Why does read -a fail in zsh

Question

If I type:

echo "1 the
dquote> 2 quick
dquote> 3 brown" | while read -a D; do echo "${D[1]}--${D[0]}"; done

in bash it says:

the--1
quick--2
brown--3

but in zsh it says:

zsh: bad option: -a

Why? And what should I do instead?

Answer 1

In both shells read is a builtin. It shares the same purpose, but the implementation and options differ.

In order to read in an array in zsh, read requires the option -A (instead of -a):

echo "1 the
2 quick   
3 brown" | while read -A D; do echo $D[2]--$D[1]; done 

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Note: There are many more differences between zsh and bash:

• In zsh arrays are numbered from one by default, in bash they start from zero.
• echo $ARRAY prints outputs all elements in zsh but only the first element in bash
• To print the third element of an array in sh you can use echo $ARRAY[3]. In bash braces are needed to delimit the subscript, also the subscript for the third element is 2: echo ${ARRAY[2]}.

• In zsh you usually do not need to quote parameter expansions in order to handle values with white spaces correctly. For example

  FILENAME="no such file"
  cat $FILENAME
  

  will print only one error message in zsh:

  cat: 'no such file': No such file or directory
  

  but three error messages in bash:

  cat: no: No such file or directory
  cat: such: No such file or directory
  cat: file: No such file or directory
  

• In zsh the builtin echo evaluates escape codes by default. In bash you need to pass the -e argument for that.

  echo 'foo\tbar'
  

  zsh:

  foo     bar
  

  bash:

  foo\tbar
  

• …

Generally, it is important to keep in mind that, while zsh and bash are similar, they are far from being the same.