Basic HTML version of Foils prepared March 30 97

Foil 60 FileHandles I -- open close die (Chapter 10 of Llama Book)

From PERL4 Tutorial for CPS616 Computational Science for Information Age Course CPS616 -- February 1995. by Geoffrey C. Fox


1 Files are like statement labels designated by a string without a special initial character. It is recommended that you use all capitals in such labels
2 STDIN STDOUT STDERR (and diamond <> null name) have been introduced and correspond to UNIX stdin, stdout and stderr (and concatenation of argument files if <> operator)
3 Filehandles allow you to address general files and the syntax is similar to UNIX standard I/O (stdio.h) support
  • open(FILEHANDLE,"unixname"); # opens file unixname for reading -- can use <
  • open(FILEHANDLE,">unixname"); # opens file unixname for writing
  • open(FILEHANDLE,">>unixname"); # opens file unixname in append mode
4 close(FILEHANDLE) closes file
5 Errors can be handled with die construct
6 open(FH,'>'.$criticalfile) || die("Print an error message if file can't be opened\n"); # Note how we add '>' (or ',' '>>') to file name stored in Perl variable

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