How to replace a string in an existing file in Perl

RegexPerl

Regex Problem Overview

I want to replace the word "blue" with "red" in all text files named as 1_classification.dat, 2_classification.dat and so on. I want to edit the same file so I tried the following code, but it does not work. Where am I going wrong?

@files = glob("*_classification.dat");
foreach my $file (@files)
{
    open(IN,$file) or die $!;
    <IN>;
    while(<IN>)
    {
        $_ = '~s/blue/red/g';
        print IN $file;
    }
    close(IN)
}

Regex Solutions

Solution 1 - Regex

Use a one-liner:

$ perl -pi.bak -e 's/blue/red/g' *_classification.dat

Explanation

  • -p processes, then prints <> line by line
  • -i activates in-place editing. Files are backed up using the .bak extension
  • The regex substitution acts on the implicit variable, which are the contents of the file, line-by-line

Solution 2 - Regex

None of the existing answers here have provided a complete example of how to do this from within a script (not a one-liner). Here is what I did:

rename($file, $file . '.bak');
open(IN, '<' . $file . '.bak') or die $!;
open(OUT, '>' . $file) or die $!;
while(<IN>)
{
    $_ =~ s/blue/red/g;
    print OUT $_;
}
close(IN);
close(OUT);

Solution 3 - Regex

> $_='~s/blue/red/g';

Uh, what??

Just

s/blue/red/g;

or, if you insist on using a variable (which is not necessary when using $_, but I just want to show the right syntax):

$_ =~ s/blue/red/g;

Solution 4 - Regex

It can be done using a single line:

perl -pi.back -e 's/oldString/newString/g;' inputFileName

Pay attention that oldString is processed as a Regular Expression.
In case the string contains any of {}[]()^$.|*+? (The special characters for Regular Expression syntax) make sure to escape them unless you want it to be processed as a regular expression.
Escaping it is done by \, so \[.

Categories
Recommended Regex Solutions
Recommended Perl Solutions

Previous Solution:

How to make an inline element appear on new line, or block element not occupy the whole line?

HtmlCss

Next Solution:

Fastest way to do horizontal SSE vector sum (or other reduction)

AssemblyOptimizationFloating PointSseSimd

Attributions

All content for this solution is sourced from the original question on Stackoverflow.

The content on this page is licensed under the Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license.

Content TypeOriginal AuthorOriginal Content on Stackoverflow
Questionuser831579View Question on Stackoverflow
Solution 1 - RegexZaidView Answer on Stackoverflow
Solution 2 - RegexcmbryanView Answer on Stackoverflow
Solution 3 - RegexbartView Answer on Stackoverflow
Solution 4 - RegexRoyiView Answer on Stackoverflow