Shell – How to read from a pipe keeping positional parameters

POSIXly, the parsing for options should stop at -- or at the first non-option (or non-option-argument) argument whichever comes first. So in

cp -R file1 -t /mybackup file2 -f

that's at file1, so cp should recursively copy all of file1, -t, /mybackup and file2 into the -f directory.

GNU getopt(3) however (that GNU cp uses to parse options (and here you're using GNU cp since you're using the GNU-specific -t option)), unless the $POSIXLY_CORRECT environment variable is set, accepts options after arguments. So it is actually equivalent to POSIX option style parsing's:

cp -R -t /mybackup -f -- file1 file2

The getopts shell built-in, even in the GNU shell (bash) only handles the POSIX style. It also doesn't support long options or options with optional arguments.

If you want to parse the options the same way as GNU cp does, you'll need to use the GNU getopt(3) API. For that, if on Linux, you can use the enhanced getopt utility from util-linux (that enhanced version of the getopt command has also been ported to some other Unices like FreeBSD).

That getopt will rearrange the options in a canonical way which allows you to parse it simply with a while/case loop.

$ getopt -n "$0" -o t:Rf -- -Rf file1 -t/mybackup file2
 -R -f -t '/mybackup' -- 'file1' 'file2'

You'd typically use it as:

parsed_options=$(
  getopt -n "$0" -o t:Rf -- "$@"
) || exit
eval "set -- $parsed_options"
while [ "$#" -gt 0 ]; do
  case $1 in
    (-[Rf]) shift;;
    (-t) shift 2;;
    (--) shift; break;;
    (*) exit 1 # should never be reached.
  esac
done
echo "Now, the arguments are $*"

Also note that that getopt will parse options the same way as GNU cp does. In particular, it supports the long options (and entering them abbreviated) and honours the $POSIXLY_CORRECT environment variables (which when set disables support for options after arguments) the same way GNU cp does.

Note that using gdb and printing the arguments that getopt_long() receives can help building the parameters to getopt(1):

(gdb) bt
#0  getopt_long (argc=2, argv=0x7fffffffdae8, options=0x4171a6 "abdfHilLnprst:uvxPRS:T", long_options=0x417c20, opt_index=0x0) at getopt1.c:64
(gdb) set print pretty on
(gdb) p *long_options@40
$10 = {{
    name = 0x4171fb "archive",
    has_arg = 0,
    flag = 0x0,
    val = 97
  }, {
    name = 0x417203 "attributes-only",
[...]

Then you can use getopt as:

getopt -n cp -o abdfHilLnprst:uvxPRS:T -l archive... -- "$@"

Remember that GNU cp's list of supported options may change from one version to the next and that getopt will not be able to check if you pass a legal value to the --sparse option for instance.

Instead of a temporary file, you could use of your shell's support for process substitution (this assumes bash, zsh or some implementations of ksh (the feature was introduced by ksh88)):

awk -f ./script.awk <(cat file.txt)

This will provide awk a file name in place of the <(...) construct which, when read, will contain the output of the enclosed command.