Difference between revisions of "File I/O in Perl"

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(New page: Use a filehandle to open a file in Perl. The filehandle identifier doesn't have a prefix like other Perl identifiers. To open a file use a FILEHANDLE (a name you decide, all caps isn't a...)
 
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  open(BOBSFILE, "information.txt");
 
  open(BOBSFILE, "information.txt");
  
The above file will be opened for "read" since no i/o type was specified.  There are three ways to open a file. This is specified with a symbol before the filename.  If no symbol is specified, "read" is assumed.
+
The above file will be opened for "read" since no i/o type was specified.  There are three ways to open a file. This is specified with a symbol before the filename.  If no symbol is specified, "read" is assumed.<big>
# read <            (open an existing file for read)   ex: open BOBSFILE, "<information.txt";
+
# '''read''' <            (''open an existing file for read'')   ex: open BOBSFILE, "<information.txt";
# write >            (create a new file to write)   ex: open NEWSTORY, ">story.txt";
+
# '''write''' >            (''create a new file to write'')   ex: open NEWSTORY, ">story.txt";
# append >>            (add more to an existing file)   ex: open(LOG, ">>activity.log");
+
# '''append''' >>            (''add more to an existing file'')   ex: open(LOG, ">>activity.log");</big>
 +
 
 +
open BOBSFILE, "<information.txt";
 +
open NEWSTORY, ">story.txt";
 +
open(LOG, ">>activity.log");
 +
 
 +
If you open another file using the same FILEHANDLE, Perl will automatically close the previous file and let you use the FILEHANDLE for the new file.
 +
 
 +
To manually close a FILEHANDLE:
 +
 
 +
close FILEHANDLE;
 +
 
 +
Be prepared to deal with uncooperative files.
 +
 
 +
open(FILEHANDLE, ">bobsinfo.dat") or die("Error");
 +
 
 +
Web development example.
 +
 
 +
open (FILE,"$guestbk") || die "Can't Open $guestbk: $!\n";
 +
 
 +
&nbsp;
 +
 
 +
== Open a file to READ ==
 +
 
 +
To open a file and read only the first line:
 +
 
 +
$strVariable = <BOBSFILE>;
 +
# remove CR LF
 +
$strVariable = chomp($strVariable = ); 
 +
 
 +
Read and print all lines as well as number them.
 +
 
 +
open (FILE,"$guestbk") || die "Can't Open $guestbk: $!\n";
 +
$lnum = 1;
 +
while( $line = <FILE> ){
 +
  chomp($line);
 +
  print "$lnum: $line\n";
 +
  $lnum++;
 +
}
 +
close FILE;
 +
 
 +
Read all lines into an array.
 +
 
 +
@eachline = <FILE>;
 +
chomp(@eachline);
 +
print "@eachline";
 +
 
 +
&nbsp;
 +
 
 +
== Open a file to WRITE ==
 +
 
 +
 
 +
 
  
 
&nbsp;
 
&nbsp;

Revision as of 10:47, 12 April 2008

Use a filehandle to open a file in Perl. The filehandle identifier doesn't have a prefix like other Perl identifiers.

To open a file use a FILEHANDLE (a name you decide, all caps isn't a requirement but suggested for clarity) and a FILENAME

open(BOBSFILE, "information.txt");

The above file will be opened for "read" since no i/o type was specified. There are three ways to open a file. This is specified with a symbol before the filename. If no symbol is specified, "read" is assumed.

  1. read <            (open an existing file for read)   ex: open BOBSFILE, "<information.txt";
  2. write >            (create a new file to write)   ex: open NEWSTORY, ">story.txt";
  3. append >>            (add more to an existing file)   ex: open(LOG, ">>activity.log");
open BOBSFILE, "<information.txt";
open NEWSTORY, ">story.txt";
open(LOG, ">>activity.log");

If you open another file using the same FILEHANDLE, Perl will automatically close the previous file and let you use the FILEHANDLE for the new file.

To manually close a FILEHANDLE:

close FILEHANDLE;

Be prepared to deal with uncooperative files.

open(FILEHANDLE, ">bobsinfo.dat") or die("Error");

Web development example.

open (FILE,"$guestbk") || die "Can't Open $guestbk: $!\n";

 

Open a file to READ

To open a file and read only the first line:

$strVariable = <BOBSFILE>;
# remove CR LF
$strVariable = chomp($strVariable = );  

Read and print all lines as well as number them.

open (FILE,"$guestbk") || die "Can't Open $guestbk: $!\n";
$lnum = 1;
while( $line = <FILE> ){
  chomp($line);
  print "$lnum: $line\n";
  $lnum++;
}
close FILE;

Read all lines into an array.

@eachline = <FILE>;
chomp(@eachline);
print "@eachline";

 

Open a file to WRITE