Похоже, вам нужно регулярное выражение. Строка '$iperf' не существует в ваших данных, поэтому я предполагаю, что вы имеете в виду 'iperf'. Вы можете найти строки, содержащие эту строку, зацикливая файл по одной строке за раз и проверяя каждую строку регулярным выражением Если регулярное выражение выполнено успешно, вы можете напечатать строку.
#!/usr/bin/perl
use strict;
use warnings;
while (<DATA>) {
print if /\biperf\b/;
}
__DATA__
$iperf -c 172.29.38.67 -m -M 64 -i 5 -t 20 -P 10
WARNING: attempt to set TCP maximum segment size to 64, but got 536
WARNING: attempt to set TCP maximum segment size to 64, but got 536
WARNING: attempt to set TCP maximum segment size to 64, but got 536
WARNING: attempt to set TCP maximum segment size to 64, but got 536
WARNING: attempt to set TCP maximum segment size to 64, but got 536
WARNING: attempt to set TCP maximum segment size to 64, but got 536
WARNING: attempt to set TCP maximum segment size to 64, but got 536
WARNING: attempt to set TCP maximum segment size to 64, but got 536
WARNING: attempt to set TCP maximum segment size to 64, but got 536
WARNING: attempt to set TCP maximum segment size to 64, but got 536
------------------------------------------------------------
~ $ iperf -c 172.29.38.67 -m -M 128 -i 5 -t 20 -P 10
WARNING: attempt to set TCP maximum segment size to 128, but got 536
WARNING: attempt to set TCP maximum segment size to 128, but got 536
WARNING: attempt to set TCP maximum segment size to 128, but got 536
WARNING: attempt to set TCP maximum segment size to 128, but got 536
WARNING: attempt to set TCP maximum segment size to 128, but got 536
WARNING: attempt to set TCP maximum segment size to 128, but got 536
WARNING: attempt to set TCP maximum segment size to 128, but got 536
WARNING: attempt to set TCP maximum segment size to 128, but got 536
WARNING: attempt to set TCP maximum segment size to 128, but got 536
WARNING: attempt to set TCP maximum segment size to 128, but got 536
------------------------------------------------------------
Client connecting to 172.29.38.67, TCP port 5001
TCP window size: 16.0 KByte (default)
------------------------------------------------------------