Perl

1. Perl Day 2

2. Party Time! • What time is it? • Perl has a handy little function called time $Now=time; print("$Now\n"); • Humm…that returns something like: 1252614575 • What the? • That is the number of seconds since January 1st, 1970 at midnight GMT; • Er, that’s not especially helpful…but localtime is: ($sec,$min,$hour,$monthday,$month,$year,$weekday,$yearday,$dst)=localtime(time); • Unfortunately, some of those are not what you’d expect. • Month: Jan is 0. Dec is 11. • The year, tells you how many years its’ been since 1900…so this year it return 109. Thus you usually have to add 1900 to it. • Weekday: 0 is Sunday, 1 is Monday, … 6 is Saturday.

3. WhatTime.pl #!C:\perl\bin\perl.exe ($sec,$min,$hour,$monthday,$month,$year,$weekday,$yearday,$dst)=localtime(time); $year=$year+1900; $month=$month+1; if($hour<10) { $hour=“0”.$hour; } if($min<10) { $min=“0”.$min; } if($sec<10) { $sec=“0”.$sec; } print(“It’s $hour:$min:$sec on $month-$monthday-$year\n”);

4. join • If you have a bunch of stuff in an array, and you want to print them out in a pretty way: @Fruits=(‘apple’,’grape’,’bananna’,’orange’); $Pretty=join(“ **\n”,@Fruits); Print(“$Pretty\n”); apple ** grape ** bananna ** orange **

5. Getting to a particular folder • Perhaps you want perl to look in a folder for a file • First you must tell it to go there chdir(“C:\\temp”); • But what if that directory doesn’t exist? chdir(“C:\\temp”) || die “Unable to change to C:\\temp\n”;

6. Testing Files • Once in a directory you may wish to see if particular files exist, are readable, writable, or executable: $FileName=“test.txt”; if(-r $FileName) { print(“$FileName is readable\n”); } if(-w $FileName) { print(“$FileName is writable\n”); } • There are many available tests, but the most common are: -f (Is this a file) -d (Is this a directory) -r (Is this file readable) -w (Is this file writable) -e (Is this file executable, ie, a script)

7. File Facts • Sometimes knowing a file exists isn’t enough, maybe you want to know how big it is? • stat returns a bunch of info. ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,$atime,$mtime,$ctime,$blksize,$blocks)= stat($filename); • Most of those don’t matter, but some are useful: • 7: $size total size of file, in bytes • 8: $atime last access time in seconds since the epoch • 9: $mtime last modify time in seconds since the epoch

8. Looking inside a file • First you must open the file: open(myfile,”$FileName”) || die “unable to open $FileName\n”; • This creates a “file handle” called “myfile” • Now we can see whats in there, this will read the first line of the file and print it out: $FirstLine=<myfile>; print(“$FirstLine\n”); • The above example gave you 1 line because you assigned it to a scalar, if you assign it to an array you get all lines: @AllLines=<myfile>; $Output=join(“\n”,@AllLines); print(“$Output\n”); • When you are done, you should close the file handle Close(myfile);

9. What if I want to make a file? • To make a file, you open it for writing: open(myfile,”>$FileName”) || die “unable to write to $FileName\n”; • Now you can simply print to the file: print(myfile “Hello World\n”); • Note: If the file exists before you start, it is overwritten (with no warning) • If you wish to leave whats currently in the file and just add more to the bottom of the file, you’d do this: open(myfile,”>>$FileName”) || die “unable to write to $FileName\n”; • Note the 2 >>’s • > means overwrite the file with a new file (lose existing stuff) • >> means append to the file, don’t delete anything. • If the file doesn’t exist >> still creates it.

10. Directories • You may also want to get a list of all files in a directory: opendir(mydir,”$CurrentDir”); @Files=readdir(mydir); closedir(mydir); • Now the Array @Files has a list of all the files in the current directory. • Note, the first 2 elements in this array will always be . and ..: • . Is the current directory • .. Is the current directories parent.