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Comment by LanternLight83 | Hacker News Reader

You can use brace expansion to avoid calling out to seq in a subshell (`{1..5}` expands to `1 2 3 4 5`)

Awesome, thanks!! Just found the section of the man page, looks like a pretty feature-filled expansion technique:

       A sequence expression takes the form {x..y[..incr]}, where x and y are either  integers  or
       single  characters, and incr, an optional increment, is an integer.  When integers are sup-
       plied, the expression expands to each number between x and y, inclusive.  Supplied integers
       may  be  prefixed  with  0  to  force each term to have the same width.  When either x or y
       begins with a zero, the shell attempts to force all generated terms  to  contain  the  same
       number  of digits, zero-padding where necessary.  When characters are supplied, the expres-
       sion expands to each character lexicographically between x  and  y,  inclusive,  using  the
       default  C locale.  Note that both x and y must be of the same type.  When the increment is
       supplied, it is used as the difference between each term.  The default increment is 1 or -1
       as appropriate.

...although I just tested it, and the increment and 0-padding only work in non-interactive mode ='(

> ...although I just tested it, and the increment and 0-padding only work in non-interactive mode ='(

Works for me...

    $ echo $0 # determine current shell (alternative: "ps -p $$")
    bash
    $ echo {01..100..20}
    001 021 041 061 081

But note that `{x..y}` has a major limitation: it doesn't support variables. Example:

    $ n=5
    $ echo {1..$n}
    {1..5}
    # intended output: 1 2 3 4 5

The `for ((...))` syntax mentioned by @zazaulola supports variables (it works in bash and zsh).

For completeness, here is a POSIX sh approach that doesn't require `seq` (in fact I notice this is what your "Uber Fancy" version uses internally):

    i=1
    while [ "$i" -le 5 ]; do
        echo "$i"
        i="$((i+1))"
    done

(but note that `continue` won't work properly).

Ahhh, my login shell is bash v3 (friggin' MacOS!) but my PATH has bash v5! On Bash v5 it works interactively! (probably v4+ too)

You can always do double eval for variables:

    var=1234
    echo `echo {1..$var}`

Yup, which you could also write as eval echo {1..$var} . The second argument's variable is being interpolated as if it's a quoted string, before it gets passed to eval, so eval is actually seeing "{1..1234}" and not doing the interpolation itself (because it wouldn't, because the variable isn't valid in a range). This should prevent the need for a subshell and the second echo call.

With an array:

  var=12
  declare -a array=()
  eval "array=( {01..$var} )"
  echo "${array[@]}"
  # 01 02 03 04 05 06 07 08 09 10 11 12

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