Question

#! /bin/bash
if [ $1 ]; then
  redirect="<"$1
else
  redirect="<&0"
fi
mysql --host=a.b --port=3306 --user=me --password='!' -D DCVBase2 $redirect

wanna redirect from either file or stdin. May be use some quatation around $redirect?

Answer 1

You can’t put the “<…” in a variable, but you can put the parameter to it in a variable

Also, redirecting stdin from /dev/fd/0 is a no-op, because /dev/fd/0 is bash’s stdin, which is what mysql would inherit by default.

so you can make this work by falling back to taking stdin from /dev/fd/0, which looks similar to James_R_Ferguson’s answer, except that it uses /dev/fd/0 because using /dev/tty makes an assumption that bash’s stdin is an actual terminal.

#! /bin/bash

if [ -n "$1" ]; then # note, I changed this to test for non-empty
  redirect="$1"
else
  redirect="/dev/fd/0"
fi3
mysql --host=a.b --port=3306 --user=me --password='!' -D DCVBase2 < "$redirect"