When working with the $http_proxy environment variable in Linux, many developers encounter situations where certain internal network resources shouldn't go through the proxy. Unlike GUI browsers that provide proxy exception settings, command-line tools and some applications rely solely on environment variables.

Here are several methods to handle proxy exceptions when using $http_proxy:

1. Using no_proxy Environment Variable

The most straightforward solution is to set the no_proxy environment variable alongside $http_proxy:

export http_proxy="http://proxy.example.com:8080"
export no_proxy="localhost,127.0.0.1,192.168.1.0/24,.internal.example.com"

2. Application-Specific Configuration

Some applications have their own proxy exception settings. For Chromium specifically:

chromium --proxy-server="http://proxy.example.com:8080" \
         --proxy-bypass-list="*.internal.example.com,192.168.*.*"

For more complex scenarios, consider these approaches:

PAC File Solution

Create a Proxy Auto-Config (PAC) file:

function FindProxyForURL(url, host) {
    // Bypass proxy for internal domains
    if (shExpMatch(host, "*.internal.example.com") ||
        isInNet(host, "192.168.1.0", "255.255.255.0")) {
        return "DIRECT";
    }
    // Use proxy for all other requests
    return "PROXY proxy.example.com:8080";
}

Then configure Chromium to use it:

chromium --proxy-pac-url="file:///path/to/proxy.pac"

Shell Script Wrapper

Create a wrapper script that dynamically adjusts proxy settings:

#!/bin/bash

# Check if target is in exception list
if [[ "$1" =~ ^192\.168\. ]] || [[ "$1" == "internal.example.com" ]]; then
    unset http_proxy https_proxy
else
    export http_proxy="http://proxy.example.com:8080"
    export https_proxy="$http_proxy"
fi

# Execute the original command
shift
exec "$@"

When proxy exceptions don't work as expected:

• Verify the no_proxy format - domains should be comma-separated without spaces
• Check for CIDR notation support in your application
• Test with curl -v to see if the proxy is being bypassed
• Remember that some applications may cache proxy settings

For persistent settings across all users, add these to /etc/environment:

http_proxy="http://proxy.example.com:8080"
no_proxy="localhost,127.0.0.1,.internal.example.com"

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When working behind corporate proxies in Linux environments, we often set the $http_proxy environment variable to route traffic through intermediary servers. However, many applications (like Chromium, wget, curl) that respect this variable don't natively support proxy exceptions - a critical requirement when accessing internal resources.

The most effective way to handle proxy exceptions is through the $NO_PROXY environment variable (sometimes called $no_proxy). This works alongside $http_proxy to define bypass rules:

export http_proxy="http://proxy.example.com:8080"
export HTTPS_PROXY="http://proxy.example.com:8080"
export no_proxy="localhost,127.0.0.1,192.168.1.0/24,.internal.example.com"

The variable accepts multiple formats for different matching scenarios:

• IP Addresses: 192.168.1.100
• IP Ranges: 192.168.1.0/24
• Domain Names: .example.com (matches all subdomains)
• Hostnames: internal-server

While many tools respect NO_PROXY, some require special handling:

For Chromium/Chrome

Create a wrapper script or modify your .bashrc:

#!/bin/bash
export no_proxy="localhost,127.0.0.1,192.168.*,.corp"
/usr/bin/chromium-browser --proxy-server="$http_proxy" --no-proxy-server="$no_proxy" "$@"

For cURL

cURL has excellent proxy exception support:

curl --noproxy "*.internal,192.168.*,localhost" https://internal-site

For System-wide Configuration

Add to /etc/environment for all users:

http_proxy="http://proxy.example.com:3128"
no_proxy="localhost,127.0.0.1,.localdomain,.example.com,192.168.1.0/24"

If exceptions aren't working:

1. Verify variable names (some tools expect lowercase no_proxy)
2. Check for IP range syntax support (CIDR notation may not work everywhere)
3. Test with basic patterns first (localhost)
4. Use env command to confirm environment variables are set