I got log file that can be up to 5 GB. And for processing it grep/sed commands are used. And I'm worried about how much pressure exerted on HDD? E.g if 500-1000 commands will be executed every hour could they kill my hard drive soon?
No. Most of the log read/writes would probably be done on the HD's cache anyway.
Hard drive vendors publish specs about such things. For example a Western Digital spec sheet shows the WD Black line of drives is rated for 300,000 Load/Unload cycles. A util like
smartctl will show a drive's current cycle count, so the user may compare the spec number to their own drive:
smartctl -a /dev/sda | grep Cycle