$string = "123 456 abc";
$string ~= s/ /-/g;
Try that
jdtoronto | [reply]
[d/l] |
Better is $string =~ tr/ /-/; Don't use substitution when transliteration is applicable.
------
We are the carpenters and bricklayers of the Information Age. The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6 Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.
| [reply]
[d/l] |
Better is $string =~ tr/ /-/; Don't use substitution when transliteration is applicable.
Why? I often hear this advice and it usually stems from the fiction that "tr/// is always faster than s///".
A better rule, IMHO, is to use the tool that fits best. In this case, both fit equally well. I personally prefer s/ /-/g because it will be recognized more widely.
If I felt that the requirement was likely to become something like "change ' ' to '-' and tab to '_'", then I might start with tr/ /-/ in expectation of changing it to something like tr/ \t/-_/ (which could be done with s/// but not so cleanly). While if I felt that the requirement was likely to become something like "change whitespace to '-'", then I'd start with s/ /-/g in expectation of changing it to something like s/\s+/-/g (which could be done with tr/// but not so cleanly).
In the very rare case where the performance difference between the two matters, which to use depends on your input. Benchmarking with one 10kB string I get:
Rate 1tr 0tr 0s 1s
1tr 35435/s -- -1% -27% -30%
0tr 35863/s 1% -- -26% -29%
0s 48562/s 37% 35% -- -4%
1s 50833/s 43% 42% 5% --
[ Note that "0s" and "1s" are identical as are "0tr" and "1tr". I usually include such so that runs of each case are interleaved so I get an idea how much variability there is between runs vs. real differences in performance. ]
With a different 10kB string I get:
Rate 0s 1s 0tr 1tr
0s 20623/s -- -2% -38% -38%
1s 20993/s 2% -- -37% -37%
0tr 33175/s 61% 58% -- -1%
1tr 33522/s 63% 60% 1% --
Note that in both cases, the speed difference between s/// vs. tr/// is only a few micro seconds on a 10kB string so this is extremely unlikely to matter either way for the vast majority of uses.
- tye | [reply]
[d/l]
[select] |
Remember, I'm new. Be gentle. I'm simply trying to create a log file that will have the current date and timestamp as the filename. But I can't figure out what is wrong with my code. The only thing I can think of is that the filename I'm trying to use is to long.
#!/usr/local/bin/perl -w
use strict;
my $localtime = scalar localtime;
my $tmp = ".txt";
my $logfile = $localtime.$tmp;
$logfile =~ tr/ /-/;
open( OUTFILE, ">$logfile" );
print OUTFILE "Hello";
close(OUTFILE);
And this is the error I get when trying to run:
print() on closed filehandle OUTFILE at log.pl line 12.
Any hints? | [reply]
[d/l] |
I'm pretty new to perl too, so I don't understand everything about this command line example, but it seems like an easy way to solve your replacement task.
perl -pi.bak 's/ /-/' file.out
-ted- | [reply]
[d/l] |
I like the s/ /-/, but some of the surrounding syntax needs work. I'll present my version(s) first, then explain things.
perl -pe 's/ /-/;' file.in > file.out
or
perl -pi.bak -e 's/ /-/;' file.out
-
All one-liners need the -e flag - that's what tells Perl that you are including the program on the command line. The -e needs to be right next to the code, with a space being optional. See perlrun if my silly explanation isn't sufficient.
-
I included the semi-colon as a good habit. Some one-liners can have more than one command in them, and the semi-colon can only be omitted from the last command. So I always include it.
-
In my first version I replaced the -i.bak with shell redirection. I just don't like in-place editing, no matter how backups are done. (If you erase the data in your file while inplace editing, and you just re-execute the oneliner, you are "editing" an empty file and overwriting your file.bak with emptiness. Result: you clobber all of your data, I hope your backups are quite recent.)
I think that's it. You might want to check out -l for making all the line endings work nicely. This came up on the SPUG mailing list recently (SPUG: Docs on "-l" wrong?), where I described -l as "Automagically takes care of line endings, so you don't have to think about chomp or \n - high DWIMage factor." That's how it was first explained to me, and it covers the basics.
We had one-liners come up on the SPUG mailing list in April (SPUG:Best One-Liners and Scripts for UNIX) and the discussion was quite instructive - that's where I started learning about the flags.
Oh, yeah. One more flag which you need to know: -c will check your code to see if it compiles. Not strictly one-linerish, but it is technically a command line flag. :)
Perl programming and scheduling in the corporate world,
as explained by dragonchild:
"Uhh ... that'll take me three weeks, broken down as follows: 1 day for coding, the rest for meetings to explain why I only need 1 day for coding."
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[d/l]
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