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user233233
Asked: 2014-01-12 06:48:50 +0800 CST

What's mean "identical to -e" when I use this command: ps -A?

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I want to know what this mean.

ps -A → Select all processes. Identical to -e.

What's mean "Identical to -e."?

ps

3 Answers

  1. It simply means that the command can be either typed as ps -A or ps -e and will produce the same result.

    • 4

  2. If means that 

    ps -A

    and

    ps -e

    are the same command.

    It is a compatibility issue: in older nonstandartized UNIX systems there were many implementations of commands, and sometimes they used different options for the same things.

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  3. From man ps:

       -A     Select all processes.  Identical to -e.

   [...]

   -e     Select all processes.  Identical to -A.

    So, these two options, -A and -e, are identical (equivalent) and produce identical results when these are used inside of ps command and their job is (no matter what option, -A or -e, you choose to use) to select all processes when ps is invoked.

    Now, what identical means? From http://dictionary.reference.com/browse/identical:

    1. similar or alike in every way: The two cars are identical except for their license plates.
    2. being the very same; selfsame: This is the identical room we stayed in last year.
    3. agreeing exactly: identical opinions.

    Synonyms: congruous, congruent, equal, matching.

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