Difference between revisions of "File I/O in Perl"
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| − | + | == Open a file to READ == | |
To open a file and read only the first line: | To open a file and read only the first line: | ||
| − | $strVariable = | + | $strVariable = <BOBSFILE>; |
# remove CR LF | # remove CR LF | ||
$strVariable = chomp($strVariable = ); | $strVariable = chomp($strVariable = ); | ||
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Read and print all lines as well as number them. | Read and print all lines as well as number them. | ||
| − | open (FILE, | + | open (FILE,"$guestbk") || die "Can't Open $guestbk: $!\n"; |
$lnum = 1; | $lnum = 1; | ||
| − | while( $line = | + | while( $line = <FILE> ){ |
chomp($line); | chomp($line); | ||
| − | print | + | print "$lnum: $line\n"; |
$lnum++; | $lnum++; | ||
} | } | ||
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Read all lines into an array. | Read all lines into an array. | ||
| − | @eachline = | + | @eachline = <FILE>; |
chomp(@eachline); | chomp(@eachline); | ||
| − | print | + | print "@eachline"; |
| − | & | + | |
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== Open a file to WRITE == | == Open a file to WRITE == | ||
Latest revision as of 11:49, 24 November 2010
Use a filehandle to open a file in Perl. The filehandle identifier doesn't have a prefix like other Perl identifiers.
To open a file use a FILEHANDLE (a name you decide, all caps isn't a requirement but suggested for clarity) and a FILENAME
open(BOBSFILE, "information.txt");
The above file will be opened for "read" since no i/o type was specified. There are three ways to open a file. This is specified with a symbol before the filename. If no symbol is specified, "read" is assumed.
- read < (open an existing file for read) ex: open BOBSFILE, "<information.txt";
- write > (create a new file to write) ex: open NEWSTORY, ">story.txt";
- append >> (add more to an existing file) ex: open(LOG, ">>activity.log");
open BOBSFILE, "<information.txt"; open NEWSTORY, ">story.txt"; open(LOG, ">>activity.log");
If you open another file using the same FILEHANDLE, Perl will automatically close the previous file and let you use the FILEHANDLE for the new file.
To manually close a FILEHANDLE:
close FILEHANDLE;
Be prepared to deal with uncooperative files.
open(FILEHANDLE, ">bobsinfo.dat") or die("Error");
Web development example.
open (FILE,"$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";
$lnum++;
}
close FILE;
Read all lines into an array.
@eachline = <FILE>; chomp(@eachline); print "@eachline";
Open a file to WRITE
Writing to a file overwrites what was in the file previously and writes the new information over it.
open (GUEST,">$guestbk") || die "Can't Open $guestbookreal: $!\n";
print GUEST "<H1>New Guestbook Entry</H1>\n";
print GUEST "$FORM{'realname'}</a></b>";
print GUEST "<b>Time: </b>$date<br>\n";
print GUEST "<b>Comments: </b>$txtComments<br>\n";
close (GUEST);
Read from one file and write its contents into another file.
my $infile = 'bobsbills.txt'; my $outfile = 'bobsexpenses.txt'; open IN, "< $infile" or die "Can't open $infile : $!"; open OUT, "> $outfile" or die "Can't open $outfile : $!"; print OUT <IN>; close IN; close OUT;
Other Methods of File Access
Here's a quick way to write to a file without using a filehandle.
print `echo "Write this line" > filename.txt"`;
Read without filehandle
$strLines = `cat filename.txt`;
