PERL Beginners

Author

rameshbabu

2006-06-27, 7:58 am

hi all,
can any body tell me what is a pipe .......in detail ....and
wat does this mean
open (MYPIPE, "| cat >hello");

Thanks

From
Ramesh

boyd

2006-06-27, 7:58 am

In article <1151414103.644247.236050@75g2000cwc.googlegroups.com>,
"rameshbabu" <bhupal78999@gmail.com> wrote:

> hi all,
> can any body tell me what is a pipe .......in detail ....and
> wat does this mean
> open (MYPIPE, "| cat >hello");
>
> Thanks
>
> From
> Ramesh

The simple answer is: a pipe connects two processes together - it
"pipes" the stdout output from the first command to the stdin input of
the second command.

So from the command line, if you enter:
echo "Hi there" | cat > hello
that will pipe the output from echo, "Hi there" to cat which will, in
turn, create a file called 'hello' with the contents "Hi there".

In your example, you are creating a file called "hello", and anything
you print to MYPIPE will be inserted into that file.

It would be equivalent to:

open( MYPIPE, ">hello" )

in effect. The difference is that the pipe starts another process "cat"
to do the actual writing to the file.

You can read about pipes in these manual pages: (look for 'pipeline' )
man sh
man csh
man bash
or in any Unix introduction.

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