I did a simple script using perl and I was wondering how I can pause the program or return it to the action before? I have this code
print "put your name:";
$s=<>;
and it didn't output anything. I want the program to repeat the same action, i.e. asking the user to enter his name instead of progressing.
my $s = '';
while ($s eq '') {
print "put your name:";
chomp($s = <>);
}
print "The name you entered is $s \n";
No need to set $name to anything before you start - just define it:
my $name;
while ( not length $name ) { #Thx Dave Cross
print "What is your name? ";
$name = <STDIN>;
chomp $name;
}
In Perl, variables defined with my (and that should be 99% of your variables) have a limited scope. If they're defined in a block (something that uses curly braces like this while loop), they'll lose their value once they leave the block. That's why I have to have my $name; before the while.
The while ( not $name ) { will work if $name isn't defined or is a null value, so this will loop until I enter something into $name that's not null.
The chomp removes the NL character that I enter when I press the <ENTER> key. You should always chomp your variables after a read of any sort. Just get use to it.
In this form, the loop is self documenting. I am looping while $name isn't filled in.
You can combine the chomp with the input like this:
my $name;
while ( not $name ) {
print "What is your name? ";
chomp ( $name = <STDIN> );
}
Some people like this because it's a bit shorter, but I don't know if its any clearer. I'm a fan of code clarity because it's easier to maintain.
sub readstr {
while (my $in = <>) {
chomp $in;
return $in if length $in;
}
"";
}
print "put your name:";
my $s = readstr();
Related
In my below program, I was trying to search a string from no of files In a folder but output Is printing in continuous manner rather than stopping after required search. Can some one pls help to point out the error ?
i.e. I am trying to Search the string "VoLTE SIPTX: [SIPTX-SIP] ==> REGISTER" from #files but I am not getting the desired output but I am getting repetitive output of my strings.
# #!/usr/bin/perl
# use strict;
use warnings;
&IMS_Compare_Message();
sub IMS_Compare_Message
{
print "Entering the value i.e. the IMS Message to compare with";
my $value = '';
my $choice = '';
my $loop = '';
print "\nThe script path & name is $0\n";
print "\nPlease enter desired number to select any of the following
(1) Start Comparing REGISTER message !!
(2) Start Comparing SUBSCRIBE message
(3) Start Comparing INVITE message \n";
$value = <STDIN>;
if ($value == 1 )
{
print "\n Start Comparing REGISTER message\n\n";
$IMS_Message = "VoLTE SIPTX: [SIPTX-SIP] ==> REGISTER";
#chomp ($IMS_Message);
}
elsif ($value == 2)
{
print "\n SUBSCRIBE message Flow\n\n";
}
elsif ($value == 3)
{
print "\n INVITE message Flow\n\n";
}
else
{
print "\nThe input is not valid!\n";
print "\nDo you want to continue selecting a Automation Mode again (Y or N)?\n";
$choice = <STDIN>;
if( $choice =~ /[Yy]/) {
test_loop();
} else {
exit;
}
}
my $kw = "$IMS_Message";
my #files = grep {-f} (<*main_log>);
foreach my $file (#files)
{
open(my $fh, '<', $file) or die $!;
my #content = <$fh>;
close($fh);
my $l = 0;
$search = chomp ($kw);
#my $search = quotemeta($kw);
foreach (#content)
{ # go through every line for this keyword
$l++;
if (/$search/)
{
printf 'Found keyword %s in file %s, line %d:%s'.$/, $kw, $file, $l, $_
}
}
}
}
After Modificaiton
# #!/usr/bin/perl
use strict;
use warnings;
print "Entering the value i.e. the IMS Message to compare with";
my $value = '';
my $choice = '';
my $loop = '';
my $IMS_Message = '';
my $search = '';
my $kw = '';
print "\nThe script path & name is $0\n";
print "\nPlease enter desired number to select any of the following
(1) Start Comparing REGISTER message !!
(2) Start Comparing SUBSCRIBE message
(3) Start Comparing INVITE message \n";
$value = <STDIN>;
if ($value == 1 )
{
print "\n Start Comparing REGISTER message\n\n";
$IMS_Message = "VoLTE SIPTX: [SIPTX-SIP] ==> REGISTER";
#chomp ($IMS_Message);
}
elsif ($value == 2)
{
print "\n SUBSCRIBE message Flow\n\n";
}
elsif ($value == 3)
{
print "\n INVITE message Flow\n\n";
}
else
{
print "\nThe input is not valid!\n";
print "\nDo you want to continue selecting a Automation Mode again (Y or N)?\n";
$choice = <STDIN>;
if( $choice eq /[Yy]/) {
test_loop();
} else {
exit;
}
$kw = $IMS_Message;
$search = qr/\Q$kw/;
for my $file ( grep { -f } glob '*main_log' ) {
open my $fh, '<', $file or die qq{Unable to open "$file" for input: $!};
while ( <$fh> ) {
if ( /$search/ ) {
printf "Found keyword %s in file %s, line %d: %s\n", $kw, $file, $., $_;
last;
}
}
}
}
Here are some observations on your code
Your approach to debugging appears to be to try things at random to see if they work. It would be far more fruitful to add diagnostic print statements so that you can compare variables' actual values with what you expect
Error and warning messages are useful information, and it is foolish to comment out use strict to make them go away
Don't call subroutines with an ampersand &. That hasn't been best practice for twenty years now
Lay your code out tidily and cinsistently, so that both you and any people you ask for help can read it easily. As it stands it is impossible to tell where blocks start and end without counting brace characters {...}
Variables should be declared with my as close as possible to their first point of use, and not all at once at the top of the file or subroutine
chomp is necessary only for strings that have been read from the terminal or from a file. It returns the number of characters removed, not the trimmed string
if( $choice =~ /[Yy]/ ) { ... } will check only whether the string contains a Y, so if the operator enters MARRY ME! it will return true. You should use string equality eq to check whether a single Y character has been typed
You shouldn't put scalar variables alone inside double quotes. At best it will make no difference, and just add noise to your code; at worst it will completely change the value of the variable. Just my $kw = $IMS_Message is correct
Unless you require non-sequential access to the contents of a file, it is best to use a while loop to read and process it line by line, rather than read the whole thing into an array and process each element of the array. This also allows you to use the built-in line number variable $. instead of implementing your own $l
The main problem is that you have derived $search from the result of chomp $kw, which sets $search to the number of characters removed by chomp. This is always zero because $kw is a copy of $IMS_Message, which has no newline at the end. That means you are checking all the lines of every file for the character 0, and not for the message that you intended. The correct way is my $search = quotemeta($kw) which you had in place but have commented out, presumably as a result of your policy of "debugging by guesswork"
Fixing these things, your code should look something like this
my $search = qr/\Q$kw/;
for my $file ( grep { -f } glob '*main_log' ) {
open my $fh, '<', $file or die qq{Unable to open "$file" for input: $!};
while ( <$fh> ) {
if ( /$search/ ) {
printf "Found keyword %s in file %s, line %d: %s\n", $kw, $file, $., $_;
last;
}
}
}
New to Perl. Using Windows 10 w/ Padre IDE. I have a question that has been stumping me and it's probably very simple yet I have yet to find an answer on the net.
Here is the code that is working up until my search. It reads a list.txt file with names and matching phone numbers so I have two hashes (one is name => number, the second is number =>).
my $search = "";
print "File name to be read in: ";
my $textFile = <>;
open FILE, $textFile;
my %hash;
while (<FILE>)
{
chomp;
my ($key, $val) = split / /;
$hash{$key} .= exists $hash{$key} ? "$val" : $val;
}
close FILE;
open FILE, $textFile;
my %hash2;
while (<FILE>)
{
chomp;
my ($val, $key) = split / /;
$hash2{$key} .= exists $hash2{$key} ? "$val" : $val;
}
close FILE;
print "(N) for name (#) for number search and (.) to exit: ";
$search = <>;
if ($search == "N") #heres where we have the problem
{
print "Enter name: ";
my $person = <>; #user defined search looks for Bob Smith
print $hash{$person}; #prints nothing
}
However, when I make the search non-user defined, it works perfected as in:
if ($search == "N")
{
#print "Enter name: ";
#my $person = <>;
print $hash{"Bob Smith"}; #prints Bob Smith's number
}
For the record, I had $search print to screen to verify that there was no issue whenI entered the name in the first place. When I user-define the search, the hash will not pull up. When the name is specically coded into the hash function, it works every time.
Thank you for helping a stumped Perl Noobie.
You have a trailing newline character. You need to chomp before you compare:
$search = <>;
chomp $search;
Also, you should use the string compare eq:
if ($search eq "N")
What does ".=" mean in Perl (dot-equals)? Example code below (in the while clause):
if( my $file = shift #ARGV ) {
$parser->parse( Source => {SystemId => $file} );
} else {
my $input = "";
while( <STDIN> ) { $input .= $_; }
$parser->parse( Source => {String => $input} );
}
exit;
Thanks for any insight.
The period . is the concatenation operator. The equal sign to the right means that this is an assignment operator, like in C.
For example:
$input .= $_;
Does the same as
$input = $input . $_;
However, there's also some perl magic in this, for example this removes the need to initialize a variable to avoid "uninitialized" warnings. Try the difference:
perl -we 'my $x; $x = $x + 1' # Use of uninitialized value in addition ...
perl -we 'my $x; $x += 1' # no warning
This means that the line in your code:
my $input = "";
Is quite redundant. Albeit some people might find it comforting.
For pretty much any binary operator X, $a X= $b is equivalent to $a = $a X $b. The dot . is a string concatenation operator; thus, $a .= $b means "stick $b at the end of $a".
In your code, you start with an empty $input, then repeatedly read a line and append it to $input until there's no lines left. You should end up with the entire file as the contents of $input, one line at a time.
It should be equivalent to the loopless
local $/;
$input = <STDIN>;
(define line separator as a non-defined character, then read until the "end of line" that never comes).
EDIT: Changed according to TLP's comment.
You have found the string concatenation operator.
Let's try it :
my $string = "foo";
$string .= "bar";
print $string;
foobar
This performs concatenation to the $input var. Whatever is coming in via STDIN is being assigned to $input.
I have two arrays, one with search terms and another which is multiple lines fetched from a file. I have a nested foreach statement and am searching for for all combinations, but only the very last match is showing even though I know for a fact that there are many other matches!! I have tried many different versions of the code but here is my last one:
open (MYFILE, 'searchTerms.txt');
open (MYFILE2, 'fileToSearchIn.xml');
#searchTerms = <MYFILE>;
#xml = <MYFILE2>;
close(MYFILE2);
close(MYFILE);
$results = "";
foreach $searchIn (#xml)
{
foreach $searchFor (#searchTerms)
{
#print "searching for $searchFor in: $searchIn\n";
if ($searchIn =~ m/$searchFor/)
{
$temp = "found in $searchIn \n while searching for: $searchFor ";
$results = $results.$temp."\n";
$temp = "";
}
}
}
print $results;
You should always use strict and use warnings at the start of your program, and declare all variables at the point of their first use using my. This applies especially when you are asking for help with your code as this measure can quickly reveal many simple mistakes.
As Raze2dust has said it is important to remember that lines read from a file will have a trailing newline "\n" character. If you were checking for exact matches between a pair of lines then this wouldn't matter, but since it's not working for you I assume the strings in searchTerms.txt can appear anywhere in the lines of fileToSearchIn.xml. That means you need to use chomp the strings from searchTerms.txt; lines from the other file can stay as they are.
Things like this are made a lot easier by using the File::Slurp module. It does all the file handling for you and will chomp any newlines from the input text if you ask.
I have changed your program to use this module so that you can see how it works.
use strict;
use warnings;
use File::Slurp;
my #searchTerms = read_file('searchTerms.txt', chomp => 1);
my #xml = read_file('fileToSearchIn.xml');
my #results;
foreach my $searchIn (#xml) {
foreach my $searchFor (#searchTerms) {
if ($searchIn =~ m/$searchFor/) {
push #results, qq/Found in "$searchIn"\n while searching for "$searchFor"/;
}
}
}
print "$_\n" for #results;
chomp your inputs to remove newline characters:
open (MYFILE, 'searchTerms.txt');
open (MYFILE2, 'fileToSearchIn.xml');
#searchTerms = <MYFILE>;
#xml = <MYFILE2>;
close(MYFILE2);
close(MYFILE);
$results = "";
foreach $searchIn (#xml)
{
chomp($searchIn);
foreach $searchFor (#searchTerms)
{
chomp($searchFor);
#print "searching for $searchFor in: $searchIn\n";
if ($searchIn =~ m/$searchFor/)
{
$temp = "found in $searchIn \n while searching for: $searchFor ";
$results = $results.$temp."\n";
$temp = "";
}
}
}
print $results;
Basically, you are thinking you are searching for 'a', but actually it is searching for 'a\n' because that is how it reads the input unless you use chomp. It matches only if 'a' is the last character because in that case, it will be succeeded by a newline.
I am creating a perl script that takes in the a file (example ./prog file)
I need to parse through the file and search for a string. This is what I thought would work, but it does not seem to work. The file is one work per line containing 50 lines
#array = < >;
print "Enter the word you what to match\n";
chomp($match = <STDIN>);
foreach $line (#array){
if($match eq $line){
print "The word is a match";
exit
}
}
You're chomping your user input, but not the lines from the file.
They can't match; one ends with \n the other does not. Getting rid of your chomp should solve the problem. (Or, adding a chomp($line) to your loop).
$match = <STDIN>;
or
foreach $line (#array){
chomp($line);
if($match eq $line){
print "The word is a match";
exit;
}
}
Edit in the hope that the OP notices his mistake from the comments below:
Changing eq to == doesn't "fix" anything; it breaks it. You need to use eq for string comparison. You need to do one of the above to fix your code.
$a = "foo\n";
$b = "bar";
print "yup\n" if ($a == $b);
Output:
yup