In the world of web development and system administration, HTTP clients are essential tools for interacting with web services. While many developers rely on popular utilities like curl or wget, it's both educational and sometimes necessary to create a basic HTTP client using nothing but Bash. This approach not only deepens our understanding of the HTTP protocol but also proves useful in environments where standard tools may not be available. Our Bash-based HTTP client supports the fundamental HTTP methods: GET, POST, PUT, DELETE, and OPTIONS. Here's a breakdown of its key components:

1. TCP Connection Handling The script uses Bash's built-in /dev/tcp/ pseudo-device to establish TCP connections. This feature, often overlooked, allows for raw socket programming directly in Bash.

   exec 3<>/dev/tcp/"$host"/80
   

   This line opens a bidirectional connection to the specified host on port 80, using file descriptor 3.
2. Request Formatting The script constructs HTTP requests using here-documents, ensuring proper formatting of headers and body content.

   echo -e "$method $path HTTP/1.1\r
   Host: $host\r
   Connection: close\r
   Content-Length: ${#data}\r
   \r
   $data" >&3
   

3. Response Handling After sending the request, the script reads the response using the cat command:

   cat <&3
   

   This simple approach captures both headers and body content.
4. Method-Specific Functions The script provides separate functions for each HTTP method, simplifying usage and improving readability. The complete Script is on my GitHub

#!/bin/bash

perform_request() {
    local method="$1"
    local url="$2"
    local data="$3"
    local host=$(echo "$url" | awk -F/ '{print $3}')
    local path=$(echo "$url" | awk -F/ '{print "/" $4}')

    exec 3<>/dev/tcp/"$host"/80

    echo -e "$method $path HTTP/1.1\r
Host: $host\r
Connection: close\r
Content-Length: ${#data}\r
\r
$data" >&3

    cat <&3
    exec 3>&-
}

get_request() {
    perform_request "GET" "$1" ""
}

post_request() {
    perform_request "POST" "$1" "$2"
}

put_request() {
    perform_request "PUT" "$1" "$2"
}

delete_request() {
    perform_request "DELETE" "$1" ""
}

options_request() {
    perform_request "OPTIONS" "$1" ""
}

# Usage examples
# get_request "http://example.com"
# post_request "http://example.com/api" "key1=value1&key2=value2"
# put_request "http://example.com/api/resource" "updated_data"
# delete_request "http://example.com/api/resource"
# options_request "http://example.com"

While this implementation is basic, it demonstrates the power and flexibility of Bash for networking tasks. It's particularly useful for quick tests, debugging, or in environments where installing additional tools is not feasible. In our next article, we'll explore the server-side of HTTP by building a simple CRUD server in Bash, rounding out our exploration of raw HTTP handling with Bash.