Re: Check if a file exists and if not create it - use sysopen

[Discipulus]

Hello Wroof and welcome,

consider that there are many ways to do it in Perl...
Normally a Perl programmer after years of using open meet also his father sysopen to have more granularity on existing or not file.

>perl -e "use strict; use warnings;use Fcntl; my $fh; sysopen ($fh, 'f
+ilefilefile.log', O_WRONLY|O_APPEND ) or die $!"
No such file or directory at -e line 1.

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>ls filefilefile.log
ls: filefilefile.log: No such file or directory

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>perl -e "use strict; use warnings;use Fcntl; my $fh; sysopen ($fh, 'f
+ilefilefile.log', O_WRONLY|O_EXCL|O_CREAT ) or die
 $!"

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>ls filefilefile.log
filefilefile.log

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------
Here are examples of open and sysopen in action.

To open for reading:

open(FH, "<", $path)                                or die $!;
sysopen(FH, $path, O_RDONLY)                        or die $!;
To open for writing, create a new file if needed, or else truncate an 
+old one:

open(FH, ">", $path)                                or die $!;
sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT)        or die $!;
sysopen(FH, $path, O_WRONLY|O_TRUNC|O_CREAT, 0600)  or die $!;
To open for writing, create a new file, but that file must not previou
+sly exist:

sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT)         or die $!;
sysopen(FH, $path, O_WRONLY|O_EXCL|O_CREAT, 0600)   or die $!;
To open for appending, creating it if necessary:

open(FH, ">>", $path)                               or die $!;
sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT)       or die $!;
sysopen(FH, $path, O_WRONLY|O_APPEND|O_CREAT, 0600) or die $!;
To open for appending, where the file must exist:

sysopen(FH, $path, O_WRONLY|O_APPEND)               or die $!;
To open for update, where the file must exist:

open(FH, "+<", $path)                               or die $!;
sysopen(FH, $path, O_RDWR)                          or die $!;
To open for update, but create a new file if necessary:

sysopen(FH, $path, O_RDWR|O_CREAT)                  or die $!;
sysopen(FH, $path, O_RDWR|O_CREAT, 0600)            or die $!;
To open for update, where the file must not exist:

sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT)           or die $!;
sysopen(FH, $path, O_RDWR|O_EXCL|O_CREAT, 0600)     or die $!;
We use a creation mask of 0600 here only to show how to create a priva
+te file. The argument is normally omitted.

HtH
L*

UPDATE: some docs are missing

[t-rex]

i get bare word error when i complie the script using flags O_RDWR or others, what could be the reason ?

[Discipulus]

have you imported the module with use Fcntl ? see Fcntl

L*