Questions tagged [perl]
Perl is a procedural, high-level, general-purpose, dynamic programming language, known for its native support of regular expressions and string parsing capabilities. Please use this tag for questions about Perl in general. For things related to the new (but related) language Raku (formerly "Perl 6"), please use the raku tag. For Perl-style regular expressions in other languages, use the regex tag, or, if they are based on the PCRE library, the pcre tag.
68,101
questions
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votes
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answers
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How to fix a locale setting warning from Perl
When I run perl, I get the warning:
perl: warning: Setting locale failed.
perl: warning: Please check that your locale settings:
LANGUAGE = (unset),
LC_ALL = (unset),
LANG = "en_US.UTF-8"
...
- 13.4k
594
votes
7
answers
113k
views
Why does modern Perl avoid UTF-8 by default?
I wonder why most modern solutions built using Perl don't enable UTF-8 by default.
I understand there are many legacy problems for core Perl scripts, where it may break things. But, from my point of ...
- 8,296
526
votes
6
answers
28k
views
Why is this program valid? I was trying to create a syntax error
I'm running ActiveState's 32 bit ActivePerl 5.14.2 on Windows 7. I wanted to mess around with a Git pre-commit hook to detect programs being checked in with syntax errors. (Somehow I just managed to ...
- 8,986
410
votes
8
answers
224k
views
Match whitespace but not newlines
I sometimes want to match whitespace but not newline.
So far I've been resorting to [ \t]. Is there a less awkward way?
- 38k
353
votes
12
answers
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Why are scripting languages (e.g. Perl, Python, and Ruby) not suitable as shell languages? [closed]
What are the differences between shell languages like Bash (bash), Z shell (zsh), Fish (fish) and the scripting languages above that makes them more suitable for the shell?
When using the command line,...
- 24.3k
347
votes
8
answers
420k
views
Regex to match any character including new lines
Is there a regex to match "all characters including newlines"?
For example, in the regex below, there is no output from $2 because (.+?) doesn't include new lines when matching.
$string = "START ...
- 4,547
326
votes
5
answers
617k
views
How do I break out of a loop in Perl?
I'm trying to use a break statement in a for loop, but since I'm also using strict subs in my Perl code, I'm getting an error saying:
Bareword "break" not allowed while
"strict subs" in use at ./...
- 24.1k
315
votes
24
answers
158k
views
How can I start an interactive console for Perl?
How can I start an interactive console for Perl, similar to the irb command for Ruby or python for Python?
- 45.4k
290
votes
5
answers
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views
What are the differences between Perl, Python, AWK and sed? [closed]
What are the main differences among them? And in which typical scenarios is it better to use each language?
- 3,307
284
votes
13
answers
524k
views
How can I check if a Perl array contains a particular value?
I am trying to figure out a way of checking for the existence of a value in an array without iterating through the array.
I am reading a file for a parameter. I have a long list of parameters I do ...
- 3,915
281
votes
12
answers
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views
Find size of an array in Perl
I seem to have come across several different ways to find the size of an array. What is the difference between these three methods?
my @arr = (2);
print scalar @arr; # First way to print array size
...
- 2,865
268
votes
6
answers
251k
views
What's the difference between Perl's backticks, system, and exec?
Can someone please help me? In Perl, what is the difference between:
exec "command";
and
system("command");
and
print `command`;
Are there other ways to run shell commands too?
- 66.6k
255
votes
34
answers
221k
views
How can I quickly sum all numbers in a file?
I have a file which contains several thousand numbers, each on its own line:
34
42
11
6
2
99
...
I'm looking to write a script which will print the sum of all numbers in the file. I've got a solution,...
- 3,269
244
votes
10
answers
273k
views
How do I use boolean variables in Perl?
I have tried:
$var = false;
$var = FALSE;
$var = False;
None of these work. I get the error message
Bareword "false" not allowed while "strict subs" is in use.
- 4,742
242
votes
24
answers
376k
views
What's the easiest way to install a missing Perl module?
I get this error:
Can't locate Foo.pm in @INC
Is there an easier way to install it than downloading, untarring, making, etc?
217
votes
3
answers
162k
views
How is Perl's @INC constructed?
What are all the ways of affecting where Perl modules are searched for?
or, How is Perl's @INC constructed?
As we know, Perl uses @INC array containing directory names to determine where to search for ...
- 128k
212
votes
8
answers
248k
views
How do I perform a Perl substitution on a string while keeping the original?
In Perl, what is a good way to perform a replacement on a string using a regular expression and store the value in a different variable, without changing the original?
I usually just copy the string ...
- 16.9k
211
votes
7
answers
482k
views
How do I compare two strings in Perl?
How do I compare two strings in Perl?
I am learning Perl, I had this basic question looked it up here on StackOverflow and found no good answer so I thought I would ask.
- 3,519
205
votes
12
answers
131k
views
What is the difference between 'my' and 'our' in Perl?
I know what my is in Perl. It defines a variable that exists only in the scope of the block in which it is defined. What does our do?
How does our differ from my?
- 125k
196
votes
14
answers
387k
views
How do you round a floating point number in Perl?
How can I round a decimal number (floating point) to the nearest integer?
e.g.
1.2 = 1
1.7 = 2
- 2,776
189
votes
11
answers
395k
views
How can I print the contents of a hash in Perl?
I keep printing my hash as # of buckets / # allocated.
How do I print the contents of my hash?
Without using a while loop would be most preferable (for example, a one-liner would be best).
- 2,595
186
votes
23
answers
208k
views
How do I get the full path to a Perl script that is executing?
I have Perl script and need to determine the full path and filename of the script during execution. I discovered that depending on how you call the script $0 varies and sometimes contains the fullpath+...
- 2,550
181
votes
23
answers
117k
views
How can I delete a newline if it is the last character in a file?
I have some files that I'd like to delete the last newline if it is the last character in a file. od -c shows me that the command I run does write the file with a trailing new line:
0013600 n t ...
- 2,268
175
votes
11
answers
243k
views
How do I remove duplicate items from an array in Perl?
I have an array in Perl:
my @my_array = ("one","two","three","two","three");
How do I remove the duplicates from the array?
- 14.1k
172
votes
20
answers
66k
views
while (1) Vs. for (;;) Is there a speed difference?
Long version...
A co-worker asserted today after seeing my use of while (1) in a Perl script that for (;;) is faster. I argued that they should be the same hoping that the interpreter would optimize ...
- 5,931
165
votes
8
answers
123k
views
Best way to give a variable a default value (simulate Perl ||, ||= )
I love doing this sort of thing in Perl: $foo = $bar || $baz to assign $baz to $foo if $bar is empty or undefined. You also have $foo ||= $bletch which will only assign $bletch to $foo if $foo is not ...
- 19.7k
164
votes
6
answers
301k
views
How to match any non white space character except a particular one?
In Perl \S matches any non-whitespace character.
How can I match any non-whitespace character except a backslash \?
- 92.4k
156
votes
9
answers
119k
views
What exactly does Perl's "bless" do?
I understand one uses the "bless" keyword in Perl inside a class's "new" method:
sub new {
my $self = bless { };
return $self;
}
But what exactly is "bless" doing to that hash reference ?...
- 1,795
152
votes
13
answers
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views
grep -P no longer works. How can I rewrite my searches?
It looks like the new version of OS X no longer supports grep -P and as such has made some of my scripts stop working, for example:
var1=`grep -o -P '(?<=<st:italic>).*(?=</italic>)' ...
- 2,561
149
votes
5
answers
130k
views
How do I update all my CPAN modules to their latest versions?
How do I update all my CPAN modules to their latest versions?
- 29.6k
143
votes
78
answers
62k
views
Hidden features of Perl?
What are some really useful but esoteric language features in Perl that you've actually been able to employ to do useful work?
Guidelines:
Try to limit answers to the Perl core and not CPAN
Please ...
142
votes
9
answers
373k
views
How can I pass command-line arguments to a Perl program?
I'm working on a Perl script. How can I pass command line parameters to it?
Example:
script.pl "string1" "string2"
- 6,139
139
votes
6
answers
269k
views
Escaping a forward slash in a regular expression
My question is a simple one, and it is about regular expression escaping. Do you have to escape a forward slash / in a regular expression? And how would you go about doing it?
- 2,611
135
votes
6
answers
140k
views
How can I output UTF-8 from Perl?
I am trying to write a Perl script using the utf8 pragma, and I'm getting unexpected results. I'm using Mac OS X 10.5 (Leopard), and I'm editing with TextMate. All of my settings for both my editor ...
Peter Conrey
135
votes
2
answers
331k
views
How do I enter a multi-line comment in Perl? [duplicate]
Possible Duplicate:
What are the common workarounds for multi-line comments in Perl?
How do I add a multi-line comment to Perl source code?
134
votes
3
answers
393k
views
Check whether a string contains a substring
How can I check whether a given string contains a certain substring, using Perl?
More specifically, I want to see whether s1.domain.example is present in the given string variable.
- 19.6k
133
votes
10
answers
256k
views
How to match a substring in a string, ignoring case
I'm looking for ignore case string comparison in Python.
I tried with:
if line.find('mandy') >= 0:
but no success for ignore case. I need to find a set of words in a given text file. I am ...
- 12.6k
133
votes
4
answers
83k
views
Perl flags -pe, -pi, -p, -w, -d, -i, -t?
I have seen lots of ways of running Perl code or scripts, with different flags. However, when I try to google for what each flag means, I mainly get results to generic Perl sites and no specific ...
- 26.6k
131
votes
18
answers
198k
views
In Perl, how can I read an entire file into a string?
I'm trying to open an .html file as one big long string. This is what I've got:
open(FILE, 'index.html') or die "Can't read file 'filename' [$!]\n";
$document = <FILE>;
close (FILE);
...
125
votes
8
answers
314k
views
How can I check if a file exists in Perl?
I have a relative path
$base_path = "input/myMock.TGZ";
myMock.TGZ is the file name located in input folder.
The filename can change. But the path is always stored in $base_path.
I need to ...
- 1,832
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votes
10
answers
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views
How do I tell CPAN to install all dependencies?
How do I tell CPAN to install all dependencies?
I tried setting these in cpan:
cpan> o conf prerequisites_policy follow
cpan> o conf commit
I still had to answer "y" a couple of times (but ...
- 11.8k
123
votes
9
answers
141k
views
What's the safest way to iterate through the keys of a Perl hash?
If I have a Perl hash with a bunch of (key, value) pairs, what is the preferred method of iterating through all the keys? I have heard that using each may in some way have unintended side effects. ...
- 27.2k
123
votes
4
answers
21k
views
Why are Perl 5's function prototypes bad?
In another Stack Overflow question Leon Timmermans asserted:
I would advice you not to use prototypes. They have their uses, but not for most cases and definitely not in this one.
Why might ...
- 337k
122
votes
7
answers
126k
views
Using output from a previous job in a new one in a GitHub Action
For (mainly) pedagogical reasons, I'm trying to run this workflow in GitHub actions:
name: "We 🎔 Perl"
on:
issues:
types: [opened, edited, milestoned]
jobs:
seasonal_greetings:
runs-on: ...
- 23k
122
votes
10
answers
110k
views
Should I choose ActivePerl or Strawberry Perl for Windows? [duplicate]
I'm totally new to Perl, but I'd like to try it out. I read about two rival distributions available for Windows platform (I guess there's just Perl on other OSes :).
Wikipedia says that Strawberry ...
- 8,482
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votes
8
answers
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views
How to extract string following a pattern with grep, regex or perl [duplicate]
I have a file that looks something like this:
<table name="content_analyzer" primary-key="id">
<type="global" />
</table>
<table name="content_analyzer2" ...
- 2,025
114
votes
7
answers
267k
views
What is the proper way to check if a string is empty in Perl?
I have been using this code to check if a string is empty:
if ($str == "")
{
// ...
}
And also the opposite with the not equals operator...
if ($str != "")
{
// ...
}
This ...
- 38.9k
114
votes
4
answers
73k
views
How are nested capturing groups numbered in regular expressions?
Is there a defined behavior for how regular expressions should handle the capturing behavior of nested parentheses? More specifically, can you reasonably expect that different engines will capture ...
- 165k
111
votes
9
answers
161k
views
How can Perl's print add a newline by default?
In Perl most of my print statements take the form
print "hello." . "\n";
Is there a nice way to avoid keeping all the pesky "\n"s lying around?
I know I could make a new function such as myprint ...
- 59.8k
111
votes
8
answers
70k
views
Why use strict and warnings?
It seems to me that many of the questions in the Perl tag could be solved if people would use:
use strict;
use warnings;
I think some people consider these to be akin to training wheels, or ...
- 67k