Re: how to truncate an array

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

On Mar 4, 10:04am, Ray Andrews wrote:
}
} This should be dead simple, but I can't figure out how  to do it. I have 
} an array that can be
} arbitrarily long, and I want to truncate it at 20 elements.

Really an array?  Or a string you want to index by character?

    array[21,-1]=()
    string[21,-1]=''

}      setopt POSIX_STRINGS
}      string[20]='\0'

No, that inserted a literal backslash zero into the string.  You meant

    string[21]=$'\0'   # Zsh array indices start at 1, not at 0

but even that doesn't do what you intended because it doesn't actually
insert a NUL into the array, it just deletes the 21st character.
Assigning to string slices with subscript syntax causes the string to
act like an array.  Also, POSIX_STRINGS means that the string $'...'
ends at the NUL, so $'\0' and $'' and $'\0stuff' are all the same.

(Yes, you have C on the brain.  A shell array and a C array are only
loosely related; shell arrays behave more like linked lists.)

Even if it did insert a NUL into the array, the array would't really
be truncated, it's just that this:

}      echo "string is now truncated: $string"

would truncate the quoted portion at the NUL and not show you the rest
of the value of $string.

A side-effect of POSIX_STRINGS is that practically speaking the only
way to generate a NUL byte is to read one from an external program.