Perl Programming/Regular Expression Operators

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Match a string[edit]

# Shorthand form uses // to quote the regular expression
$Text =~ /search words/;
# The m function allows you to use your choice of quote marks
$Text =~ m|search words|;
$Text =~ m{search words};
$Text =~ m<search words>;
$Text =~ m#search words#;


Split a string into parts[edit]

# The split function allows you to split a string wherever a regular expression is matched
@ArrayOfParts = split( /,/, $Text);     # Splits wherever a comma is found
@ArrayOfParts = split( /\s+/, $Text);   # Splits where whitespace is found
@ArrayOfParts = split( /,\s*/, $Text);  # Comma followed by optional whitespace
@ArrayOfParts = split( /\n/, $Text);    # Newline marks where to split


Search and replace a string[edit]

# The s function allows you to search and replace within a string. s(ubstitute)
$Text =~ s/search for/replace with/;
$Text =~ s|search for|replace with|;
$Text =~ s{search for}{replace with};
# Putting a g (global) at the end, means it replaces all occurances and not just the first
$Text =~ s/search for/replace with/g;
# As with everything, putting an i (insensitive) at the end ignores the differences between
# uppercase and lowercase.
Use Locale;
$Text =~ s/search for/replace with/i;


Extracting values from a string[edit]

# This function sets the variables $1, $2, $3 ... 
#   to the information that it has extracted from a string.

$Text =~ m/before(.*)after/;
# So, if $Text was "beforeHelloafter", $1 is now "Hello"
  
$Text =~ m/bef(.*)bet(.*)aft/;
# This time, if $Text was "befOnebetTwoaft", $1 is now "One" and $2 is "Two"
# It can also be used to extract certain kind of information.
$Text =~ m|([^=]*)=(\d*)|;
  
#If $Text was "id=889", $1 now equals "id" and $2 equals 889.


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