FileDirectory manipulation

1
File/Directory manipulation
2
Opening a File

• To read from a file, must use a file handle.
• by convention, all caps
• open a file (for reading)
• open FILE, myfile.txt
• open file if exists, else return false
• open file for writing
• open OUTFILE, gtoutput.txt
• clobber file if exists, else create new
• open file for appending
• open APPFILE, gtgtappend.txt
• open file, positioned at end if exists, else
  create new

3
Reading from a file

• open FILE, myfile.txt
• one_line ltFILEgt
• _at_all_lines ltFILEgt
• _at_all_lines get all remaining lines from
  myfile.txt
• puts each line of file into one member of array
• remember chomp!
• Rewind a file by seeking to the beginning
• seek (FILE, 0, 0)
• see Camel for explanation

4
printing to a file

• open OUTFILE, gtoutput.txt
• print OUTFILE Hello World!\n
• this can be tedious if all outputs are to same
  output file.
• select OUTFILE
• make OUTFILE the default file handle for all
  print statements.

5
Reading a File at Once

• If you have the need to read the entire contents
  of a file into one large scalar,
• There Is More Than One Way To Do It
• Read the file into an array, and join the
  elements
• _at_lines ltFILEgt
• oneline join (, _at_lines)
• Or, set the pre-defined variable / to undefined.
  This variable controls Perls notion of what a
  line is.
• By default, / is equal to \n, meaning that a
  line is terminated by a newline character. If
  / is undefined, a line is terminated by the
  end-of-file marker
• undef /
• oneline ltFILEgt
• This method is known as slurping a file.

6
Close your files!

• open FILE, myfile.txt
• _at_all_lines ltFILEgt
• close FILE
• opening another file to the same filehandle will
  implicitly close the first one.
• dont rely on this. Its not Good Programming
  Practice.

7
File Test Operators

• Test to see if something is true about a file
• full list on page 98 of Camel
• exists, readable, zero size, directory, link,
  text file, etc
• if (-e myfile.txt)
• print file exists, now opening\n
• open FILE, myfile.txt
• can operate on filename or already existing
  filehandle

8
Directory manipulation

• directories can be opened, read, created,
  deleted, much like files.
• take care when doing these operations youre
  affecting your directory structure
• many of the functions success will depend on
  what permissions you have on the specified
  directories.

9
open, read, close

• opendir DIR, public_html
• nextfile readdir DIR
• _at_remaining_files readdir DIR
• closedir DIR

10
Rewind

• opendir DIR, .
• firstfile readdir DIR
• secondfile readdir DIR
• rewinddir DIR
• _at_allfiles readdir DIR

11
Change, Create, and Delete

• chdir ? change working directory.
• mkdir ? create directory (like unix call)
• rmdir ? remove directory (like unix call)
• works if and only if directory is empty
• chdir public_html
• mkdir images
• rmdir temp

12
Dont do useless work

• Theres no reason to change to a directory to
  open a file in that directory
• You can specify the path of the file in the file
  open statement
• open FILE, public_html/index.html
• This opens the file, without going through the
  bother of changing your working directory twice.