I want to learn to use the shell and was wondering why this …

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Author: Eric Andresen
Date:  
Subject: I want to learn to use the shell and was wondering why this didn't do as expected
Try: cat mypasswd |sort

On Thu, 2003-02-20 at 13:06, Michael Havens wrote:
> [bmike1@localhost training]$ head -20 /etc/passwd >mypasswd
>
> First I looked at what I had created.
>
> [bmike1@localhost training]$ more mypasswd
> root:x:0:0:root:/root:/bin/bash
> bin:x:1:1:bin:/bin:/bin/sh
> daemon:x:2:2:daemon:/sbin:/bin/sh
> adm:x:3:4:adm:/var/adm:/bin/sh
> lp:x:4:7:lp:/var/spool/lpd:/bin/sh
> sync:x:5:0:sync:/sbin:/bin/sync
> shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
> halt:x:7:0:halt:/sbin:/sbin/halt
> mail:x:8:12:mail:/var/spool/mail:/bin/sh
> news:x:9:13:news:/var/spool/news:/bin/sh
> uucp:x:10:14:uucp:/var/spool/uucp:/bin/sh
> operator:x:11:0:operator:/var:/bin/sh
> games:x:12:100:games:/usr/games:/bin/sh
> nobody:x:65534:65534:Nobody:/:/bin/sh
> rpm:x:13:104:system user for rpm:/var/lib/rpm:/bin/false
> vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
> xfs:x:70:70:system user for XFree86:/etc/X11/fs:/bin/false
> rpc:x:71:71:system user for portmap:/:/bin/false
> rpcuser:x:72:72:system user for nfs-utils:/var/lib/nfs:/bin/false
> postfix:x:73:73:system user for postfix:/var/spool/postfix:/bin/false
>
> Then I tried to sort it and look at the result.
>
> [bmike1@localhost training]$ sort mypasswd |cat mypasswd
> root:x:0:0:root:/root:/bin/bash
> bin:x:1:1:bin:/bin:/bin/sh
> daemon:x:2:2:daemon:/sbin:/bin/sh
> adm:x:3:4:adm:/var/adm:/bin/sh
> lp:x:4:7:lp:/var/spool/lpd:/bin/sh
> sync:x:5:0:sync:/sbin:/bin/sync
> shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
> halt:x:7:0:halt:/sbin:/sbin/halt
> mail:x:8:12:mail:/var/spool/mail:/bin/sh
> news:x:9:13:news:/var/spool/news:/bin/sh
> uucp:x:10:14:uucp:/var/spool/uucp:/bin/sh
> operator:x:11:0:operator:/var:/bin/sh
> games:x:12:100:games:/usr/games:/bin/sh
> nobody:x:65534:65534:Nobody:/:/bin/sh
> rpm:x:13:104:system user for rpm:/var/lib/rpm:/bin/false
> vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
> xfs:x:70:70:system user for XFree86:/etc/X11/fs:/bin/false
> rpc:x:71:71:system user for portmap:/:/bin/false
> rpcuser:x:72:72:system user for nfs-utils:/var/lib/nfs:/bin/false
> postfix:x:73:73:system user for postfix:/var/spool/postfix:/bin/false
>
> which I found was not sorted. So I thought that the sort had to be rewritten
> to the file and then I would look at it.
>
> [bmike1@localhost training]$ sort mypasswd >mypasswd |cat mypasswd
>
> which just returned the prompt. Did I erase it? let's look at it.
>
> [bmike1@localhost training]$ cat mypasswd
>
> which gave me the prompt again. Why did it do this?

--
--Eric Andresen