In your sample code int is not doing anything.

Yes and no. It has an effect, but it's not visible since he's not using |, & and/or ^ at the moment.

>perl -le"$_='7'; int if $ARGV[0]; print $_ | '123'" 0
723

>perl -le"$_='7'; int if $ARGV[0]; print $_ | '123'" 1
127
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The effect:

>perl -MDevel::Peek -e"$_='0'; Dump $_; int; Dump $_;"
SV = PV(0x236054) at 0x18447c4
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x1824064 "0"\0
  CUR = 1
  LEN = 4
SV = PVIV(0x238030) at 0x18447c4
  REFCNT = 1
  FLAGS = (IOK,POK,pIOK,pPOK)
  IV = 0
  PV = 0x1824064 "0"\0
  CUR = 1
  LEN = 4
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The better solution:

push @list, 0+$_;
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