File Open In Perl Error Handling
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File Handling In Perl With Examples
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up vote 2 down vote favorite I want to do some task when the file is not opened in the Perl program below. But when I run it, I am getting syntax errors. What's wrong with it? my $LOGPATH = $ENV{DATA_OU}; my $LOGFILE = "cdj_rep" . "." . "test" . ".rpt"; if ! (open(OUT,">$LOGPATH/test1/work/$LOGFILE")) { print "testin"; return; } close(OUT); perl mod-perl perl-module share|improve this question perl dbi error handling edited Jul 13 '10 at 1:08 Greg Bacon 75.5k17147197 asked Jul 13 '10 at 0:24 Arav 98194082 add a comment| 2 Answers 2 active oldest votes up vote 8 down vote accepted The ! needs to go inside the brackets: if (! open (out, share|improve this answer answered Jul 13 '10 at 0:30 user181548 Thanks a lot for the info –Arav Jul 13 '10 at 1:26 add a comment| up vote 9 down vote I'd write it as my $LOGPATH = $ENV{DATA_OU}; my $LOGFILE = "cdj_rep.test.rpt"; my $path = "$LOGPATH/test1/work/$LOGFILE"; open my $fh, ">", $path or do { warn "$0: open $path: $!"; return; }; close $fh or warn "$0: close $path: $!"; Place the entire path in $path so you don't have to repeat it multiple times, and if you ever need to change it, you can do so in one place. The call to open uses a lexical filehandle (my $fh) rather than a bareword handle. This is a good habit to develop because passing $fh to subs or stuffing it inside data structures tends to be more natural syntactically. It also uses the 3-argument form of open so you d
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> open Please note: Many features of this site require JavaScript. You appear to have JavaScript disabled, or are running perl open for write a non-JavaScript capable web browser. To get the best experience, please enable JavaScript or download a modern web browser such as Internet Explorer 8, Firefox, Safari, or Google Chrome. Recently read open http://stackoverflow.com/questions/3233327/perl-open-file-error-handling Perl functions A-Z | Perl functions by category | The 'perlfunc' manpage open FILEHANDLE,EXPR open FILEHANDLE,MODE,EXPR open FILEHANDLE,MODE,EXPR,LIST open FILEHANDLE,MODE,REFERENCE open FILEHANDLE Opens the file whose filename is given by EXPR, and associates it with FILEHANDLE. Simple examples to open a file for reading: open(my $fh, "<", "input.txt") or die "Can't open < input.txt: $!";and for writing: open(my $fh, ">", "output.txt") or die "Can't open > http://perldoc.perl.org/functions/open.html output.txt: $!";(The following is a comprehensive reference to open: for a gentler introduction you may consider perlopentut.) If FILEHANDLE is an undefined scalar variable (or array or hash element), a new filehandle is autovivified, meaning that the variable is assigned a reference to a newly allocated anonymous filehandle. Otherwise if FILEHANDLE is an expression, its value is the real filehandle. (This is considered a symbolic reference, so use strict "refs" should not be in effect.) If three (or more) arguments are specified, the open mode (including optional encoding) in the second argument are distinct from the filename in the third. If MODE is < or nothing, the file is opened for input. If MODE is >, the file is opened for output, with existing files first being truncated ("clobbered") and nonexisting files newly created. If MODE is >> , the file is opened for appending, again being created if necessary. You can put a + in front of the > or < to indicate that you want both read and write access to the file; thus +< is almost always preferred for read/write updates--the +> mode would clobber the
(use strict; use warnings;) Debugging Perl scripts Comments Documentation of Perl POD - Plain Old Documentation Perl on the command line (screencast) Exercise: Hello World Solution: Hello World part 1 Solution: http://perlmaven.com/beginner-perl-maven-open-file-with-error-handling Hello World part 2 (what is the difference between comment and POD?) Scalars http://www.tutorialspoint.com/perl/perl_error_handeling.htm Scalar values and variables Common Errors and Warnings Variable interpolation - User Input and Output - chomp Numerical Operators String operators The 'if' statement Comparison Operators String to number conversion Compare Values undef Logical Operators in Perl True False Short Circuit String functions: index Substr strings in double quotes strings in single error handling quotes Scope of Variables rand() and int() Here documents Exercise: rectangular Solution: area of rectangular Solution: area prompt and warn Solution: concatenation Exercise: number guessing game Solution: number guessing game Files die, warn, exit Open file Open file all Open file with error handling Open or die No such file read one line while loop Read file line by line Write to file Sum numbers perl error handling in a file Debug sum numbers Analyze Apache log file Old style open Exercise: add more statistics Solution: add more statistics Exercise: write report to file Solution: write report to file Lists and Arrays Lists in Perl List assignment foreach loop over list Creating an array Array assignment Exercise: more statistics Array indexes Array indexes (screencast) Looks like number Command line parameters Command line parameters (screencast) Process command line using Getopt::Long Process command line using Getopt::Long (screencast) Process CSV file Process CSV file short version One-liner sum of column in CSV Process CSV file using Text::CSV_XS Join Exercise: improve the color selector Solution: improve the color selector Solution: improve the color selector - check input Solution: improve the color selector - force Solution: improve the color selector - colors.txt Solution: improve the color selector - filename Exercise: improve number guessing game Solution: number guessing game - multiple guesses Solution: number guessing game - exit Solution: number guessing game - s show Solution: number guessing game - n next game Solution: number guessing game - d debug toggle Solution: number guessing game - m move toggle Advanced Arrays The year of 19100 array in
Perl IF..ELSE.. Perl Loopings Perl Operators Perl Files & I/O Regular Expressions Perl Subroutines Perl Formats Perl Error Handling Perl Coding Standard Advanced PERL Perl Sockets Writing Perl Modules Object Oriented Perl Database Management CGI Programming PERL References Perl Functions Selected Reading Computer Glossary Who is Who Copyright © 2014 by tutorialspoint Home References About TP Advertising Error Handling in PERL Advertisements You can identify and trap an error in a number of different ways. Its very easy to trap errors in Perl and then handling them properly. Here are few methods which can be used. Using if The if statement is the obvious choice when you need to check the return value from a statement; for example: if (open(DATA,$file)) { ... } else { die "Error: Couldn't open the file $!"; } Here variable $! returns the actual error message Alternatively, we can reduce the statement to one line in situations where it makes sense to do so; for example: die "Error: Something went wrong\n" if (error()); Using unless The unless function is the logical opposite to if: statements can completely bypass the success status and only be executed if the expression returns false. For example: unless(chdir("/etc")) { die "Error: Can't change directory!: $!"; } The unless statement is best used when you want to raise an error or alternative only if the expression fails. The statement also makes sense when used in a single-line statement: die "Error: Can't change directory!: $!" unless(chdir("/etc")); Here we die only if the chdir operation fails, and it reads nicely. Using the Conditional Operator For very short tests, you can use the conditional operator: print(exists($hash{value}) ? 'There' : 'Missing',"\n"); It's not quite so clear here what we are trying to achieve, but the effect is the same as using an if or unless statement. The conditional operator is best used when you want to quickly return one of two values within an expression or statement. The Warn Function The warn function just raises a warning, a message is printed to STDERR, but no further action is taken. chdir('/etc') or warn "Can't change directory"; The Die Function The die function works just like warn, except that it also calls exit. Within a normal script, this function has the effect of immediately terminating execution. chdir('/etc') or die "Can't change directory"; Reporting Errors Within Modules The