Shell script - is this expected behaviour?

Shell script - is this expected behaviour?

[Gary]

If I have a shell script which reads a file which does not have an end
of line character at the end if it's only line, it does not read
anything.

For example:
,----
| #!/bin/sh
| 
| fileName="test.xml"
| retVal="Z"
| 
| exec 10<&0
| exec < $fileName
| while read configLine
| do
|     retVal="A"
| done
| exec 0<&10 10<&-
| 
| echo $retVal
| 
| exit 0
`----

If it's expected behaviour, what's the workaround?

-- 
Gary        Please do NOT send me 'courtesy' replies off-list.


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Re: Shell script - is this expected behaviour?

[Eric Blake]

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On 11/29/2011 02:00 AM, Gary wrote:
> If I have a shell script which reads a file which does not have an end
> of line character at the end if it's only line, it does not read
> anything.

Not cygwin specific.

> 
> For example:
> ,----
> | #!/bin/sh
> | 
> | fileName="test.xml"

Your example didn't tell us the contents of test.xml.  But this is
reproducible even without knowing the contents of test.xml.

> | retVal="Z"
> | 
> | exec 10<&0
> | exec < $fileName
> | while read configLine

read(1) is required to return non-zero status when it encounters a
partial line (one with no end of line character).  Which means that
since testXML had no newline character, read never returned status 0,
which means you never entered the body of the while loop,

> | do
> |     retVal="A"

which means retVal was never assigned.

> | done
> | exec 0<&10 10<&-
> | 
> | echo $retVal

So this is echoing an unassigned variable, as required by POSIX.

> | 
> | exit 0
> `----
> 
> If it's expected behaviour, what's the workaround?

Never feed 'read' unterminated input.  Always end your text files with a
newline.

-- 
Eric Blake   eblake@redhat.com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: Shell script - is this expected behaviour?

[Gary]

Eric Blake wrote:
> On 11/29/2011 02:00 AM, Gary wrote:
>> If I have a shell script which reads a file which does not have an end
>> of line character at the end if it's only line, it does not read
>> anything.
>
> Not cygwin specific.

Okay, thanks. That's what I was wondering.

>> If it's expected behaviour, what's the workaround?
>
> Never feed 'read' unterminated input.  Always end your text files with a
> newline.

Yeah, sadly the input file isn't under my control. I ended up just
stuffing a newline on the end regardless. I would read the file first to
find out if it was necessary, but...

-- 
Gary        Please do NOT send me 'courtesy' replies off-list.


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RE: Shell script - is this expected behaviour?

[Nellis, Kenneth]

From: Eric Blake [mailto:eblake@redhat.com] 
Subject: Re: Shell script - is this expected behaviour?

> On 11/29/2011 02:00 AM, Gary wrote:
> > If I have a shell script which reads a file which does not have an
end
> > of line character at the end if it's only line, it does not read
> > anything.

<snip>

> Never feed 'read' unterminated input.  Always end your text files with
a
> newline.

When I can't control the contents of the input file, I pipe it through
a filter program I wrote that adds a final newline where the last
character of a stream is not a newline.
--Ken Nellis

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RE: Shell script - is this expected behaviour?

[Tim McDaniel]

Nellis, Kenneth wrote:
> From: Eric Blake 
>> Never feed 'read' unterminated input.  Always end your text files
>> with a newline.
>
> When I can't control the contents of the input file, I pipe it
> through a filter program I wrote that adds a final newline where the
> last character of a stream is not a newline.

I don't have the time to experiment at the moment, but I'm pretty sure
that some of the standard tools append a line terminator if it's not
already on the last line of their input.  sed or awk or gawk, maybe?
Anyway, if you can stumble on such a program, it can save you having
to write and maintain and distribute a filter to all your
environments.

-- 
Tim McDaniel

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Re: Shell script - is this expected behaviour?

[DSB]

On Tue, Nov 29, 2011 at 3:15 PM, Tim McDaniel <tmcd@panix.com> wrote:
> I don't have the time to experiment at the moment...

Likewise, but it seems likely some existing utilities like "line" or
"head -n1" might do the job. E.g.

foo=$(line < file)
foo=$(head -n1 file)

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RE: Shell script - is this expected behaviour?

[Nellis, Kenneth]

From: Tim McDaniel
Subject: RE: Shell script - is this expected behaviour?

>I don't have the time to experiment at the moment, but I'm pretty sure
>that some of the standard tools append a line terminator if it's not
>already on the last line of their input.  sed or awk or gawk, maybe?
>Anyway, if you can stumble on such a program, it can save you having
>to write and maintain and distribute a filter to all your
>environments.

FWIW, "grep ^" seems to do the trick.
--Ken Nellis

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Re: Shell script - is this expected behaviour?

[Fergus]

 >> Never feed 'read' unterminated input. Always end your text files 
with a newline.

Yay.
Please could /etc/setup/timestamp be terminated?
Currently it is not, causing minor grief e.g. when using a shell script 
to check for updates.
Fergus


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