How to know if data is piped into my script

I have the following script:

-----
#!/usr/bin/perl

use strict;
use warnings;

my %hist = ();
my @hist;

$hist{(split /\s+/)[3]}++
foreach (`$ENV{'SHELL'} -c history`);

print map {"$hist{$_} : $_\n"}
sort {$hist{$b} <=> $hist{$a}}
keys %hist;
-----

I want to change it such that it uses '`$ENV{'SHELL'} -c history`'
only if nothing is piped into the script. If I call the script like:

% myscript.pl

It should use '`$ENV{'SHELL'} -c history`'. However if it is called
like:

% history | myscript.pl

It should use the piped in data instead.

What would be the best approach?

Thanks,
Mahesh

Re: How to know if data is piped into my script

Mahesh Asolkar wrote:
> I have the following script:
>
> -----
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> my %hist = ();
> my @hist;
>
> $hist{(split /\s+/)[3]}++
> foreach (`$ENV{'SHELL'} -c history`);
>
> print map {"$hist{$_} : $_\n"}
> sort {$hist{$b} <=> $hist{$a}}
> keys %hist;
> -----

Assuming it is safe to load all input into memory at once:

my @x=<>;
foreach (@x? @x : `$ENV{'SHELL'} -c history`) {

This will do what <> does, not just pipes. If you want only STDIN, and
only when STDIN is hooked up to a pipe, then maybe:

foreach (-p STDIN ? : `$ENV{'SHELL'} -c history`) {


Xho

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Re: How to know if data is piped into my script

Mahesh Asolkar wrote:
>
> It should use '`$ENV{'SHELL'} -c history`'. However if it is called
> like:
>
> % history | myscript.pl
>
> It should use the piped in data instead.

unless (-t) {
# STDIN is not opend to a tty but a file or pipe
}

Frank
--
Dipl.-Inform. Frank Seitz; http://www.fseitz.de/
Anwendungen für Ihr Internet und Intranet
Tel: 04103/180301; Fax: -02; Industriestr. 31, 22880 Wedel

Re: How to know if data is piped into my script

On Apr 15, 12:49=A0pm, Frank Seitz wrote:
> Mahesh Asolkar wrote:
>
> > It should use =A0'`$ENV{'SHELL'} -c history`'. However if it is called
> > like:
>
> > =A0 % history | myscript.pl
>
> > It should use the piped in data instead.
>
> unless (-t) {
> =A0 =A0 # STDIN is not opend to a tty but a file or pipe
>
> }
>

Thanks Frank and Xho. -t and -p do exactly what I was looking for.

Xho, I had tried the first way you suggested too. It works in the case
of 'history | myscript.pl', but it blocks 'myscript.pl' waiting for <>
to return.

Here's the script with the changes (I picked -p):

---------
#!/usr/bin/perl

use strict;
use warnings;

my %hist =3D ();
my @hist;

$hist{(split /\s+/)[3]}++
foreach ((-p STDIN) ? : `$ENV{'SHELL'} -c history`);

print map {"$hist{$_} : $_\n"}
sort {$hist{$b} <=3D> $hist{$a}}
keys %hist;
---------

/Mahesh

Re: How to know if data is piped into my script

Hi Makesh,


Small clarification.

-p checks whether input is a pipe
and "-p STDIN" would capture the case:

program | perlscript.pl


whereas -t CHECKS WHETHER input is a terminal.
so "unless -t STDIN" would also capture

perlscript.pl < filename


bye

N


Mahesh Asolkar wrote:
> On Apr 15, 12:49 pm, Frank Seitz wrote:
>> Mahesh Asolkar wrote:
>>
>>> It should use '`$ENV{'SHELL'} -c history`'. However if it is called
>>> like:
>>> % history | myscript.pl
>>> It should use the piped in data instead.
>> unless (-t) {
>> # STDIN is not opend to a tty but a file or pipe
>>
>> }
>>
>
> Thanks Frank and Xho. -t and -p do exactly what I was looking for.
>
> Xho, I had tried the first way you suggested too. It works in the case
> of 'history | myscript.pl', but it blocks 'myscript.pl' waiting for <>
> to return.
>
> Here's the script with the changes (I picked -p):
>
> ---------
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> my %hist = ();
> my @hist;
>
> $hist{(split /\s+/)[3]}++
> foreach ((-p STDIN) ? : `$ENV{'SHELL'} -c history`);
>
> print map {"$hist{$_} : $_\n"}
> sort {$hist{$b} <=> $hist{$a}}
> keys %hist;
> ---------
>
> /Mahesh