No Comments Written by Anders on April 18, 2008 – 12:06 pm

The Perl core defines functions equivalent to the C functions. These functions include:

Functions for scalars or strings

chomp, chop, chr, crypt, hex, index, lc, lcfirst, length, oct, ord, pack, q/STRING/, qq/ STRING/, reverse, rindex, sprintf, substr, tr///, uc, ucfirst, y///

Regular expressions and pattern matching

m//, pos, quotemeta, s///, split, study, qr//

Numeric functions

abs, atan2, cos, exp, hex, int, log, oct, rand, sin, sqrt, srand

Functions for real @ARRAYs

pop, push, shift, splice, unshift

Functions for list data

grep, join, map, qw/STRING/, reverse, sort, unpack

Functions for real %HASHes

delete, each, exists, keys, values

Input and output functions

binmode, close, closedir, dbmclose, dbmopen, die, eof, fileno, flock, format, getc, print, printf, read, readdir, rewinddir, seek, seekdir, select, syscall, sysread, sysseek, syswrite, tell, telldir, truncate, warn, write

Functions for fixed length data or records

pack, read, syscall, sysread, syswrite, unpack, vec

Functions for file handles, files or directories

-X, chdir, chmod, chown, chroot, fcntl, glob, ioctl, link, lstat, mkdir, open, opendir, readlink, rename, rmdir, stat, symlink, umask, unlink, utime

Functions for processes and process groups

alarm, exec, fork, getpgrp, getppid, getpriority, kill, pipe, qx/STRING/, setpgrp, setpriority, sleep, system, times, wait, waitpid

Low-level socket functions

accept, bind, connect, getpeername, getsockname, getsockopt, listen, recv, send, setsockopt, shutdown, socket, socketpair

Fetching user and group info

endgrent, endhostent, endnetent, endpwent, getgrent, getgrgid, getgrnam, getlogin, getpwent, getpwnam, getpwuid, setgrent, setpwent

Fetching network info

endprotoent, endservent, gethostbyaddr, gethostbyname, gethostent, getnetbyaddr, getnetbyname, getnetent, getprotobyname, getprotobynumber, getprotoent, getservbyname, getservbyport, getservent, sethostent, setnetent, setprotoent, setservent

Time-related functions

gmtime, localtime, time, times

That was a shortened list; a few segments were culled from the list in the perlfunc documentation.

Perl’s basic I/O uses ‘filehandles’ – these are really just FILE* references as used in C’s stdio library. As always, you start with STDIN, STDOUT, and STDERR; you can open additional file handles for input and/or output. There is a special convenience mechanism for opening file(s) listed on the command line. The simplest mechanism for output is to use the print function, as has been illustrated in earlier code fragments.

By default, print sends its output to STDOUT. Input is typically handled line-by-line. There is a readline function that is roughly the input line handling function equivalent to the output line handling print, but most Perl code uses the ‘diamond’ < > operator. Usually, the diamond operator includes a filehandle, e.g. <STDIN> (or <INPUTFILE> if you have assigned a value to INPUTFILE in a call to the open() file-opening function). An empty diamond operator, <>, is associated with an input stream obtained by concatenating together the contents of all the files listed on the command line. The diamond operator returns the next line from the referenced file:

$line = <STDIN>;

The entire contents of the input line, including the terminating \n character, are assigned to the scalar variable on the left side of the assignment statement. The line input in response to the prompt is read in the $num = <STDIN> line, resulting in a string value in the scalar $num. On the next line, this is used in a construct that requires a numeric value (the repeat factor in the string repetition expression). The input string is automatically coerced to a numeric value (if the input data were not numeric, the resulting value will be zero).

#!/share/bin/perl
   print “What is your name? “;
   $name = <STDIN>;
   chomp($name);
   print “Hello $name, welcome to Perl\n”;

Input of the name Fred would produce the string ‘Fred\n’. This would disrupt output formatting, so here chomp() is used to remove the trailing \n.