Classic usage of Perl: Use Sysopen() for more control

In order to better control how files are opened, you can use the sysopen() function:

useFcntl;

sysopen(FH,$filename,O_RDWR|O_CREAT,0666)

ordie"Can'topen$filenameforreading/writing/creating :$!";

The function sysopen() takes four parameters. The first parameter is the file handle parameter similar to the open() function. The second parameter is the file name without mode information. The third parameter is The mode parameter is composed of constants combined with the logical OR operation provided by the Fcntl module. The fourth parameter (optional) is an octal attribute value (0666 represents the data file, 0777 represents the program). sysopen() returns true if the file can be opened, false if the file fails to be opened.

Different from the open() function, sysopen() does not provide an abbreviation for mode description, but combines some constants. Moreover, each mode constant has a unique meaning, and they can only be combined through logical OR operations. You can set up a combination of multiple behaviors.

O_RDONLYRead-only

O_WRONLYWrite-only

O_RDWRReadingandwriting

O_APPENDWritesgototheendofthefile

O_TRUNCTruncatethefileifitexisted

O_CREATCreatethefileifitdidn'texist

O_EXCLErrorifthefilealreadyexisted(usedwithO_CREAT)

Use the sysopen() function when you need to be careful, for example, if You plan to add content to the file. If the file does not exist, without creating a new file, you can write like this:

sysopen(LOG,"/var/log/myPRog.log",O_APPEND,0666)

ordie"Can' topen/var/log/myprog.logforappending:$!";

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