Trying to swap JSON element using sed editor on MAC - macos

Question

I am trying to create a script to find a JSON element and update it with the arg values.
#!/bin/bash
# Shell script to verify the end to end D1 request flow
placeLocation=$1
vehicleHeading=$2
message=$3
file=one.txt
sed -i '' '/location/c\ \"location\" : \"$placeLocation\",' $file
sed -i '' '/heading/c\ \"heading\" : \"$vehicleHeading\",' $file
sed -i '' '/message/c\ \"message\" : \"$message\",' $file
One.txt
"location":"<48.777098,9.181301> - 150.0m",
"message":"Hello there!",
"heading": "34",
But getting following error
sed: 1: "/location/c\ \"locati ...": extra characters after \ at the end of c command
sed: 1: "/heading/c\ \"heading ...": extra characters after \ at the end of c command
sed: 1: "/message/c\ \"message ...": extra characters after \ at the end of c command
sed: 1: "file.txt": invalid command code f
sed: 1: "file.txt": invalid command code f
sed: 1: "file.txt": invalid command code f
sed: 1: "file.txt": invalid command code f
I have just started learning about sed editor and tried out multiple things but couldn't able to figure it out. Any help is much appreciated!

Answer 1

Note that you probably should consider using a tool like jq for editing JSON files. But I assume you have a good reason for using sed, so you have a couple of problems there.
The first is that you're trying to use GNU sed features on your Mac OS X version of sed that doesn't have those features. If you want GNU sed on Mac OS X, then install it:
▶ brew install gnu-sed
Fixing up your code for GNU sed (and also for other Bash style guide recommendations about quoting strings):
cat > FILE <<EOF
"location":"<48.777098,9.181301> - 150.0m",
"message":"Hello there!",
"heading": "34",
EOF
placeLocation=myPlaceLocation
vehicleHeading=myVehicleHeading
message=myMessage
file=FILE
gsed -i -e '/location/c\' -e '"location": "'"$placeLocation"'",' "$file"
gsed -i -e '/heading/c\' -e '"heading": "'"$vehicleHeading"'",' "$file"
gsed -i -e '/message/c\' -e '"message": "'"$message"'",' "$file"
As noted in the GNU sed manual, use of multiple -e commands on the same line with the c\ command is a GNU extension.
If you want to use Mac OS X's sed, just may be able to write it this way:
sed -i '' '
s/"location".*/"location": "'"$placeLocation"'",/
s/"heading".*/"heading": "'"$vehicleHeading"'",/
s/"message".*/"message": "'"$message"'",/
' "$file"
But note you would have to sanitise the input if you need the code to be robust to all inputs.

Answer 2

To do this robustly you need to use a tool that understands literal strings (which sed doesn't - see Is it possible to escape regex metacharacters reliably with sed) e.g. awk:
$ awk 'BEGIN{FS=OFS=":"; val=ARGV[1]; ARGV[1]=""} $1=="\"message\""{sub(FS".*",FS); print $1, "\""val"\""}' 'what is 1/2?' one.txt
"message":"what is 1/2?"
$ awk 'BEGIN{FS=OFS=":"; val=ARGV[1]; ARGV[1]=""} $1=="\"message\""{sub(FS".*",FS); print $1, "\""val"\""}' 'what is 1&2?' one.txt
"message":"what is 1&2?"
$ awk 'BEGIN{FS=OFS=":"; val=ARGV[1]; ARGV[1]=""} $1=="\"message\""{sub(FS".*",FS); print $1, "\""val"\""}' 'what is \1?' one.txt
"message":"what is \1?"
the above will work robustly using any awk in any shell on every UNIX box. Try using those as replacement strings in a sed command.
The full script to do what you want would be:
#!/bin/env bash
# Shell script to verify the end to end D1 request flow
placeLocation=$1
vehicleHeading=$2
message=$3
file=one.txt
tmp=$(mktemp)
awk '
BEGIN {
split("location heading message", tags)
for (i in tags) {
vals["\"" tags[i] "\""] = "\"" ARGV[i] "\""
ARGV[i] = ""
}
FS=OFS=":"
}
$1 in vals {
tag = $1
sub(FS".*","")
$0 = tag OFS vals[tag]
}
1' "$placeLocation" "$vehicleHeading" "$message" "$file" > "$tmp" && mv "$tmp" "$file"