Try exporting function, then calling it in a subshell:

showword() {
  echo $1
}

export -f showword
echo This is a sample message | xargs -d' ' -t -n1 -P2 bash -c 'showword "$@"' _

The function will get all the arguments passed to the bash command, but starting form 0, so, inside the function $0 would be _ and $1 would be next argument. See the link in the second comment.

Try exporting the function, then calling it in a subshell:

showword() {
  echo $1
}

export -f showword
echo This is a sample message | xargs -d' ' -t -n1 -P2 bash -c 'showword "$@"' _

This causes xargs to execute

bash -c 'showword "$@"' _ This
bash -c 'showword "$@"' _ is
bash -c 'showword "$@"' _ a
            ︙

The arguments passed to the bash command are, well, passed into the bash environment, but starting from 0.  So, inside the function,

• $0 is “_” and $1 is “This”
• $0 is “_” and $1 is “is”
• $0 is “_” and $1 is “a”
• ︙

See Bash -c with positional parameters.

Note that export -f works only in Bash, and -Pn (--max-procs=max-procs) works only in GNU xargs.

Try exporting function, then calling it in a subshell:

showword() {
  echo $1
}

export -f showword
echo This is a sample message | xargs -d' ' -t -n1 -P2 bash -c 'showword "$@"' _

Try exporting function, then calling it in a subshell:

showword() {
  echo $1
}

export -f showword
echo This is a sample message | xargs -d' ' -t -n1 -P2 bash -c 'showword "$@"' _

The function will get all the arguments passed to the bash command, but starting form 0, so, inside the function $0 would be _ and $1 would be next argument. See the link in the second comment.