STDIN from bash to perl script

Question

i have a perl script(myscript.pl)

use strict;
use IO::Handle;

open OUTPUT, '>', "output.txt" or die $!;

STDOUT->fdopen( \*OUTPUT, 'w' ) or die $!;

while (<STDIN>){
print $_;
}

i can paste into output.txt what i write on commandline

also

I have a bash script:

cat >in.$$ 

cat in.$$> /tmp/msg

i can paste what i have in in.$$ into /tmp/msg

i need to run perl script with stdin that come from bash script.

is it possible and how?

i tried , even though i know it is too silly

cat in.$$> ./myscript.pl
in.$$> ./myscript.pl
in.$$> perl myscript.pl

I probably have misunderstood it, but, how about ./myscript.pl in.$$? — Birei
– Birei, Commented Dec 5, 2013 at 16:41

mob · Accepted Answer · 2013-12-05 16:43:34Z

5

To specify the contents of a file as standard input to a bash command, use <

./myscript.pl < in.$$

To use the output of one command as the input to another command, use '|' (the 'pipe' character, as if you were sending bits from one process to another through a pipe)

cat in.$$ | ./myscript.pl
echo foo | ./myscript.pl

answered Dec 5, 2013 at 16:43

mob

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Comments

David W. · Accepted Answer · 2013-12-05 17:30:50Z

In your Perl script, use the diamond operator (aka the null file handle):

The null filehandle <> is special: it can be used to emulate the behavior of sed and awk, and any other Unix filter program that takes a list of filenames, doing the same to each line of input from all of them. Input from <> comes either from standard input, or from each file listed on the command line. Here's how it works: the first time <> is evaluated, the @ARGV array is checked, and if it is empty, $ARGV[0] is set to "-", which when opened gives you standard input. The @ARGV array is then processed as a list of filenames.

Here's an example:

#! /usr/bin/perl
# cat command emulator

while ( my $line = <> ) {
    chomp $line;
    say $line;
}

The <> will take each file listed on the command line, open them sequentially, and then read each line, or pull lines in from STDIN.

You can also do this:

while ( my $line = <STDIN> ) {
    chomp $line;
    say $line;
}

Which will read in lines from STDIN, but won't read files from the command line.

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