Parse JSON to array in a shell script

问题:

I'm trying to parse a JSON object within a shell script into an array.

e.g.: [Amanda, 25, http://mywebsite.com]

The JSON looks like:

{
  "name"       : "Amanda", 
  "age"        : "25",
  "websiteurl" : "http://mywebsite.com"
}

I do not want to use any libraries, it would be best if I could use a regular expression or grep. I have done:

myfile.json | grep name

This gives me "name" : "Amanda". I could do this in a loop for each line in the file, and add it to an array but I only need the right side and not the entire line.

回答1:

If you really cannot use a proper JSON parser such as jq^[1] , try an awk-based solution:

Bash 4.x:

readarray -t values < <(awk -F\" 'NF>=3 {print $4}' myfile.json)

Bash 3.x:

IFS=$'\n' read -d '' -ra values < <(awk -F\" 'NF>=3 {print $4}' myfile.json)

This stores all property values in Bash array ${values[@]}, which you can inspect with
declare -p values.

These solutions have limitations:

• each property must be on its own line,
• all values must be double-quoted,
• embedded escaped double quotes are not supported.

All these limitations reinforce the recommendation to use a proper JSON parser.

---

^{Note: The following alternative solutions use the Bash 4.x+ readarray -t values command, but they also work with the Bash 3.x alternative, IFS=$'\n' read -d '' -ra values.}

grep + cut combination: A single grep command won't do (unless you use GNU grep - see below), but adding cut helps:

readarray -t values < <(grep '"' myfile.json | cut -d '"' -f4)

---

GNU grep: Using -P to support PCREs, which support \K to drop everything matched so far (a more flexible alternative to a look-behind assertion) as well as look-ahead assertions ((?=...)):

readarray -t values < <(grep -Po ':\s*"\K.+(?="\s*,?\s*$)' myfile.json)

---

Finally, here's a pure Bash (3.x+) solution:

^{What makes this a viable alternative in terms of performance is that no external utilities are called in each loop iteration; however, for larger input files, a solution based on external utilities will be much faster.}

#!/usr/bin/env bash

declare -a values # declare the array                                                                                                                                                                  

# Read each line and use regex parsing (with Bash's `=~` operator)
# to extract the value.
while read -r line; do
  # Extract the value from between the double quotes
  # and add it to the array.
  [[ $line =~ :[[:blank:]]+\"(.*)\" ]] && values+=( "${BASH_REMATCH[1]}" )
done < myfile.json                                                                                                                                          

declare -p values # print the array

---

^{[1] Here's what a robust jq-based solution would look like (Bash 4.x):
readarray -t values < <(jq -r '.[]' myfile.json)}

回答2:

jq is good enough to solve this problem

paste -s <(jq '.files[].name' YourJsonString) <(jq '.files[].age' YourJsonString) <( jq '.files[].websiteurl' YourJsonString) 

So that you get a table and you can grep any rows or awk print any columns you want

回答3:

You can use a sed one liner to achieve this:

array=( $(sed -n "/{/,/}/{s/[^:]*:[[:blank:]]*//p;}" json ) )

Result:

$ echo ${array[@]}
"Amanda" "25" "http://mywebsite.com"

If you do not need/want the quotation marks then the following sed will do away with them:

array=( $(sed -n '/{/,/}/{s/[^:]*:[^"]*"\([^"]*\).*/\1/p;}' json) )

Result:

$ echo ${array[@]}
Amanda 25 http://mywebsite.com

It will also work if you have multiple entries, like

$ cat json
{
  "name"       : "Amanda" 
  "age"        : "25"
  "websiteurl" : "http://mywebsite.com"
}

{
   "name"       : "samantha"
   "age"        : "31"
   "websiteurl" : "http://anotherwebsite.org"
}

$ echo ${array[@]}
Amanda 25 http://mywebsite.com samantha 31 http://anotherwebsite.org

UPDATE:

As pointed out by mklement0 in the comments, there might be an issue if the file contains embedded whitespace, e.g., "name" : "Amanda lastname". In this case Amanda and lastname would both be read into seperate array fields each. To avoid this you can use readarray, e.g.,

readarray -t array < <(sed -n '/{/,/}/{s/[^:]*:[^"]*"\([^"]*\).*/\1/p;}' json2)

This will also take care of any globbing issues, also mentioned in the comments.