CODEWITHSUNDEEP
perl
user354134
user354134

Reputation:

How to tell if my program is being piped to another (Perl)

"ls" behaves differently when its output is being piped: 

 
> ls ??? 
bar  foo 
> ls ??? | cat 
bar 
foo

How does it know, and how would I do this in Perl?

Upvotes: 12

Views: 221

Answers (2)

mob
mob

Reputation: 118665

In Perl, the -t file test operator indicates whether a filehandle (including STDIN) is connected to a terminal.

There is also the -p test operator to indicate whether a filehandle is attached to a pipe.

$ perl -e 'printf "term:%d, pipe:%d\n", -t STDIN, -p STDIN'
term:1, pipe:0
$ perl -e 'printf "term:%d, pipe:%d\n", -t STDIN, -p STDIN' < /tmp/foo
term:0, pipe:0
$ echo foo | perl -e 'printf "term:%d, pipe:%d\n", -t STDIN, -p STDIN'
term:0, pipe:1

File test operator documentation at perldoc -f -X.

Upvotes: 13

mpapec
mpapec

Reputation: 50667

use IO::Interactive qw(is_interactive);

is_interactive() or warn "Being piped\n";

Upvotes: 6

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