Bash – Split string by space in ZSH

arraybashreadzsh

Give this file.txt:

first line
second line
third line

This works in bash:

while IFS=' ' read -a args; do
  echo "${args[0]}"
done < file.txt

To produce

first
second
third

That is to say, we were able to read the file line by line, and on each one we split the line further into an array using space as a delimiter. But in zsh, the result is an error: read: bad option: -a.

How can we achieve in zsh the same as in bash? I’ve tried several solutions, but I was never able to split a string into an array using spaces as the delimiter.

Best Answer

From man zshbuiltins, zsh's read uses -A instead.

read [ -rszpqAclneE ] [ -t [ num ] ] [ -k [ num ] ] [ -d delim ]
     [ -u n ] [ name[?prompt] ] [ name ...  ]
...
       -A     The  first  name  is taken as the name of an array
              and all words are assigned to it.

Hence the command is

while IFS=' ' read -A args; do
  echo "${args[1]}"
done < file.txt

N.B. by default, zsh array numbering begins with 1, whereas bash's begins with 0.

$ man zshparam
...
Array Subscripts
...
The elements are numbered  beginning  with  1, unless the
KSH_ARRAYS option is set in which case they are numbered from zero.

Related Solutions

Zsh – How to Collect an Array of Lines Properly

TL, DR:

array_of_lines=("${(@f)$(my_command)}")

First mistake (→ Q2): IFS='\n' sets IFS to the two characters \ and n. To set IFS to a newline, use IFS=$'\n'.

Second mistake: to set a variable to an array value, you need parentheses around the elements: array_of_lines=(foo bar).

This would work, except that it strips empty lines, because consecutive whitespace counts as a single separator:

IFS=$'\n' array_of_lines=($(my_command))

You can retain the empty lines except at the very end by doubling the whitespace character in IFS:

IFS=$'\n\n' array_of_lines=($(my_command))

To keep trailing empty lines as well, you'd have to add something to the command's output, because this happens in the command substitution itself, not from parsing it.

IFS=$'\n\n' array_of_lines=($(my_command; echo .)); unset 'array_of_lines[-1]'

(assuming the output of my_command doesn't end in a non-delimited line; also note that you lose the exit status of my_command)

Note that all the snippets above leave IFS with its non-default value, so they may mess up subsequent code. To keep the setting of IFS local, put the whole thing into a function where you declare IFS local (here also taking care of preserving the command's exit status):

collect_lines() {
  local IFS=$'\n\n' ret
  array_of_lines=($("$@"; ret=$?; echo .; exit $ret))
  ret=$?
  unset 'array_of_lines[-1]'
  return $ret
}
collect_lines my_command

But I recommend not to mess with IFS; instead, use the f expansion flag to split on newlines (→ Q1):

array_of_lines=("${(@f)$(my_command)}")

Or to preserve trailing empty lines:

array_of_lines=("${(@f)$(my_command; echo .)}")
unset 'array_of_lines[-1]'

The value of IFS doesn't matter there. I suspect that you used a command that splits on IFS to print $array_of_lines in your tests (→ Q3).

Bash: split multi line input into array

Your attempt is close to the actual solution. The relevant flag can be found in the read help:

$ help read
...
      -d delim  continue until the first character of DELIM is read, rather
            than newline

It doesn't explicitly mention it, but you can set the delimiter to empty, and thus it'll read until EOF.

$ IFS=, read -d '' -a myarray < myfile

$ echo ${myarray[2]}
U2FsdGVkX1/c8rTTO41zVT7gB+KL+n7KoNCgM3vfchOyuvBngdXDGjXTvXTK0jz6

Best Answer

Related Solutions

Zsh – How to Collect an Array of Lines Properly

Bash: split multi line input into array

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