How do you compare strings in Perl?

Question

Practicing Perl for the first time today. I want to loop until a user types "quit". Entering "quit" does not stop and it is an infinite loop. Am I using string comparison wrong? I have this originally:

do 
{
    print "Enter a sentence or phrase to convert or 'quit': ";
    $choice = <STDIN>;  # user input variable
} while ($choice ne "quit");

I also tried creating a separate variable to store and check for in the do-while loop but still an infinite loop:

$quit = "quit";

do 
{
    print "Enter a sentence or phrase to convert to or 'quit': ";
    $choice = <STDIN>;  # init user input variable
    $dif = $quit ne $choice;
} while ($dif == 1);

Schwern · Accepted Answer · 2022-07-29 02:12:41Z

3

$choice = <STDIN> reads a line from stdin including the newline at the end.

You either need to check for "quit\n" or remove the newline with chomp.

answered Jul 29, 2022 at 2:12

Schwern

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4 Comments

Manny Over a year ago

THANK YOU, coming from C++, I had no idea perl requires the newline marker to specify. Also thank you for explaining more how <STDIN> works

Schwern Over a year ago

@Manny C++ also requires the newline character, == is exact. However, cin only reads up to the first whitespace character so it does not read the newline. <filehandle> reads the whole line.

Schwern Over a year ago

@Manny Also, don't do this while ($dif == 1). $quit ne $choice might happen to return 1, but it is documented to return true. Instead just check if it's true: while($dif). It's a common mistake to check for 0 or 1 instead of false and true.

ikegami Over a year ago

@Manny, Re "I had no idea perl requires the newline marker to specify.", To specify what, then end of the line? That's the definition of a line. Then end of the string? No, a LF does not indicate the end of a string, nor is it needed at the end of string. You read a line that contained a LF, and you didn't remove it (e.g. by using chomp). It has nothing to do with Perl

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