assign jq result to variable bash

Guide to Passing Bash Variables to jq

  • By Syed Wahaj

assign jq result to variable bash

Table of Contents

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Introduction:

jq is a powerful command-line tool for processing and manipulating JSON data in Bash. It allows you to extract specific values, filter data, and transform JSON structures. In this guide, we will explore how to pass Bash variables to jq and perform dynamic JSON processing based on the variable values.

Prerequisites:

  • Basic knowledge of Bash scripting.
  • jq installed on your system. You can install it using your package manager (e.g., apt , yum , brew , etc.).

Using Variables with jq :

To pass Bash variables to jq , you can use the --arg or --argjson options provided by jq . These options allow you to define variables within the jq command and access them in the JSON processing logic.

Passing String Variables:

You can pass string variables to jq using the --arg option. Here’s an example:

In this example, we define two Bash variables, name and age . We create a JSON string called json with placeholders $name and $age . Then, we pass the variables to jq using the --arg option. Finally, we execute the jq command, and the result is stored in the result variable and printed to the console.

Passing Numeric or Complex Variables:

If you need to pass numeric or more complex variables (such as arrays or objects), you can use the --argjson option. Here’s an example:

In this example, we define a Bash variable called values that contains a JSON array. We pass the variable to jq using the --argjson option. The filter variable specifies the jq filter to apply ( [] is used to select all elements of the array). The jq command is executed, and the result is stored in the result variable and printed to the console.

Advanced Techniques for Passing Variables to jq :

Variable expansion:.

You can also use variable expansion within jq filters to access Bash variables directly. Here’s an example:

In this example, we use the jq filter to directly access the Bash variables $name and $age within the JSON string. By enclosing the filter in double quotes ( " " ), Bash performs variable expansion before passing the command to jq . The result is stored in the result variable and printed to the console.

Passing Variables from Command Line Arguments:

If you want to pass variables from command line arguments to jq , you can use the $1 , $2 , etc., variables to access the arguments. Here’s an example:

In this example, we assign the first command line argument to the name variable and the second argument to the age variable. We then pass these variables to jq using the --arg option. Running the script with arguments like ./script.sh "John Doe" 30 will produce the desired JSON output.

Conclusion:

Passing Bash variables to jq provides flexibility and dynamic processing capabilities when working with JSON data. By using --arg and --argjson options, variable expansion, and command line arguments, you can incorporate variables into your jq commands and perform customized JSON processing. Experiment with different scenarios and explore the rich features of jq to harness the power of JSON manipulation in your Bash scripts.

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Using bash variables in jq

Due to the special characters used in json, the easiest way to use jq with inline scripts it by putting it between single quotes. That makes it impossible to use bash variables inside your script . Fortunately, jq has an --arg parameter to create a predefined variable from an external source.

You can use it to define a $foo variable with the contents of bash variable $FOO , for example:

You might notice the -n parameter: This tells jq to use null as input instead of reading json from stdin like it normally would. I'm using it in all examples on this page as it makes them a bit shorter. In real world usage you probably won't need it.

As usual in bash scripts you can also execute a command inline:

Every variable created with --arg is treated as a string . That might cause some unexpected behaviour when you work with numbers, like when you attempt to add a number to an argument. Comparisons between strings and numbers seem to work fine, but I wouldn't count on it (pun intended).

There are two ways to solve this: either convert the variable to a number with tonumber or use --argjson instead. I prefer to use tonumber because that way I'm sure jq forces it to be a number. As my argument may be the result of an earlier command, I may be using an error message as input instead of the expected numeric result.

Variables from files

It's also possible to load variables from files. With --slurpfile we can read a file containing json objects. An array containing the separate objects is then made available as a predefined variable. Note that even if your file contains only a single json object, as the variable is still an array, the [0] is required to access it.

A second option is --rawfile , creating a string variable with the exact contents of the file. Note that as jq outputs json, reading and printing the file from the previous example results an escaped string.

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COMMENTS

  1. Setting jq output to a Bash Variable

    The present solution with read is useful when you need to assign multiple keys to multiple shell variables in one shot; you then just need to use read var1 var2 var3 < <(...). Here are more general snippets to assign jq output to shell variables, that can be very handy. Two methods for single-line input (without loop):

  2. jq: How do I assign a jq output to a variable?

    jq: How do I assign a jq output to a variable? Ask Question Asked 1 year, 6 months ago. Modified 1 year, 6 months ago. Viewed 4k times ... How to extract value from json contained in a variable using jq in bash. 0. JQ : Output with static value / variable. 0. JQ Not Taking In Variable Data. 1.

  3. Guide to Passing Bash Variables to jq

    Further, let's assume that we want to override the value of the fruit field with a user-defined value that's available through the bash_fruit_var Bash variable: $ bash_fruit_var=Banana. Next, let's go ahead and write a jq program using the -arg option to display the fruit field from the bash_fruit_var variable and all other field values from the fruits_template.json file using the ...

  4. Parsing JSON output to variable in bash using jq filters

    Parsing JSON output to variable in bash using jq filters. Ask Question Asked 1 year, 3 months ... Getting the result into a shell variable is then a matter of running the pipeline in a command substitution and assigning it to a variable: ... Look at the result of the curl request and whether the response looks very different from what you ...

  5. How to work with JSON in BASH using jq?

    jq in a BASH script. Let's go ahead and create a small bash script which should output the following information for us: Get only the first question from the output; Get all of the answers for that question; Assign the answers to variables; Print the question and the answers; To do that I've put together the following script:

  6. jq

    Tour Start here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site

  7. Guide to Passing Bash Variables to jq

    In this example, we define a Bash variable called values that contains a JSON array. We pass the variable to jq using the --argjson option. The filter variable specifies the jq filter to apply ([] is used to select all elements of the array). The jq command is executed, and the result is stored in the result variable and printed to the console.. Advanced Techniques for Passing Variables to jq:

  8. Using bash variables in jq

    Due to the special characters used in json, the easiest way to use jq with inline scripts it by putting it between single quotes. That makes it impossible to use bash variables inside your script. Fortunately, jq has an --arg parameter to create a predefined variable from an external source.

  9. json

    This is the only 100%-safe answer; it lets jq properly create the filter using the value, rather than using bash to create a string that jq interprets as a filter. (Consider what happens if the value of EMAILID contains a ) .)

  10. Bash Assign Output of Shell Command To Variable

    You learned how to assign output of a Linux and Unix command to a bash shell variable. For more information see GNU bash command man page here and read the following docs: Command substitution - from the Linux shell scripting tutorial wiki. See man pages using the help/man command: $ man bash $ help printf $ help echo $ man 1 printf

  11. bash

    A shell assignment is a single word, with no space after the equal sign. So what you wrote assigns an empty value to thefile; furthermore, since the assignment is grouped with a command, it makes thefile an environment variable and the assignment is local to that particular command, i.e. only the call to ls sees the assigned value.. You want to capture the output of a command, so you need to ...

  12. How do I set a variable to the output of a command in Bash?

    As an aside, all-caps variables are defined by POSIX for variable names with meaning to the operating system or shell itself, whereas names with at least one lowercase character are reserved for application use. Thus, consider using lowercase names for your own shell variables to avoid unintended conflicts (keeping in mind that setting a shell variable will overwrite any like-named environment ...

  13. How to assign the output of a Bash command to a variable?

    You can also do way more complex commands, just to round out the examples above. So, say I want to get the number of processes running on the system and store it in the ${NUM_PROCS} variable.. All you have to so is generate the command pipeline and stuff it's output (the process count) into the variable.

  14. bash

    Pulling the comments from your previous question:. whitelist="whitelist_tmp.json" listlength=$(jq '. | length' "${whitelist}") mapfile -t rule < <(jq -r '.[].ruleId ...

  15. How to pass bash variable as a key to jq?

    In order to get the value of app, I can do this in jq as. jq '.app' But what I want is, I want to pass the key to jq as a bash variable, i.e. bash_var="app" jq '."${bash_var}"' I'm getting the output as null instead of the value. What is the correct syntax to achieve this?

  16. jq

    1. If both the input and map objects are in separate files we can use an alternative to Botje 's solution, were we read both object into a single array using the -s (slurp) option. Then we can. jq -s '.[1].type = .[0][.[1].type] | last' map input. Change .type (on second index) to the mapped value from the first index.