sed command issues

Question

Background

Original json (test.json): {"rpc-password": "password"}

Expected changed json: {"rpc-password": "somepassword"}

replace_json_str is a function used to replace password with somepassword using sed.

replace_json_str() {
    x=$1
    sed -i -e 's/\({ "'"$2"'":\)"[^"]*" }/\1"'"$3"'" }/g' $x
}

Unit test: replace_json_str test.json rpc-password somepassword

Issue

After running the above test, I get a file named test.json-e and the contents of the file is the same as before the test was ran, why?

Scott Stensland · Accepted Answer · 2017-03-11T14:52:52.993

there is a handy command line json tool called jq

cat input.json
{"rpc-password": "password"}

cat update_json.sh

givenkey=$1
givenvalue=$2

inputfile=input.json
outfile=output.json

cat $inputfile  | jq .   #  show input json

jq --arg key1 "$givenkey" --arg val1 "$givenvalue"  '.[$key1] = $val1' "$inputfile" > "$outfile"

cat "$outfile" | jq .     #  render output json

keep in mind jq can handle multiple such key value updates ... execute it

update_json.sh  rpc-password somepassword
{
  "rpc-password": "password"
}
{
  "rpc-password": "somepassword"
}

score 1 · Answer 2 · answered Mar 11 '17 at 02:39

1

Depends on which sed you're using.

The command you ran will work as expected with GNU sed.

But BSD sed does not allow for an empty argument to -i, and if you ran the same command, it will use the next argument, -e, as the backup file.

Also, the positioning of the spaces in your pattern don't match your example JSON.

answered Mar 11 '17 at 02:39

ephemient

198,619
38
280
391

Okay, so how would I change the spaces in the pattern to work? – Nicholas Adamou Mar 11 '17 at 02:40
apparently I am using BSD sed after a quick look. – Nicholas Adamou Mar 11 '17 at 02:41
I change the command to `sed -i "$1" -e 's/${ "'"$2"'":$"[^"]*" }/\1"'"$3"'" }/g'` inside `replace_json_str` and after running it I get `sed: -i may not be used with stdin` – Nicholas Adamou Mar 11 '17 at 02:45
That's not how you use it. It should be something like `sed -i .bak -e 's/${"'"$2"'": $"[^"]*"}/\1"'"$3"'"}/g' $x`. You'll end up with a `$x.bak` file which is the original, and an `$x` file which is modified. – ephemient Mar 11 '17 at 02:47
okay that works, but I don't want a `test.json.bak` after running the script. – Nicholas Adamou Mar 11 '17 at 02:51
1

With BSD sed, you don't have an option to skip the backup file. – ephemient Mar 11 '17 at 02:51
@ephemient: Actually, you do: use `-i ''`. – mklement0 Mar 11 '17 at 03:30
@mklement0 Okay, but then it doesn't work with GNU sed. – ephemient Mar 11 '17 at 04:32
@ephemient: [Indeed](http://stackoverflow.com/a/40777793/45375) - If you do not want a backup file created, there is no single `-i` syntax that works for both BSD and GNU sed. – mklement0 Mar 11 '17 at 04:37
Replace sed with perl -pe and will work everywhere... perl -pe has the same syntax as sed , including backreferences – George Vasiliou Mar 11 '17 at 12:24

sed command issues

2 Answers2