Parse environment placeholders (useful when using Docker for example)

replace_envs.sh

#!/bin/bash

# Replace variables $ENV{<environment varname>}
# (optional: $ENV{<environment varname>??<default value>}
# ----


function ReplaceEnvironmentVariable() {
    # - Parse environment variable placeholders.
    # - The format should be $ENV{***} where *** should match
    #   the exact name of the environment variable.
    # - Use ?? to specify a default value in case the
    #   environment variable was not found.
    # - Regex characters should be escaped before parsing!
    grep -rl "\$ENV{$1\(??[^}]*\)\?}" $3|xargs -r \
        sed -i "s/\$ENV{$1[^}]*}/$2/g"
}

function DefaultEnvironmentVariable() {
    REGEXP="\$ENV{[^??]*??\([^}]*\)}"

    grep -rl -- "$REGEXP" $1|xargs -r \
        sed -i "s/$REGEXP/\1/g"
}

# Replace all variables
for _curVar in `env | awk -F = '{print $1}'`;do
    # - 'awk' has split them by the equals sign.
    # - Pass the name and value to our function
    # - Works only in environments supporting indirect expansion like bash
    ReplaceEnvironmentVariable ${_curVar} ${!_curVar} /etc/nginx/conf.d/*
    ReplaceEnvironmentVariable ${_curVar} ${!_curVar} /etc/nginx/sites-available/*

    DefaultEnvironmentVariable /etc/nginx/conf.d/*
    DefaultEnvironmentVariable /etc/nginx/sites-available/*
done