![]() ![]() ![]() ![]() This can be useful while working with large JSON structures when we are only interested in several properties or values. This means we will start two indexes from the end (-2), and since the second argument is empty, it will run until the end of the array.įrequently when working with data structures such as JSON, we might want to transform one data structure into another. Note the subtle difference in the second slice - we pass the index as the first argument. The second slicing operation has a negative argument, which denotes in this case that it counts backward from the end of the array. , the slice will start from the beginning of the array and run up until index 6. Since we specified only the second argument in. It’s also possible to omit one of the indexes when using the slicing functionality: echo '' | jq '.' | jq '.' The result will be a new array with a length of 3, containing the elements from index 6 (inclusive) to index 9 (exclusive): [ This is particularly useful when we need to return a subarray of an array.Īgain, let’s see this using a simple array of numbers: echo '' | jq '.' Accessing by Indexįinally, jq also supports slicing of arrays, another powerful feature. We can also use a slightly more concise version and access the property directly on each object in the array: jq '.name' fruits.json 4.2. The last step is to output the name field from each object using. Then we can pass each object in the array to the next filter in the command using a pipe |. name' fruits.jsonįirst, we iterate over the array using. Let’s see how to extract the name of each fruit from each object in the array: jq '. Now let’s imagine we want to represent a list of fruit in a JSON document: [Įach item in the array is an object that represents a fruit. in use, which will print out each item in the array on a separate line: "x" Here, we see the object value iterator operator. Here, we use jq's notation to access Senator Ernst's terms as an attribute: take care to notice the square brackets which denote the array that is contained in terms: cat ernst.json | jq '.We’ll start with a basic example to demonstrate how to iterate over an array: echo '' | jq '.' Jeremiah,"Springfield, Jr.",Jebediah,1942,2003,M,Kalamazoo,Michigan Lucy Jo Mary,Carrie-Paulson,1967,F,Omaha,Nebraska JSON is more verbose, but easier to read than CSV.ĬSV: firstname,lastname,middlename,birthyear,deathyear,gender,city,stateĪlexander,Smith,Johnson,1918,1955,M,Madison,Wisconsin To install jq: # download directly into ~/bin_compcivĬheck out the tutorial on jq here. If you've haven't installed the pup HTML parsing tool, or any other tool which required you to edit your ~/.bashrc's' PATH and create the ~/bin_compciv directory, then follow the instructions here: Installing programs for your personal Stanford account. You can use it to slice and filter and map and transform structured data with the same ease that sed, awk, grep and friends let you play with text. Jq is a program described as " sed for JSON data": JSON stands for JavaScript Object Notation and is nearly ubiquitous as a data format, for its lightweight nature and (relatively) ease of human-readability. Most of the popular API and data services use the JSON data format, so we'll learn how it's used to serialize interesting information, and how to use the jq to parse it at the command-line. jq is a command-line tool for parsing JSON. JSON is a lightweight format that is nearly ubiquitous for data-exchange. ![]()
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