Delete characters

[imphasing]

I need to delete the first five characters of a string. Is there an
easy way to do this? It doesn't matter what character, I just need to
delete the first 5. I have a string like this:

45ghsHello There!

or maybe

hf745Hello There!

and I want to get rid of the 45ghs or hf745.

thanks,
Alex

 

[Gunnar Hjalmarsson]

I need to delete the first five characters of a string. Is there an
easy way to do this?

perldoc -f substr

 

[jl_post]

I need to delete the first five characters of a string. Is there an
easy way to do this? It doesn't matter what character, I just need to
delete the first 5. I have a string like this:

45ghsHello There!

or maybe

hf745Hello There!

and I want to get rid of the 45ghs or hf745.

Dear Alex,

Fortunately for you, there is an easy way to do this.

Say you have a string like:

my $string = "45ghsHello There!";

You can remove the first five characters like this:

substr($string, 0, 5, "");

or even like this:

substr($string, 0, 5) = "";


To read more about substr() and what it can do, type:

perldoc -f substr

at any DOS or UNIX prompt.

I hope this helps, Alex.

-- Jean-Luc

 

[John W. Krahn]

I need to delete the first five characters of a string. Is there an
easy way to do this? It doesn't matter what character, I just need to
delete the first 5. I have a string like this:

45ghsHello There!

or maybe

hf745Hello There!

and I want to get rid of the 45ghs or hf745.

my $string = '45ghsHello There!';

$string = substr $string, 5;

Or:

$string = unpack 'x5 a*', $string

Or:

$string =~ s/^.{5}//s;



John

 

[imphasing]

my $string = '45ghsHello There!';

$string = substr $string, 5;

Or:

thanks for all you're help guys! I got it to work.

Alex

 

[imphasing]

now, does anyone know how I would delete all but the LAST 500 lines of
a text file?
I was thinking of a while loop, but my brain fizzled out, and I
couldn't figure out how to do it...any suggestions?

Thanks,
Alex

 

[Eric Schwartz]

now, does anyone know how I would delete all but the LAST 500 lines of
a text file?

Use a circular buffer. Or File::ReadBackwards, I guess.

-=Eric

 

[jl_post]

now, does anyone know how I would delete all but
the LAST 500 lines of a text file?

Here's a "quick and dirty" way to do it:

# Read the file contents into $text.
$text = $1 if $text =~ m/((.*\n){500})$/;
# Print $text back out to a file.

(This may not be the most efficient way to do what you want, but it
works.)

-- Jean-Luc

 

[Axel]

now, does anyone know how I would delete all but the LAST 500 lines of
a text file?
I was thinking of a while loop, but my brain fizzled out, and I
couldn't figure out how to do it...any suggestions?

Maybe something like:

my $file = "qb";
my @line = split /\s+/, `wc -l $file`;
open INFILE, $file or die "Can't open file";
<INFILE> for (1 .. $line[1] - 500);
while (<INFILE>) {
print; # Or do something else
}

Axel

 

[Anno Siegel]

Here's a "quick and dirty" way to do it:

# Read the file contents into $text.
$text = $1 if $text =~ m/((.*\n){500})$/;
# Print $text back out to a file.

(This may not be the most efficient way to do what you want, but it
works.)

It is more effort to read a file in a scalar variable than to read
the lines into an array. Since the problem is line-oriented, that
would be a better solution:

my @text = <FILE>;
print @text[ -500 .. -1];

Anno

 

[John Bokma]

Maybe something like:

my $file = "qb";
my @line = split /\s+/, `wc -l $file`;

Uhm, you have heard of tail?

man tail

[...]

-n, --lines=N
output the last N lines, instead of the last 10
[...]

 

[Anno Siegel]

Here's a "quick and dirty" way to do it:

# Read the file contents into $text.
$text = $1 if $text =~ m/((.*\n){500})$/;
# Print $text back out to a file.

(This may not be the most efficient way to do what you want, but it
works.)

It is more effort to read a file in a scalar variable than to read
the lines into an array. Since the problem is line-oriented, that
would be a better solution:

my @text = <FILE>;
print @text[ -500 .. -1];

Anno

 

[John W. Krahn]

Maybe something like:

my $file = "qb";
my @line = split /\s+/, `wc -l $file`;

Why split() and the array?

chomp( my $line = `wc -l < $file` );

open INFILE, $file or die "Can't open file";
<INFILE> for (1 .. $line[1] - 500);
while (<INFILE>) {
print; # Or do something else
}

John

 

[John Bokma]

Why split() and the array?

chomp( my $line = `wc -l < $file` );

why chomp, why < ?, why using a scalar?

open INFILE, $file or die "Can't open file";
<INFILE> for (1 .. $line[1] - 500);

<INFILE> for 1 .. `wc -l $file` - 500;

 

[jl_post]

It is more effort to read a file in a scalar
variable than to read the lines into an array.
Since the problem is line-oriented, that
would be a better solution:

my @text = <FILE>;
print @text[ -500 .. -1];

I thought about that solution, but I decided not to mention it
because it would generate warnings if the number of lines were less
than 500 (of course, "use warnings;" would have to be turned on as
well).

Giving this more though, I find that this problem is easily
prevented with the following line:

@text = @text[-500 .. -1] if @text > 500;

This line uses the same "if" logic as my solution, while maintaining
the better efficiency of yours.

-- Jean-Luc

 

[Anno Siegel]

It is more effort to read a file in a scalar
variable than to read the lines into an array.
Since the problem is line-oriented, that
would be a better solution:

my @text = <FILE>;
print @text[ -500 .. -1];

I thought about that solution, but I decided not to mention it
because it would generate warnings if the number of lines were less
than 500 (of course, "use warnings;" would have to be turned on as
well).

Giving this more though, I find that this problem is easily
prevented with the following line:

@text = @text[-500 .. -1] if @text > 500;

This line uses the same "if" logic as my solution, while maintaining
the better efficiency of yours.

That's correct, though I was aiming for clarity more than efficiency.
Your solution keeps @text intact if there are fewer than 500 elements.
That is the behavior one usually wants in that case.

Anno