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I'm having a hard time getting the value of an environment variable ($GHREPO) in a quoted string. Here is the command I'm running. I'm trying to make a directory with the value of j["ChgSub"][$GHREPO][0]["Major"], $GHREPO being an environment variable.

 mkdir `cat ../dummy.json | 
 ruby -rjson -e 'j = JSON.parse($stdin.read); puts j["ChgSub"][$GHREPO][0]["Major"].to_s'`

Edit: dummy.json content

{

  "ChgSub": {
    "ecx": [
      {
        "Major": 0,
        "Minor": 0,
        "Patch": 3
      }
    ]
  }
}
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3 Answers 3

Reset to default
3

Variables don't get evaluated in a single quoted string. You need to use double quotes. If you can't or don't want to use double quotes for the whole string you can use them for just that part of the string.

ruby -rjson -e 'j = JSON.parse($stdin.read); puts j["ChgSub"]["'"$GHREPO"'"][0]["Major"].to_s'

That is three separate quoted strings next to one another.

'j = JSON.parse($stdin.read); puts j["ChgSub"]["'

and

"$GHREPO"

and

'"][0]["Major"].to_s'
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  • It still errors out so I can only assume the environment variable is not correctly parsed because if I replace it with the actual string it works. mkdir cat dummy.json | ruby -rjson -e 'j = JSON.parse($stdin.read); puts j["ChgSub"]["'"$GHREPO"'"][0]["Major"].to_s'` Commented Nov 26, 2014 at 23:22
  • @mihai What is the value of GHREPO? Commented Nov 26, 2014 at 23:52
  • A string... "ecx". I've updated the question with the json content as well. To reproduce the issue you need to set export GHREPO=ecx and run the command Commented Nov 27, 2014 at 0:02
  • @Etan, I finally got it though have my vote anyway as it's close to your answer! Commented Nov 27, 2014 at 0:52
2

You should always avoid mixing languages as much as possible. In this case you are trying to mix shell script into ruby script. Mixing languages convolutes your code and makes it fragile.

The solution in this case is to use ruby's native environment variable support.

$ GHREPO=ecx ruby -rjson -e 'j = JSON.parse($stdin.read); puts j["ChgSub"][ENV["GHREPO"]][0]["Major"].to_s' < dummy.json
0

To make this even clearer, I would use a heredoc, and not a quoted argument:

$ export GHREPO=ecx
$ ruby -rjson - dummy.json <<'EOF'
> j = JSON.parse(File.read(ARGV[0]))
> puts j["ChgSub"][ENV["GHREPO"]][0]["Major"].to_s
> EOF
0

Using a heredoc, you no longer have to fight with embedding single quotes within double quotes, escaping, etc.

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0

It should be '"'$GHREPO'"' so the command is 

cat dummy.json | ruby -rjson -e 'j = JSON.parse($stdin.read);
   puts j["ChgSub"]['"'$GHREPO'"'][0]["Major"].to_s'

@Etan was pretty close to the answer.

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3
  • This generates the same output as mine only it uses single quotes on ['exc'] instead of double quotes ["exc"]. echo both the ruby command strings to see that. Commented Nov 27, 2014 at 3:30
  • Not really... '"'$GHREPO'"' is not same as "'"$GHREPO"'" . The ruby command starts a single quoted string rjson -e 'j = and that's why your solution fails. Commented Nov 27, 2014 at 4:16
  • '...['"'$BAR'"']...' is '...[', "'$BAR'", ']...' which evaluates (when BAR=exc) to '...[', "'foo'", ']...'. Which when pasted together and unquoted becomes ...['foo'].... '...["'"$BAR"'"]...', in contrast, is '...["', "$BAR", '"]...' -> '...["', "exc", '"]...' -> ...["exc"].... Commented Nov 28, 2014 at 14:23

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