, I didn't even need to escape them. Instead, I just swapped all the ' in the JSON to \". Well, you learn something every day.

Answer 6

git log -n 1 --format=oneline | grep -o ' .\+' | jq --slurp --raw-input
The above line works for me. refer to
https://github.com/stedolan/jq for more jq tools

Answer 7

I found something like that :
MSG=`echo $MSG | sed "s/'/\\\\\'/g"`

Answer 8

The simplest way is using jshon, a command line tool to parse, read and create JSON.
jshon -s 'Your data goes here.' 2>/dev/null

Answer 9

[...] with an apostrophe in it, the JSON is invalid.
Not according to https://www.json.org. A single quote is allowed in a JSON string.
How can I escape the characters required in bash?
You can use xidel to properly prepare the JSON you want to POST.
As https://example.com can't be tested, I'll be using https://api.github.com/markdown (see this answer) as an example.
Let's assume 'çömmít' "mêssågè" as the exotic output of git log -n 1 --pretty=format:'%s'.
Create the (serialized) JSON object with the value of the "text"-attribute properly escaped:
$ git log -n 1 --pretty=format:'%s' | \
xidel -se 'serialize({"text":$raw},{"method":"json","encoding":"us-ascii"})'
{"text":"'\u00E7\u00F6mm\u00EDt' \"m\u00EAss\u00E5g\u00E8\""}
Curl (variable)
$ eval "$(
git log -n 1 --pretty=format:'%s' | \
xidel -se 'msg:=serialize({"text":$raw},{"method":"json","encoding":"us-ascii"})' --output-format=bash
)"
$ echo $msg
{"text":"'\u00E7\u00F6mm\u00EDt' \"m\u00EAss\u00E5g\u00E8\""}
$ curl -d "$msg" https://api.github.com/markdown
<p>'çömmít' "mêssågè"</p>
Curl (pipe)
$ git log -n 1 --pretty=format:'%s' | \
xidel -se 'serialize({"text":$raw},{"method":"json","encoding":"us-ascii"})' | \
curl -d#- https://api.github.com/markdown
<p>'çömmít' "mêssågè"</p>
Actually, there's no need for curl if you're already using xidel.
Xidel (pipe)
$ git log -n 1 --pretty=format:'%s' | \
xidel -s \
-d '{serialize({"text":read()},{"method":"json","encoding":"us-ascii"})}' \
"https://api.github.com/markdown" \
-e '$raw'
<p>'çömmít' "mêssågè"</p>
Xidel (pipe, in-query)
$ git log -n 1 --pretty=format:'%s' | \
xidel -se '
x:request({
"post":serialize(
{"text":$raw},
{"method":"json","encoding":"us-ascii"}
),
"url":"https://api.github.com/markdown"
})/raw
'
<p>'çömmít' "mêssågè"</p>
Xidel (all in-query)
$ xidel -se '
x:request({
"post":serialize(
{"text":system("git log -n 1 --pretty=format:'\''%s'\''")},
{"method":"json","encoding":"us-ascii"}
),
"url":"https://api.github.com/markdown"
})/raw
'
<p>'çömmít' "mêssågè"</p>

Answer 10

This is an escaping solution using Perl that escapes backslash (\), double-quote (") and control characters U+0000 to U+001F:
$ echo -ne "Hello, 🌵\n\tBye" | \
perl -pe 's/(\\(\\\\)*)/$1$1/g; s/(?!\\)(["\x00-\x1f])/sprintf("\\u%04x",ord($1))/eg;'
Hello, 🌵\u000a\u0009Bye

Answer 11

I struggled with the same problem. I was trying to add a variable on the payload of cURL in bash and it kept returning as invalid_JSON. After trying a LOT of escaping tricks, I reached a simple method that fixed my issue. The answer was all in the single and double quotes:
curl --location --request POST 'https://hooks.slack.com/services/test-slack-hook' \
--header 'Content-Type: application/json' \
--data-raw '{"text":'"$data"'}'
Maybe it comes in handy for someone!

Answer 12

I had the same idea to send a message with commit message after commit.
First i tryed similar was as autor here.
But later found a better and simpler solution.
Just created php file which is sending message and call it with wget.
in hooks/post-receive :
wget -qO - "http://localhost/git.php"
in git.php:
chdir("/opt/git/project.git");
$git_log = exec("git log -n 1 --format=oneline | grep -o ' .\+'");
And then create JSON and call CURL in PHP style

Answer 13

Integrating a JSON-aware tool in your environment is sometimes a no-go, so here's a POSIX solution that should work on every UNIX/Linux:
json_stringify() {
[ "$#" -ge 1 ] || return 1
LANG=C awk '
BEGIN {
for ( i = 1; i <= 127; i++ )
repl[ sprintf( "%c", i) ] = sprintf( "\\u%04x", i )
for ( i = 1; i < ARGC; i++ ) {
s = ARGV[i]
printf("%s", "\"")
while ( match( s, /[\001-\037\177"\\]/ ) ) {
printf("%s%s", \
substr(s,1,RSTART-1), \
repl[ substr(s,RSTART,RLENGTH) ] \
)
s = substr(s,RSTART+RLENGTH)
}
print s "\""
}
exit
}
' "$#"
}
Or using the widely available perl:
json_stringify() {
[ "$#" -ge 1 ] || return 1
LANG=C perl -le '
for (#ARGV) {
s/[\x00-\x1f\x7f"\\]/sprintf("\\u%04x",ord($0))/ge;
print "\"$_\""
}
' -- "$#"
}
Then you can do:
json_stringify '"foo\bar"' 'hello
world'
"\u0022foo\bar\u0022"
"hello\u000aworld"
limitations:
Doesn't handle NUL bytes.
Doesn't validate the input for UNICODE, it only escapes the mandatory ASCII characters specified in the RFC 8259.
Replying to OP's question:
MSG=$(git log -n 1 --format=oneline | grep -o ' .\+')
curl -i -X POST \
-H 'Accept: application/text' \
-H 'Content-type: application/json' \
-d '{"payload": {"message": '"$(json_stringify "$MSG")"'}}' \
'https://example.com'