$ perl -MMIME::Base64 -e 'print decode_base64("c3luX2Fja0AxNjMuY29t");'
syn_ack#163.com
$ perl -MMIME::Base64 -e 'print decode_base64("AHN5bl9hY2tAMTYzLmNvbQ");'
syn_ack#163.com
The encode string are different, but the decode results are same, why?
Your second string AHN5bl9hY2tAMTYzLmNvbQ decodes to:
�syn_ack#163.com
The unusual character in first position might not be printed by your terminal software.
Contrary to what you said, they are not the same:
$ perl -MMIME::Base64 -E'
say
decode_base64("c3luX2Fja0AxNjMuY29t") eq
decode_base64("AHN5bl9hY2tAMTYzLmNvbQ") ?1:0'
0
So what are they?
$ perl -MData::Dumper -MMIME::Base64 -e'
$Data::Dumper::Useqq = 1;
print Dumper(decode_base64("c3luX2Fja0AxNjMuY29t"))'
$VAR1 = "syn_ack\#163.com";
$ perl -MData::Dumper -MMIME::Base64 -e'
$Data::Dumper::Useqq = 1;
print Dumper(decode_base64("AHN5bl9hY2tAMTYzLmNvbQ"))'
$VAR1 = "\0syn_ack\#163.com";
Related
I want to count the lines in a file and print a string which depends on the line number. But my while loop misses the first line. I believe the while (<>) construct is necessary to increment the $n variable; anyway, is not this construct pretty standard in perl?
How do I get the while loop to print the first line? Or should I not be using while?
> printf '%s\n%s\n' dog cat
dog
cat
> printf '%s\n%s\n' dog cat | perl -n -e 'use strict; use warnings; print; '
dog
cat
> printf '%s\n%s\n' dog cat | perl -n -e 'use strict; use warnings; while (<>) { print; } '
cat
>
> printf '%s\n%s\n' dog cat | perl -n -e 'use strict; use warnings; my $n=0; while (<>) { $n++; print "$n:"; print; } '
1:cat
The man perlrun shows:
-n causes Perl to assume the following loop around your program, which makes it iterate over filename
arguments somewhat like sed -n or awk:
LINE:
while (<>) {
... # your program goes here
}
Note that the lines are not printed by default. See "-p" to have lines printed. If a file named by an
argument cannot be opened for some reason, Perl warns you about it and moves on to the next file.
Also note that "<>" passes command line arguments to "open" in perlfunc, which doesn't necessarily
interpret them as file names. See perlop for possible security implications.
...
...
"BEGIN" and "END" blocks may be used to capture control before or after the implicit program loop, just as in awk.
So, in fact you running this script
LINE:
while (<>) {
# your progrem start
use strict;
use warnings;
my $n=0;
while (<>) {
$n++;
print "$n:";
print;
}
# end
}
Solution, just remove the -n.
printf '%s\n%s\n' dog cat | perl -e 'use strict; use warnings; my $n=0; while (<>) { $n++; print "$n:"; print; }'
Will print:
1:dog
2:cat
or
printf '%s\n%s\n' dog cat | perl -ne 'print ++$n, ":$_"'
with the same result
or
printf '%s\n%s\n' dog cat | perl -pe '++$n;s/^/$n:/'
but the ikegami's solution
printf "one\ntwo\n" | perl -ne 'print "$.:$_"'
is the BEST
There's a way to figure out what your one-liner is actually doing. The B::Deparse module has a way to show you how perl interpreted your source code. It's actually from the O (capital letter O, not zero) namespace that you can load with -M (ikegami explains this on Perlmonks):
$ perl -MO=Deparse -ne 'while(<>){print}' foo bar
LINE: while (defined($_ = readline ARGV)) {
while (defined($_ = readline ARGV)) {
print $_;
}
-e syntax OK
Heh, googling for the module link shows I wrote about this for The Effective Perler. Same example. I guess I'm not that original.
If you can't change the command line, perhaps because it's in the middle of a big script or something, you can set options in PERL5OPT. Then those options last for just the session. I hate changing the original scripts because it seems that no matter how careful I am, I mess up something (how many times has my brain told me "hey dummy, you know what a git branch is, so you should have used that first"):
$ export PERL5OPT='-MO=Deparse'
I'm trying to print the code points for all possible byte values.
My test file :
$ perl -e ' open($fh,">raw_bytes.dat");while($i++<256){ print $fh chr($i-1) } close($fh)'
$ ls -l raw_bytes.dat
-rw-rw-r--+ 1 uuuuu Domain Users 256 Mar 20 15:41 raw_bytes.dat
$
What should go into the below #---> part so that I print the code points of utf8 $x in hexadecimal?
perl -e ' use utf8; open($fh,"<raw_bytes.dat");binmode($fh);
while($rb=read($fh,$x,1)) { utf8::encode($x);
#--->
} '
I tried %02x using printf, but it didn't work. Also, I want the solution only using core modules.
Use unpack('H*'):
$ perl -e '$x="\x80"; utf8::encode($x); print unpack("H*", $x), "\n"'
c280
For your example file I get
$ perl -e 'open($fh, "<", "raw_bytes.dat"); binmode($fh);
while ($rb=read($fh,$x,1)) { utf8::encode($x);
print unpack("H*", $x), "\n";
}'
00
01
02
03
...
7f
c280
c281
c282
c283
...
c3bd
c3be
c3bf
Variants:
$ perl -e '$x="\x80"; utf8::encode($x);
print uc(unpack("H*", $x)), "\n"'
C280
$ perl -e '$x="\x80"; utf8::encode($x);
($r = uc(unpack("H*", $x))) =~ s/(..)/\\X\1/g;
print "$r\n"'
\XC2\X80
# a little bit pointless example, but assume that $x is a provided Perl scalar....
$ perl -e '$x="\N{U+0080}\N{U+0081}";
printf("U+%04x ", ord($_)) foreach(split(//, $x));
print "\n";'
U+0080 U+0081
Please remember the difference between
a scalar holding a raw string: split(//) returns octets, e.g. \x80
a scalar holding a properly encoded string: split(//) returns characters, e.g. \N{U+0080}
I tried %02x using printf, but it didn't work.
You can use
printf "%vX\n", $x;
According to perldoc sprintf:
vector flag
This flag tells Perl to interpret the supplied string as a vector of
integers, one for each character in the string. Perl applies the
format to each integer in turn, then joins the resulting strings with
a separator (a dot . by default). This can be useful for displaying
ordinal values of characters in arbitrary strings.
php -R '$count++' -E 'print "$count\n";' < somefile
will print the number of lines in 'somefile' (not that I would actually do this).
I'm looking to emulate the -E switch in a perl command.
perl -ne '$count++' -???? 'print "$count\n"' somefile
Is it possible?
TIMTOWTDI
You can use the Eskimo Kiss operator:
perl -nwE '}{ say $.' somefile
This operator is less magical than one thinks, as seen if we deparse the one-liner:
$ perl -MO=Deparse -nwE '}{say $.' somefile
BEGIN { $^W = 1; }
BEGIN {
$^H{'feature_unicode'} = q(1);
$^H{'feature_say'} = q(1);
$^H{'feature_state'} = q(1);
$^H{'feature_switch'} = q(1);
}
LINE: while (defined($_ = <ARGV>)) {
();
}
{
say $.;
}
-e syntax OK
It simply tacks on an extra set of curly braces, making the following code wind up outside the implicit while loop.
Or you can check for end of file.
perl -nwE 'eof and say $.' somefile
With multiple files, you get a cumulative sum printed for each of them.
perl -nwE 'eof and say $.' somefile somefile somefile
10
20
30
You can close the file handle to get a non-cumulative count:
perl -nwE 'if (eof) { say $.; close ARGV }' somefile somefile somefile
10
10
10
You can use an END { ... } block to add code that should be executed after the loop:
perl -ne '$count++; END { print "$count\n"; }' somefile
You can also easily put it in its own -e argument, if you want it more separated:
perl -ne '$count++;' -e 'END { print "$count\n"; }' somefile
See also:
perlmod - BEGIN, UNITCHECK, CHECK, INIT and END at perldoc.perl.org.
This should be what you're looking for:
perl -nle 'END { print $. }' notes.txt
In awk I can write: awk -F: 'BEGIN {OFS = FS} ...'
In Perl, what's the equivalent of FS? I'd like to write
perl -F: -lane 'BEGIN {$, = [what?]} ...'
update with an example:
echo a:b:c:d | awk -F: 'BEGIN {OFS = FS} {$2 = 42; print}'
echo a:b:c:d | perl -F: -ane 'BEGIN {$, = ":"} $F[1] = 42; print #F'
Both output a:42:c:d
I would prefer not to hard-code the : in the Perl BEGIN block, but refer to wherever the -F option saves its argument.
To sum up, what I'm looking for does not exist:
there's no variable that holds the argument for -F, and more importantly
Perl's "FS" is fundamentally a different data type (regular expression) than the "OFS" (string) -- it does not make sense to join a list of strings using a regex.
Note that the same holds true in awk: FS is a string but acts as regex:
echo a:b,c:d | awk -F'[:,]' 'BEGIN {OFS=FS} {$2=42; print}'
outputs "a[:,]42[:,]c[:,]d"
Thanks for the insight and workarounds though.
You can use perl's -s (similar to awk's -v) to pass a "FS" variable, but the split becomes manual:
echo a:b:c:d | perl -sne '
BEGIN {$, = $FS}
#F = split $FS;
$F[1] = 42;
print #F;
' -- -FS=":"
If you know the exact length of input, you could do this:
echo a:b:c:d | perl -F'(:)' -ane '$, = $F[1]; #F = #F[0,2,4,6]; $F[1] = 42; print #F'
If the input is of variable lengths, you'll need something more sophisticated than #f[0,2,4,6].
EDIT: -F seems to simply provide input to an automatic split() call, which takes a complete RE as an expression. You may be able to find something more suitable by reading the perldoc entries for split, perlre, and perlvar.
You can sort of cheat it, because perl is actually using the split function with your -F argument, and you can tell split to preserve what it splits on by including capturing parens in the regex:
$ echo a:b:c:d | perl -F'(:)' -ane 'print join("/", #F);'
a/:/b/:/c/:/d
You can see what perl's doing with some of these "magic" command-line arguments by using -MO=Deparse, like this:
$ perl -MO=Deparse -F'(:)' -ane 'print join("/", #F);'
LINE: while (defined($_ = <ARGV>)) {
our(#F) = split(/(:)/, $_, 0);
print join('/', #F);
}
-e syntax OK
You'd have to change your #F subscripts to double what they'd normally be ($F[2] = 42).
Darnit...
The best I can do is:
echo a:b:c:d | perl -ne '$v=":";#F = split("$v"); $F[1] = 42; print join("$v", #F) . "\n";'
You don't need the -F: this way, and you're only stating the colon once. I was hoping there was someway of setting variables on the command line like you can with Awk's -v switch.
For one liners, Perl is usually not as clean as Awk, but I remember using Awk before I knew of Perl and writing 1000+ line Awk scripts.
Trying things like this made people think Awk was either named after the sound someone made when they tried to decipher such a script, or stood for AWKward.
There is no input record separator in Perl. You're basically emulating awk by using the -a and -F flags. If you really don't want to hard code the value, then why not just use an environmental variable?
$ export SPLIT=":"
$ perl -F$SPLIT -lane 'BEGIN { $, = $ENV{SPLIT}; } ...'
I would like to format(truncate/append with chars) a string to a specified length while printing in Perl.
For example
$string='my_string';
printf("%04s",$string);
should print
my_s
also if
$string='my';
I should get
00my
Is there any way to print last four characters ?
ring
and if string is
$string='my';
it should print
00my
You want to do this format string instead of yours:
printf ("%04.4s", $string);
You need the .4 because this specifies maximum length. (The 4 at the beginning specifies a minimum only)
here are the output of some tests:
$ perl -e "my \$string = \"my_string\";print sprintf(\"%04.4s\", 22);"
0022
$ perl -e "my \$string = \"my_string\";print sprintf(\"%04.4s\", \$string);"
my_s
$ perl -e "my \$string = \"my\";print sprintf(\"%04s\", \$string);"
00my
Here is the output using the wrong format string. As you can see strings are not truncated.
$ perl -e "my \$string = \"my_string\";print sprintf(\"%04s\", 22);"
0022
$ perl -e "my \$string = \"my_string\";print sprintf(\"%04s\", \$string);"
my_string
printf('%04s', substr($_, 0, 4));