Problem

You want to read a NUL-terminated string from a file, starting at a particular address.

Solution

Set $/ to an ASCII NUL, and read the string with <>:

$old_rs = $/;                       # save old $/ $/ = "\0";                          # NULL seek(FH, $addr, SEEK_SET)           or die "Seek error: $!\n"; $string = <FH>;                     # read string chomp $string;                      # remove NULL $/ = $old_rs;                       # restore old $/

You can use local to save and restore $/ if you want:

{     local $/ = "\0";     # ... }                           # $/ is automatically restored

Discussion

The example program shown in Example 8.5 , bgets , accepts a filename and one or more byte addresses as arguments. Decimal, octal, or hexadecimal addresses may be specified. For each address, the program reads and prints the NULL- or EOF-terminated string at that position:

#!/usr/bin/perl  # 

bgets - get a string from an address in a binary file use IO::Seekable; ($file, @addrs) = @ARGV             or die "usage: $0 addr ..."; open(FH, $file)                     or die "cannot open $file: $!"; $/ = "\000"; foreach $addr (@addrs) {     $addr = oct $addr if $addr =~ /^0/;     seek(FH, $addr, SEEK_SET)         or die "can't seek to $addr in $file: $!";     printf qq{%#x %#o %d "%s"\n}, $addr, $addr, $addr, scalar <>; }

Here's a simple implementation of the Unix strings program:

#!/usr/bin/perl # 

strings - pull strings out of a binary file $/ = "\0"; while (<>) {     while (/([\040-\176\s]{4,})/g) {         print $1, "\n";     } }

See Also

The seek , getc , and ord functions in perlfunc (1) and in Chapter 3 of Programming Perl ; the discussion of qq// in the "Quote and Quote-Like Operators" section of the perlop (1) manpage, and in the "Pick your own quotes" section of Chapter 2 of Programming Perl