I was just reading this article from Gabor Szabo and he pointed out that Devel::Size reports that a simple sub {} is reported as requiring 8,516 bytes of space. Is this reported size correct? If so, why does Perl need to allocate so much space for a single empty subroutine?
$ perl -MDevel::Size=total_size -E'
my $s = "x" x 100_000;
my $x = \$s;
my $y = \$s;
say total_size($x);
say total_size($y);
'
100048
100048
Does that mean that the size of $x and $y combined is 200KB? No. Same idea here.
It's not the size of the sub, but the size of the references, and everything it references, directly and indirectly.
$ perl -MDevel::Size=total_size -E'
sub f { } say total_size(\&f);
${"xxx"}=1; say total_size(\&f);
${"yyy"}=1; say total_size(\&f);
'
5847
5908
5969
As you can see, this is measuring more than just the sub. There appears to be a pointer to the sub's namespace.
Devel::Size doesn't have easily understandable rules for what to include when measuring the size of a a complex item like a subroutine.
Devel::SizeMe is an experimental fork of Devel::Size which uses reference counting to decide what to include, so the result is much more understandable. It also includes ways to visualize the internal structure of the data.
You can find more information of Devel::SizeMe, including links to slides and screencasts, here.
Related
I am trying to create multiple arrays holding random lists of file names referencing the number of elements in another array. How can I append a $cntr var (beginning with cntr=0) to the end of the new array names so they are directly referenced with elements in other array?
Wow I hope that reads somewhat sensible. Here is what I got going on so far that I hope helps make better sense of what I mean:
function fGenRanList() {
cntr=0
while [[ "$cntr" -lt "${#mTypeAr[#]}" ]] ; do
n="${nAr[$cntr]}" ; echo "\$n: $n"
tracks${cntr}=() ; echo "\$tracks${cntr}: $tracks${cntr}"
while ((n > 0)) && IFS= read -rd $'\0' ; do
tracks${cntr}+=("$REPLY")
((n--))
done < <(sort -zuR <(find "${dirAr[$cntr]}" -type f \( -name '*.mp3' -o -name '*.ogg' \) -print0))
((cntr++))
done
}
error I get is:
/home/user/bin/ranSong_multDirs.sh: line 95: syntax error near unexpected token `"$REPLY"'
/home/user/bin/ranSong_multDirs.sh: line 95: ` tracks${cntr}+=("$REPLY")'
But I first commentted out the echo statements from the tracks${cntr}=() array initialization to get rid of a similar error, but unsure whether or not track${cntr} gets initialized in the first place.
By the end I should end up with as many track(n) arrays as there are elements in ${#mTypeAr[#]}, using the numeric var stored in array ${nAr[$cntr]} to determine how many elements each track array will contain.
Maybe I am making things more difficult than need be, trying to implement arrays into older scripts I have both in order to make them a little more efficient, but I guess am driven primarily to get a better handle on using BASH arrays to store vars for similar but multiple processes which I seem to do often in my scripts.
Change this line, which is not valid bash syntax,
tracks${cntr}+=("$REPLY")
to
declare "tracks${cntr}+=($REPLY)"
Rather than having a syntactic assignment, the declare command takes a string that *look*s like an assignment as an argument; that argument is processed by the shell first, so if cntr is currently 3 and $REPLY is foo, the actual assignment performed is
tracks3+=(foo)
The declare command gives you a level of indirection in making parameter assignments.
I have a question about Perl more out of curiosity than necessity. I have seen there are many ways to do a lot of things in Perl, a lot of the time the syntax seems unintuitive to me (I've seen a few one liners doing som impressive stuff).
So.. I know the function split returns an array. My question is, how do I go about printing the first element of this array without saving it into a special variable? Something like $(split(" ",$_))[0] ... but one that works.
You're 99% there
$ perl -de0
Loading DB routines from perl5db.pl version 1.33
Editor support available.
Enter h or `h h' for help, or `man perldebug' for more help.
main::(-e:1): 0
DB<1> $a = "This is a test"
DB<2> $b = (split(" ",$a))[0]
DB<3> p $b
This
DB<4> p "'$b'"
'This'
This should do it:
print ((split(" ", $_))[0]);
You need one set of parentheses to allow you to apply array indexing to the result of a function. The outer parentheses are needed to get around special parsing of print arguments.
Try this out to print the first element of a whitespace separated list. The \s+ regex matches one or more whitespace characters to split on.
echo "1 2 3 4" | perl -pe 'print +(split(/\s+/, $_))[0]'
Also, see this related post.
I'm trying to read in a file as an array of lines and then iterate over it with zsh. The code I've got works most of the time, except if the input file contains certain characters (such as brackets). Here's a snippet of it:
#!/bin/zsh
LIST=$(cat /path/to/some/file.txt)
SIZE=${${(f)LIST}[(I)${${(f)LIST}[-1]}]}
POS=${${(f)LIST}[(I)${${(f)LIST}[-1]}]}
while [[ $POS -le $SIZE ]] ; do
ITEM=${${(f)LIST}[$POS]}
# Do stuff
((POS=POS+1))
done
What would I need to change to make it work properly?
I know it's been a lot of time since the question was answered but I think it's worth posting a simpler answer (which doesn't require the zsh/mapfile external module):
#!/bin/zsh
for line in "${(#f)"$(</path/to/some/file.txt)"}"
{
// do something with each $line
}
#!/bin/zsh
zmodload zsh/mapfile
FNAME=/path/to/some/file.txt
FLINES=( "${(f)mapfile[$FNAME]}" )
LIST="${mapfile[$FNAME]}" # Not required unless stuff uses it
integer POS=1 # Not required unless stuff uses it
integer SIZE=$#FLINES # Number of lines, not required unless stuff uses it
for ITEM in $FLINES
# Do stuff
(( POS++ ))
done
You have some strange things in your code:
Why are you splitting LIST each time instead of making it an array variable? It is just a waste of CPU time.
Why don’t you use for ITEM in ${(f)LIST}?
There is a possibility to directly ask zsh about array length: $#ARRAY. No need in determining the index of the last occurrence of the last element.
POS gets the same value as SIZE in your code. Hence it will iterate only once.
Brackets are problems likely because of 3.: (I) is matching against a pattern. Do read documentation.
Let's say, for the purpose of example, that file.txt contains the following text:
one
two
three
The solution depends on whether or not you'd like to elide the empty lines in file.txt:
Creating an array lines from file file.txt, eliding empty lines:
typeset -a lines=("${(f)"$(<file.txt)"}")
print ${#lines}
Expected output:
3
Creating an array lines from file file.txt, without eliding empty lines:
typeset -a lines=("${(#f)"$(<file.txt)"}")
print ${#lines}
Expected output:
5
In the end, the difference in the resulting array is a result of whether or not the parameter expansion flag (#) is provided during brace expansion.
while read -r line;
do ARRAY+=("$line");
done < file.txt
How can I find the maximum element and its index from an array in shell script. I have an array
a = [-2.2116565098 -2.1238242060 -2.1747941240 -2.3201010162 -2.3677779871 -1.8126464132 -2.1247209755 -2.1190930712 -2.3242384636 -2.1081702064];
Now, I want to find the maximum as well as its index in bash script. Is there a shortcut like in Matlab we have
[C, I] = max(a);
Also, also how can we have multi-dimensional array and get the index and value of minimum and maximum element.
$ x='-2.2116565098 -2.1238242060 -2.1747941240 -2.3201010162 -2.3677779871'
$ IC=(`tr ' ' '\n' <<<$x | cat -n | sort -k2,2nr | head -n1`)
$ I=${IC[0]} C=${IC[1]}
$ echo $I $C
2 -2.1238242060
Shell scripts in general do not support arrays at all, so what you are asking for is impossible. I am not aware of any shells that support multi-dimensional arrays, but some shells do provide minimal support for one dimensional arrays. Some of those shells probably provide convenient ways to perform the operations you need. To find the maximum value and the index in bash, which is one particular shell that does provide primitive support for arrays, you will need to loop over the array (as far as I know). However, bash does not provide good support for floating point values, so before you implement this, you should consider using a different language. Here is an example of one method:
idx=0
maxidx=0
max=${a[0]}
for v in ${a[#]}; do
expr $v \> $max > /dev/null && { maxidx=$idx; max=$v; }
: $((idx++))
done
There may be better techniques within bash for accessing the array, but it is generally a bad idea IMO to use shell specific constructs. If you are going to be using sh, even arrays really ought to be avoided, because not all shells support them. If you want to use a language feature of a non-standard shell, you might as well use perl, python, ruby, or your language of choice.
First I should perhaps explain what I want to do...
I have 'n' amounts of files with 'n' amount of lines. All I know is
that the line count will be even.
The user selects the files that they want. This is saved into an
array called ${selected_sets[#]}.
The program will print to screen a randomly selected 'odd numbered'
line from a randomly selected file.
Once the line has been printed, I don't want it printed again...
Most of it is fine, but I am having trouble creating arrays based on the contents of ${selected_sets[#]}... I think I have got my syntax all wrong :)
for i in ${selected_sets[#]}
do
x=1
linecount=$(cat $desired_path/$i | wc -l) #get line count of every set
while [ $x -le $linecount ]
do ${i}[${#${i}[#]}]=$x
x=$(($x+2)) # only insert odd numbers up to max limit of linecount
done
done
The problem is ${i}[${#${i}[#]}]=$x
I know that I can use array[${#array[#]}]=$x but I don't know how to use a variable name.
Any ideas would be most welcome (I am really stumped)!!!
In general, this type is question is solved with eval. If you want a a variable named "foo" and have a variable bar="foo", you simply do:
eval $bar=5
Bash (or any sh) treats that as if you had typed
foo=5
So you may just need to write:
eval ${i}[\${#${i}[#]}]=$x
with suitable escapes. (A useful technique is to replace 'eval' with 'echo', run the script and examine the output and make sure it looks like what you want to be evaluated.)
You can create named variables using the declare command
declare -a name=${#${i}[#]}
I'm just not sure how you would then reference those variables, I don't have time to investigate that now.
Using an array:
declare -a myArray
for i in ${selected_sets[#]}
do
x=1
linecount=$(cat $desired_path/$i | wc -l) #get line count of every set
while [ $x -le $linecount ]
do
$myArray[${#${i}[#]}]=$x
let x=x+1 #This is a bit simpler!
done
done
Beware! I didn't test any of the above. HTH