'Re: [ast-users] Raw command substitution "$()"'

[prev in list] [next in list] [prev in thread] [next in thread] 

List:       ast-users
Subject:    Re: [ast-users] Raw command substitution "$()"
From:       Icarus Sparry <i.sparry+astuser () gmail ! com>
Date:       2013-12-16 21:42:11
Message-ID: 52AF73B3.70301 () gmail ! com
[Download RAW message or body]

[Attachment #2 (multipart/alternative)]

On 12/16/2013 1:02 PM, Eugene Schulman (BLOOMBERG/ 120 PARK) wrote:
> Hi guys,
> I'm looking for a method to do raw command substitution.
>
> The issue:
> - Need a ksh93t+ / ksh93u facillity to be able to take the literal
> output of a command with no substitutions or omissions, where the
> substitute data is less than 1kB. Target platforms are RHEL 6.4,
> Solaris 11 & AIX 7.1.
>
> Examples. printf is used below for illustration only.
> - $(), command substitution, i.e. FOO=$(printf "\n\n\n\n\n"); seems
> unsuitable as it modifies the output by performing some whitespace
> handling, such as stripping newlines. In this example, FOO returns
> zero-length.
> - "$()", quoted, prevents the field splitting and pathname expansions,
> but doesn't protect the trailing whitespace.
> - Binary read, i.e. printf "\n\n\n\n\n" | read -N$length FOO; works
> provided the $length of the read doesn't encounter the EOF, in this
> case values 1-5. If $length>5, in this example, FOO becomes
> zero-length. For an input of unknown length, this feels impractical.
> - One possible workaround is adding a suffix and then chopping it,
> i.e. FOO="$(printf "\n\n\n\n\nmysuffix")"; FOO="${FOO%mysuffix}"
>
>
The "possible workaround" is the normal approach, in my experience the
"mysuffix" is often just a single period or lower case x.

FOO=$(printf "\n\n\n" ; printf x ;) ; FOO=${FOO%x}

You can use 'echo x' rather than 'printf x' as the trailing newline that
echo produces will be removed by the command substitution.

[Attachment #5 (text/html)]

<html>
  <head>
    <meta content="text/html; charset=ISO-8859-1"
      http-equiv="Content-Type">
  </head>
  <body text="#000000" bgcolor="#FFFFFF">
    <div class="moz-cite-prefix">On 12/16/2013 1:02 PM, Eugene Schulman
      (BLOOMBERG/ 120 PARK) wrote:<br>
    </div>
    <blockquote cite="mid:52AF6A4901F6079C00390AE9_0_89941@p057"
      type="cite">
      <title></title>
      <!-- rte-version 0.2 9947551637294008b77bce25eb683dac -->
      <div class="rte-style-maintainer" style="font-family: Arial,
        'BB.Proportional'; white-space: pre-wrap; font-size: small;"
        data-color="global-default" data-bb-font-size="medium">Hi guys,
        <div>I'm looking for a method to do raw command substitution.</div>
        <div><br>
        </div>
        <div>
          <div>The issue:</div>
          <div>- Need a ksh93t+ / ksh93u facillity to be able to take
            the literal output of a command with no substitutions or
            omissions, where the substitute data is less than 1kB.
            Target platforms are RHEL 6.4, Solaris 11 &amp; AIX 7.1.</div>
          <div><br>
          </div>
          <div>Examples. printf is used below for illustration only.</div>
          <div>- $(), command substitution, i.e. FOO=$(printf
            "\n\n\n\n\n"); seems unsuitable as it modifies the output by
            performing some whitespace handling, such as stripping
            newlines. In this example, FOO returns zero-length.</div>
        </div>
        <div>- "$()", quoted, prevents the field splitting and pathname
          expansions, but doesn't protect the trailing whitespace.</div>
        <div>- Binary read, i.e. printf "\n\n\n\n\n" | read -N$length
          FOO; works provided the $length of the read doesn't encounter
          the EOF, in this case values 1-5. If $length&gt;5, in this
          example, FOO becomes zero-length. For an input of unknown
          length, this feels impractical.</div>
        <div>- One possible workaround is adding a suffix and then
          chopping it, i.e. FOO="$(printf "\n\n\n\n\nmysuffix")";
          FOO="${FOO%mysuffix}"</div>
        <div><br>
        </div>
        <br>
      </div>
    </blockquote>
    The "possible workaround" is the normal approach, in my experience
    the "mysuffix" is often just a single period or lower case x.<br>
    <br>
    FOO=$(printf "\n\n\n" ; printf x ;) ; FOO=${FOO%x}<br>
    <br>
    You can use 'echo x' rather than 'printf x' as the trailing newline
    that echo produces will be removed by the command substitution.<br>
    <br>
    <br>
    <br>
    <br>
    <br>
  </body>
</html>

_______________________________________________
ast-users mailing list
ast-users@lists.research.att.com
http://lists.research.att.com/mailman/listinfo/ast-users

[prev in list] [next in list] [prev in thread] [next in thread] 