bash标志，可选从stdin或文件中读取

Question

I know this is probably a stupid question but it has me stumped. I'm trying to write a shell script that accepts flags, and one optional variable. A file. If a file is passed, it reads from the file. If not, It reads from stdin. I know similar questions have been asked, but I can't find an answer to my specific question.

I've provided an example below that illustrates the issue. I've left some parts out (such as validation) for brevity's sake.

I can accept flags and read from a file. OR I can optionally accept a variable (file) and read from the file. If no file is passed, then we read from stdin. For some reason, when I try to combine the two (accept flags, read optional file defaulting to stdin) I get an error.

This works.

#!/bin/sh
set -eu

while IFS=, read -r f1 
do
  echo $f1
done <"${1:-/dev/stdin}"

I can call it like this... ./test.sh <<< "testing123" or this... echo "testing123" | ./test.sh echo "testing123" | ./test.sh or this... ./test.sh foo.csv . All return testing123 assuming that foo.csv contains testing123 .

This Also Works.

#!/bin/sh
set -eu

while true
do
  case $1 in
    -h|--help)
      echo "-h"
      exit
      ;;
    --)
      shift
      break
      ;;
    -?*)
      echo "unknown"
      ;;
    *)
      break
  esac

  shift
done

while IFS=, read -r f1 
do
  echo $f1
done <"${1}"

I can call it like this ./test.sh foo.csv or this ./test.sh -f foo.csv . The first case returns testing123 and the second case returns

unknown
testing123

For some reason, this doesn't work. I don't understand what I'm missing here?

#!/bin/sh
set -eu

while true
do
  case $1 in
    -h|--help)
      echo "-h"
      exit
      ;;
    --)
      shift
      break
      ;;
    -?*)
      echo "unknown"
      ;;
    *)
      break
  esac

  shift
done

while IFS=, read -r f1 
do
  echo $f1
done <"${1:-/dev/stdin}"

Called like this ./test foo.csv it returns testing123 . Called like this ./test -f foo.csv it returns

unknown
testing123

Called like this:

echo "testing123" | ./test.sh

or this

./test.sh <<< "testing123"

it returns

./test.sh: line 6: $1 unbound variable

Answer 1

Change

while true

to

while [ $# -ne 0 ]

When you run out of arguments, your code continues with the next iteration of the loop, and tries to test $1 , which doesn't exist. Since you have done set -eu , referencing an unset variable causes an error and the script aborts.