search a specific sub string pattern in a string using perl

Question

I'm a newbie to perl, I went through this Check whether a string contains a substring to how to check a substring is present in a string, Now my scenario is little different

I have a string like

/home/me/Desktop/MyWork/systemfile/directory/systemfile64.elf ,

In the end this might be systemfile32.elf or systemfile16.elf,so In my perl script I need to check whether this string contains a a substring in the format systemfile*.elf. How can I achieve this in perl ?

I'm planing to do like this

if(index($mainstring, _serach_for_pattern_systemfile*.elf_ ) ~= -1) {
    say" Found the string";
}

$string =~ /systemfile.*\.elf/ and you should check out perldoc.perl.org/perlre.html — yoniyes
– yoniyes, Commented Oct 25, 2016 at 8:35
and what if a file exist called 64bitsystemfile.elfde? you will still get a match for systemfile and .elf — user2082599
– user2082599, Commented Oct 25, 2016 at 10:44

simbabque · Accepted Answer · 2016-10-25 08:56:43Z

3

You can use the pattermatching

if ($string =~ /systemfile\d\d\.elf$/){
   # DoSomething
}

\d stands for a digit (0-9)

$ stands for end of string

edited Oct 25, 2016 at 8:56

simbabque

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answered Oct 25, 2016 at 8:35

Jens

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2 Comments

Jens Over a year ago

@HariprasadCR: The index function searches for one string within another, but without the wildcard-like behavior of a full regular-expression pattern match

Jens Over a year ago

@HariprasadCR So for me it sounds like you have to do two separate checks if you want to use index

Orabîg · Accepted Answer · 2016-10-25 09:00:34Z

1

Well

if( $mainstring =~ m'/systemfile(16|32)\.elf$' ) {
   say" Found the string";
}

does the job.

For your informations :

$string =~ m' ... '

is the same than

$string =~ / ... /

which checks the string against the given regular expression. This is one of the most useful features of the Perl language.

More info at http://perldoc.perl.org/perlre.html

(I did use the m'' syntax to improve readability, because of the presence of another '/' character in the regexp. I could also write /\/systemfile\d+\.elf$/

edited Oct 25, 2016 at 9:00

answered Oct 25, 2016 at 8:55

Orabîg

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1 Comment

Dave Cross Over a year ago

I agree with using an explicit m on the match operator so that you can change the delimiter. But I think that the single quote is a terrible choice of alternative. It makes the regex look like a string. I would have probably gone with m[systemfile(16|32)\.elf$].

yoniyes · Accepted Answer · 2016-10-25 10:09:48Z

0

if ($string =~ /systemfile.*\.elf/) {
    # Do something with the string.
}

That should match only the strings you seek (given that every time, a given string is stored in $string). Inside the curly brackets you should write your logic.

The . stands for "any character" and the * stands for "as many times you see the last character". So, .* means "any character as many times you see it". If you know that the string will end in this pattern, then it will be safer to add $ at the end of the pattern to mark that the string should end with this:

$string =~ /systemfile.*\.elf$/

Just don't forget to chomp $string to avoid any line-breaks that might mess with your desired output.

edited Oct 25, 2016 at 10:09

answered Oct 25, 2016 at 10:03

yoniyes

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3 Comments

user2082599 Over a year ago

This will also match *systemfile*.elf* the OP specifically says he wants to match systemfile*.elf hence why I answered if ($string =~ /^systemfile.*.\.elf$/);

user2082599 Over a year ago

and I made the same mistake by assuming he wanted to match the filename only without path. :)

yoniyes Over a year ago

this will match strings with the full path as well

score 0 · Accepted Answer · 2016-10-25 10:39:20Z

0

use strict;
use warnings;

my $string = 'systemfile16.elf';
if ($string =~ /^systemfile.*\.elf$/) {
print "Found string $string";
  } else {
print "String not found";

will match systemfile'anythinghere'.elf if you have a set directory.

if you want to search entire string, including directory then:

my $string = 'c:\\windows\\system\\systemfile16.elf';
if ($string =~ /systemfile.*\.elf$/) {
print "Found string $string";
  } else {
print "String not found";

if you only want to match 2 systemfile then 2 numeric characters .elf then use the other methods mentioned above by other answers. but if you want systemanything.elf then use one of these.

edited Oct 25, 2016 at 10:39

answered Oct 25, 2016 at 9:16

user2082599

4 Comments

Jens Over a year ago

You should escape the last dot, because it is the character dot not the placeholder

user2082599 Over a year ago

@Jens. true, I never tested the code. Will update it, although it will work regardless of it being wrong :) so by not escaping the . it will accept systemfile00.self as a match as well, here we want to match exactly .elf only. Thanks for spotting it

Dada Over a year ago

Actually, "systemfile.." is at the end of the string, so you don't want that ^ at the start (and you example string should rather be '/home/me/Desktop/MyWork/systemfile/directory/systemfile09.elf' for instance). Moreover, .* will match anything including strings like systemfile/not/the/right/one/.elf ... So definitely not what the OP would like.

user2082599 Over a year ago

ok, I missed the part where he wanted the entire string, so we should then drop the ^. However he specifies "substring in the format systemfile*.elf" which means systemfile"anythinghere".elf so could be systemfile16.elf, systemfile32.elf or sytemfile64bit.elf in my view.

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