Bash – How to match name exactly with Bash’s `help` builtin

You can tell GNU sed to read the script from standard input with -f -, -f meaning to read the script from a file, and - meaning standard input as is common with a lot of commands.

sed -f - "$IN" > "$OUT" << SED_SCRIPT
    s/a/1/g
    s/test/full/g
SED_SCRIPT

POSIX sed also supports -f, but the use of - for standard input is not documented. In this case, you could use /dev/stdin on Linux systems (and I seem to recall Solaris has this too, but I cannot confirm that right now)

Using <<-SED_SCRIPT (with the '-' prefix) will allow the closing SED_SCRIPT tag to be indented.

From the section of execute_cmd.c of bash-4.2+dfsg that deals with TIMEFORMAT:

if (*s == 'R' || *s == 'E')
  len = mkfmt (ts, prec, lng, rs, rsf);
else if (*s == 'U')
  len = mkfmt (ts, prec, lng, us, usf);
else if (*s == 'S')
  len = mkfmt (ts, prec, lng, ss, ssf);
else
  {
    internal_error (_("TIMEFORMAT: `%c': invalid format character"), *s);
    free (str);
    return;
  }

So, from the above, it appears that %E means the same as %R: elapsed (real) time.

I have seen something similar in GNU sed. The -r option is documented as enabling sed's extended regular expressions. An undocumented feature is that -E does the same thing. In this case, the purpose is clear: this provides compatibility with the flag that BSD sed uses for extended regex. One possible reason for keeping it undocumented would be that it allows GNU the option to use -E for something else in the future. The reasons for allowing %E in TIMEFORMAT but keeping it undocumented might be similar.