Programming Perl

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3.2.116 read


This function attempts to read LENGTH bytes of data into variable SCALAR from the specified FILEHANDLE. The function returns the number of bytes actually read, 0 at end-of-file. It returns the undefined value on error. SCALAR will be grown or shrunk to the length actually read. The OFFSET, if specified, says where in the variable to start putting bytes, so that you can do a read into the middle of a string.

To copy data from filehandle FROM into filehandle TO, you could say:

while (read FROM, $buf, 16384) {
    print TO $buf;

Note that the opposite of read is simply a print, which already knows the length of the string you want to write, and can write a string of any length.

Perl's read function is actually implemented in terms of standard I/O's fread(3) function, so the actual read(2) system call may read more than LENGTH bytes to fill the input buffer, and fread(3) may do more than one system read(2) in order to fill the buffer. To gain greater control, specify the real system call using sysread. Calls to read and sysread should not be intermixed unless you are into heavy wizardry (or pain).

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