When developing shell scripts that require HTTP interactions, a common question arises: can we reliably assume cURL is present across Unix-like systems? While cURL is indeed widely available, its default installation status varies between distributions:

# Quick test to check cURL availability
if command -v curl &> /dev/null; then
    echo "cURL is available"
else
    echo "cURL not found - fallback needed"
fi

From recent testing and documentation review:

• macOS: Included since OS X 10.4 (Tiger)
• Ubuntu/Debian: Installed by default since Ubuntu 12.04
• CentOS/RHEL: Present in minimal installations since RHEL 6
• FreeBSD: Included in base system since 5.0-RELEASE
• Alpine Linux: Not in base image (requires apk add curl)

For robust scripts that need to work across environments:

#!/bin/sh

# Define download function with fallback
download_file() {
    if command -v curl &> /dev/null; then
        curl -sL "$1" -o "$2"
    elif command -v wget &> /dev/null; then
        wget -q "$1" -O "$2"
    else
        echo "Error: Neither curl nor wget available" >&2
        exit 1
    fi
}

# Example usage
download_file "https://example.com/data.json" "local_data.json"

Common installation commands across distributions:

# Debian/Ubuntu
sudo apt-get install curl -y

# RHEL/CentOS
sudo yum install curl

# Alpine Linux
apk add curl

# macOS (Homebrew)
brew install curl

• Always check for cURL availability at script start
• Provide clear error messages when requirements aren't met
• Consider including installation instructions in your documentation
• For critical systems, document the minimum required cURL version

While cURL's presence is increasingly common, truly portable scripts should either declare it as a requirement or implement fallback mechanisms. The trend among modern Unix-like systems is to include cURL by default, except for extremely minimal installations.

From my experience working across various Unix-like systems, cURL has become increasingly standard over the past decade. While it wasn't always guaranteed to be pre-installed, most modern distributions now include it by default:

# Checking cURL installation on most systems:
which curl || echo "cURL not found"

# Sample download using cURL:
curl -O https://example.com/datafile.zip

Here's a breakdown of where you'll typically find cURL:

• Linux (Debian/Ubuntu): Included in base installations since Ubuntu 12.04
• macOS: Pre-installed since OS X 10.4 (Tiger)
• FreeBSD/OpenBSD: Available in base system since 2010s
• Minimal/Containerized Systems: May require explicit installation

For production scripts that need maximum compatibility, consider this pattern:

#!/bin/bash

# Check for cURL or fall back to wget
if command -v curl &> /dev/null; then
  DOWNLOAD="curl -sL -o"
elif command -v wget &> /dev/null; then
  DOWNLOAD="wget -q -O"
else
  echo "Error: Neither curl nor wget found" >&2
  exit 1
fi

# Usage example:
$DOWNLOAD output.file https://example.com/data

In environments where you control the deployment (like Docker containers), explicitly declare the dependency:

# Dockerfile example for Debian-based systems
FROM debian:stable-slim
RUN apt-get update && apt-get install -y curl

Understanding why cURL often becomes the preferred choice: