Linux – How to delete an exported environment variable

For use in scenarios where you need to set specific environment values for unit tests, you might find the following hack useful. It will change the environment variables throughout the JVM (so make sure you reset any changes after your test), but will not alter your system environment.

I found that a combination of the two dirty hacks by Edward Campbell and anonymous works best, as one of the does not work under linux, one does not work under windows 7. So to get a multiplatform evil hack I combined them:

protected static void setEnv(Map<String, String> newenv) throws Exception {
  try {
    Class<?> processEnvironmentClass = Class.forName("java.lang.ProcessEnvironment");
    Field theEnvironmentField = processEnvironmentClass.getDeclaredField("theEnvironment");
    theEnvironmentField.setAccessible(true);
    Map<String, String> env = (Map<String, String>) theEnvironmentField.get(null);
    env.putAll(newenv);
    Field theCaseInsensitiveEnvironmentField = processEnvironmentClass.getDeclaredField("theCaseInsensitiveEnvironment");
    theCaseInsensitiveEnvironmentField.setAccessible(true);
    Map<String, String> cienv = (Map<String, String>)     theCaseInsensitiveEnvironmentField.get(null);
    cienv.putAll(newenv);
  } catch (NoSuchFieldException e) {
    Class[] classes = Collections.class.getDeclaredClasses();
    Map<String, String> env = System.getenv();
    for(Class cl : classes) {
      if("java.util.Collections$UnmodifiableMap".equals(cl.getName())) {
        Field field = cl.getDeclaredField("m");
        field.setAccessible(true);
        Object obj = field.get(env);
        Map<String, String> map = (Map<String, String>) obj;
        map.clear();
        map.putAll(newenv);
      }
    }
  }
}

This Works like a charm. Full credits to the two authors of these hacks.

One way to do it is:

while read p; do
  echo "$p"
done <peptides.txt

As pointed out in the comments, this has the side effects of trimming leading whitespace, interpreting backslash sequences, and skipping the last line if it's missing a terminating linefeed. If these are concerns, you can do:

while IFS="" read -r p || [ -n "$p" ]
do
  printf '%s\n' "$p"
done < peptides.txt

Exceptionally, if the loop body may read from standard input, you can open the file using a different file descriptor:

while read -u 10 p; do
  ...
done 10<peptides.txt

Here, 10 is just an arbitrary number (different from 0, 1, 2).