Re: posix ps (was Re: Adding `pgrep' and `pkill' to /usr/bin)

From: Albert Cahalan (albert_at_users.sf.net)
Date: 03/29/04

  • Next message: Garance A Drosihn: "Re: posix ps (was Re: Adding `pgrep' and `pkill' to /usr/bin)" 
    To: Stephen McKay <smckay@internode.on.net>
Date: 28 Mar 2004 20:23:56 -0500

    On Sun, 2004-03-28 at 19:42, Stephen McKay wrote:
    > On Sunday, 28th March 2004, Harti Brandt wrote:
    >
    > >Well, that is just like LANG or LC_ALL. You cannot depend on parsing
    > >utility output until you set LC_ALL=C, yet I have still to see a script
    > >that does this.
    >
    > Yes, that is a significant deficiency of the internationalisation scheme.
    > That doesn't mean we should copy it though.

    At least this is proof that the idea is nothing crazy.
    It has problems, but then so does everything else.

    > >If you happen to write a script for BSD syntax just put LC_ALL=C
    > >PERSONALITY=BSD on top of it.
    >
    > Hopefully in the near future there will be a universally accepted default
    > for ps options. Are you seriously suggesting that every script forevermore
    > will have to put PERSONALITY=STANDARD (or similar) in front of a two
    > character command name just to defeat this misfeature?

    Generally, no. You set the personality when you run
    a large, complicated, or read-only script that expects
    some non-default behavior.

    The man page can document that "stuff may break".
    Users, especially those not doing sysadmin work,
    are free to take that risk.

    Personality support is a compatibility hack. You use
    it to make stuff work, not to break things.

    > >SM>If multiple personalities is a desirable trait (and it's not clear that it
    > >SM>is) then command line switches and aliases are the correct mechanisms to
    > >SM>use.
    > >
    > >That would require to add that switch to all utility calls in a script
    > >that have multiple personalities. Thats far from being desirable.
    >
    > I don't understand. I was suggesting that if end users want different
    > flavours of output they can select them with command line switches and
    > aliases (if this is an option at all). This is as opposed to allowing
    > users to select the default via an environment variable, which would
    > negatively impact the use of ps in scripts.

    You have that flipped around. Personality support allows
    you to make your old or foreign-OS scripts work.

    If you're porting something big, throwing CMD_ENV=sysv or
    CMD_ENV=bsd at the top may be the the most expedient way
    to deal with things. This is especially true if you're
    dealing with a commercial package designed for another OS.

    > I can't see why scripts would want to use anything but the standard options.
    > You only want to parse one format.

    Basic multi-personality support is not difficult.
    I'll call this semi-auto mode. Tru64 and AIX do this.
    If CMD_ENV=bsd is set or the first option lacks a hyphen,
    you parse in BSD mode. Every option goes through the
    bsd switch() table. If CMD_ENV=sysv is set and the
    first option has a hyphen, every option goes through
    the sysv switch table.

    You can get fancy. There are some tricks to make a
    transition easier or more useful. For example, Linux
    ps will give a warning and fall back to BSD mode if
    the UNIX-style parser encounters problems. You can
    allow mixed options; my users really like this.

    I'll end with a chunk of my man page. Please note the comment
    "In general, it is a bad idea to set these variables." applying
    to all environment variables (not just personality) and the
    fact that the 4 non-POSIX personalities are marked with the
    comment "(totally non-standard)" to warn the users.

    --------------------------------------------------------------------
    ENVIRONMENT VARIABLES
    The following environment variables could affect ps:
        COLUMNS Override default display width.
        LINES Override default display height.
        PS_PERSONALITY Set to one of posix,old,linux,bsd,sun,digital...
        CMD_ENV Set to one of posix,old,linux,bsd,sun,digital...
        I_WANT_A_BROKEN_PS Force obsolete command line interpretation.
        LC_TIME Date format.
        PS_COLORS Not currently supported.
        PS_FORMAT Default output format override.
        PS_SYSMAP Default namelist (System.map) location.
        PS_SYSTEM_MAP Default namelist (System.map) location.
        POSIXLY_CORRECT Don't find excuses to ignore bad "features".
        UNIX95 Don't find excuses to ignore bad "features".
        _XPG Cancel CMD_ENV=irix non-standard behavior.

    In general, it is a bad idea to set these variables. The one exception
    is CMD_ENV or PS_PERSONALITY, which could be set to Linux for normal
    systems. Without that setting, ps follows the useless and bad parts
    of the Unix98 standard.

    PERSONALITY
        390 like the S/390 OpenEdition ps
        aix like AIX ps
        bsd like FreeBSD ps (totally non-standard)
        compaq like Digital Unix ps
        debian like the old Debian ps
        digital like Digital Unix ps
        gnu like the old Debian ps
        hp like HP-UX ps
        hpux like HP-UX ps
        irix like Irix ps
        linux ***** RECOMMENDED *****
        old like the original Linux ps (totally non-standard)
        posix standard
        sco like SCO ps
        sgi like Irix ps
        sun like SunOS 4 ps (totally non-standard)
        sunos like SunOS 4 ps (totally non-standard)
        sysv standard
        unix standard
        unix95 standard
        unix98 standard

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