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1. Introduction

The INI file is one of the primary means of specifying the configuration input for various programs. Bash arrays support associative arrays in Bash, and we can use these to associate a key with a value, similar to a hashtable.

In this tutorial, we’ll learn how to convert an INI file to a Bash array in memory using basic primitives in scripting.

2. INI File Layout

First, let’s see a sample INI file, test.ini, as an example:

; last modified 1 April 2001 by John Doe
[owner]
name = John Doe
organization = Acme Widgets Inc.
[database]
; use IP address in case network name resolution is not working
server = 192.0.2.62     
port = 143
file = "payroll.dat"

In detail, the INI file has a set of sections. A unique name identifies a section. The square brackets enclose the section names.

Each section has a set of key-value pairs. In a similar fashion, key-value pairs are in the form of key=value. We ignore any other format of the line.

Next, we’ll build various parts of the script that parses the INI file and fills up the array.

3. Parsing and Building the Array

We’ll follow a few simple steps to parse the file and build the array:

  1. Read each line from the file as a string.
  2. Parse the string to get the section name or key-value pair.
  3. Build a unique key name using the section and key name and store the value in the bash array.

3.1. Parse a Section Name

First, we have to parse a given input string. We can retrieve the section name from the input string:

#!/usr/bin/env bash 
# declare an associative array using -A option 
declare -A inidb
function _ini_get_section {
    if [[ "$1" =~ ^(\[)(.*)(\])$ ]]; 
    then 
        echo ${BASH_REMATCH[2]} ; 
    else 
        echo ""; 
    fi
}

Here, we declare a global variable inidb as an associative array, which we’ll use throughout the script. This is the array that will be filled by reading the INI file. We’re using the regular expression ^([)(.*)(])$ which matches any string that begins with a square bracket and ends with a square bracket. The string between the square brackets is retrieved as the section name. The function takes a string as an input parameter.

3.2. Parse the Key-Value Pair

In order to get the key-value pair, we retrieve the key and associated value from the input string:

function _ini_get_key_value {
    if [[ "$1" =~ ^([^=]+)=([^=]+)$ ]]; 
    then 
        echo "${BASH_REMATCH[1]}=${BASH_REMATCH[2]}"; 
    else 
        echo ""
    fi
}

To emphasize, we’re using the regular expression^([^=]+)=([^=]+)$ which matches any string of the form KEY=VALUE. This function acts as validation for the strings that follow the INI file format. It returns the string in the form of KEY=VALUE. The caller of the function can post-process it to split it into parts.

3.3. Reading and Building the Array

At this point, we have to stitch all the pieces together to build the array. By and large, there are only two steps:

  1. Open and read the file one line at a time.
  2. Parse and populate the array.

In order to do the above, let’s write a function:

function ini_loadfile {
    local cur_section=""
    local cur_key=""
    local cur_val=""
    IFS=
    while read -r line; do
        new_section=$(_ini_get_section $line)
        # got a new section
        if [[ -n "$new_section" ]]; then
            cur_section=$new_section
        # not a section, try a key value
        else
            val=$(_ini_get_key_value $line)
            # trim the leading and trailing spaces as well
            cur_key=$(echo $val | cut -f1 -d'=' | sed -e 's/^[[:space:]]*//' | sed -e 's/[[:space:]]*$//') 
            cur_val=$(echo $val | cut -f2 -d'=' | sed -e 's/^[[:space:]]*//' | sed -e 's/[[:space:]]*$//')
        if [[ -n "$cur_key" ]]; then
            # section + key is the associative in bash array, the field seperator is space
            inidb[${cur_section} ${cur_key}]=$cur_val
        fi
    fi
    done <$1
}

As we can see, we’re reading the given file line by line. We’re able to do it line by line using the separator specified with IFS. This is important since some of the values may have spaces. Bash uses spaces as a separator. By specifying IFS as an empty string, we’re able to read the file one line at a time.

We use the functions _ini_get_section and _ini_get_key_value to allow us to pick out section names and key-value pairs from each line. Finally, we store the value in an associative array, inidb. We also trim the leading and trailing spaces for the key and value using the sed command.

3.4. Putting It All Together

Now that we have all the building blocks, we can read an INI file into a Bash array using all the above functions:

function ini_printdb {
    for i in "${!inidb[@]}"
    do
    # split the associative key in to section and key
       echo -n "section  : $(echo $i | cut -f1 -d ' ');"
       echo -n "key  : $(echo $i | cut -f2 -d ' ');"
       echo  "value: ${inidb[$i]}"
    done
}
function ini_get_value {
    section=$1
    key=$2
    echo "${inidb[$section $key]}"
}
ini_loadfile test.ini
ini_printdb

To clarify, we have written two functions. ini_printdb prints the INI database. ini_get_value gets the key and value based on the specified section and key name. 

In summary, the complete program using all the above-developed functions is saved as inidb.sh.

At this point, let’s look at the sample output on running the above program:

$ ./inidb.sh test.ini 
section  : owner;key  : name;value: John Doe
section  : database;key  : file;value: "payroll.dat"
section  : owner;key  : organization;value: Acme Widgets Inc.
section  : database;key  : port;value: 143
section  : database;key  : server;value: 192.0.2.62

In brief, we have read the file, stored the file contents in the Bash array, and printed the contents of the array.

4. Conclusion

In this article, we saw how we can convert an INI file into a Bash array by parsing the file and getting values from it based on the section and key names.

Authors Bottom

If you have a few years of experience in the Linux ecosystem, and you’re interested in sharing that experience with the community, have a look at our Contribution Guidelines.

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