Appending a string variable to a fixed string in Perl

Question

I have a variable that is entered at a prompt:

my $name = <>;

I want to append a fixed string '_one'to this (in a separate variable).

E.g. if $name = Smith then it becomes 'Smith_one'

I have tried several various ways which do not give me the right results, such as:

my $one = "${name}_one";

^ The _one appears on the next line when I print it out and when I use it, the _one is not included at all.

Also:

my $one = $name."_one";

^ The '_one' appears at the beginning of the string.

And:

my $end = '_one';
my $one = $name.$end;
or 
my $one = "$name$end";

None of these produce the result I want, so I must be missing something related to how the input is formatted from the prompt, perhaps. Ideas appreciated!

amon · Accepted Answer · 2017-03-04 10:49:02Z

34

Your problem is unrelated to string appending: When you read a line (e.g. via <>), then the record input separator is included in that string; this is usually a newline \n. To remove the newline, chomp the variable:

    my $name = <STDIN>; # better use explicit filehandle unless you know what you are doing
    # now $name eq "Smith\n"
    chomp $name;
    # now $name eq "Smith"

To interpolate a variable into a string, you usually don't need the ${name} syntax you used. These lines will all append _one to your string and create a new string:

    "${name}_one"  # what you used
    "$name\_one"   # _ must be escaped, else the variable $name_one would be interpolated
    $name . "_one"
    sprintf "%s_one", $name
    # etc.

And this will append _one to your string and still store it in $name:

    $name .= "_one"

edited Mar 4, 2017 at 10:49

answered Sep 17, 2012 at 12:49

amon

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3 Comments

dgBP Over a year ago

ahhh that is interesting about the newline character - chomp immediately solves the problem! I'd tried those methods of appending, too, with no luck - but now they all work! Thanks!

Jonathan Leffler Over a year ago

Funny; I was thinking how much better to use "${name}_one" than awkward constructs like "$name\_one" or $name . "_one".

amon Over a year ago

@JonathanLeffler Thank you for your edit. By now, I'm also in the “${foo} is clear syntax, not an anachronistic bash-ism” camp, and that my original suggestions were worse. I've edited accordingly.

3080 · Accepted Answer · 2023-09-18 21:28:09Z

Thanks - that's really helpful. In case it helps anyone else trying to fix / set the date modified of files downloaded from Google Photos or via WhatsApp (which strips all the exif data), I used the following:

This will work with WhatsApp type stuff in the format 'IMG-20170721-WA0009.jpg', and set hours, mins and seconds to 01 01 01

find . -name \* | perl -lne 'my $a=$_; s/[^\d]+(\d{4})(\d{2})(\d{2})-.*/$1$2$3/ && print "touch -t ${_}0101.01\ \"${a}\"" '

this fixes images like '20170721_063856.jpg'

find . -name \* | perl -lne 'my $a=$_; s/.*(\d{4})(\d{2})(\d{2})_(\d{2})(\d{2})(\d{2}).*/$1$2$3$4$5.$6/ && print "touch -t $_\ \"$a\"" '

and again just add the | bash -x to get it to actually execute. Those search an entire directory, in case you're looking for videos / non-jpgs too

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