Programming :: Perl's Foreach Loop Can't Use An Array Element As The Control Variable?
Jul 22, 2011
I'm reading "OReilly Learning Perl 5th Edition", and there are such words:Code:You can use an array element like $fred[2] in every place? where you could use any other scalavariable like $fred.At the bottom of the page, it explains the ? like this:Code:The most notable exception is that the control variable of a foreach loop, which you?ll see later in this chapter, must be a simple scalar.Since Perl has the save-and-restore mechanism for the control variable, why an array element can't be used as the control variable
it's been a while since I logged on here! I've been trying my hand at a little perl and have hit a brick wall.I'm using the Imagemagick module to manipulate some images. I can get the following to work without issue:
2. for I in 1 2 3 4 5 6 7 8 9 10; do echo $I; done|
3. for I in $(seq 1 10); do echo $I; done|
4. for ((I=1; I <= 10 ; I++)); do echo $I; done
I have a script which uses the 1st form of for loop. I'm trying to modify it to use a variable instead of a static hard-coded value in the section that controls the looping.of the for loop.
I've tried all different ways of quoting and escaping the variable, and the problem is that the quoting chars and escape char are being translated and passed into the loop along with the value stored in the variable.
For example, to change the start value of 1 to whatever value I want passed in through a variable:
Change:
I have tried: {{$a}..10} and {`$a`..10}, to have the variable evaluated first.
I have tried using the eval() function.
I have tried single and double quotes and the backslash escape character.
Nothing I've tried works. It's probably a syntax error.
For Perl I need to understand a few things. It's unlikely that anyone will be able to give me direct answers but if they could point outI'm trying to hack down an existing script http://eoylpac.org/source/eoy.pl. What I need to be able to do (in a nut shell):1. Open a database2. Read the values for each uniq id and execute a subroutine for each of those values. (The subroutine already exists in the above file 'do_pdf').
I'm trying to read content of file to variable and use this variable in for loop. The problem is, when I have c++ comment style in file - /*. Spaces in line are also interpreted as separated lines.
For example:
Code:
Changing $files to "$files" eliminate these problems but causes that whole content of variable is treated as one string (one execution of loop).
I'm writing a perl script to remove a test database and part of that is of course getting rid of all files. So I wrote this to do the job:
Code:
This always results in an "Could not open /u00/app/oracle/product/10.2.0/rdbms/dbs for reading: No such file or directory" (that directory is the one ending with the $spfile_dir variable) message, although that directory exists and the executing user has writing rights on it.
The same behaviour if I create the directory array like this:
Code:
The problem does not occur when one of the directories is the only element in the array though. Of course I could copy and paste that part of the script for the second directory, but I don't like that workaround.
When I deal with an array in a function I con not access to the content of array in a for loop, but out of a for loop I can access to them! for example
[code]...
In a function when I send as parameter, in a for loop it prints the content of array and out of a for loop it prints the address of arr[i]
I need to know how to assign a result from a select. I am clueless on the sytax. I am trying this in bash. Maybe I am not assigning the array right. It gives me the whole row in the echo instead of just field a. How do I get fieldA = a in the select. Note script was stripped for security on database info but the syntax is same.
Code:
#!/bin/sh results="$(mysql --user ${DB_USER} -p${DB_PWD} ${DB_NAME} -Bse 'select a,b,c,d from tblMytable')" for rows in "${results[@]}" do fieldA=${rows[0]}; echo ${fieldA}; done
Program in CSay I have a char array of 1024 bytes called buf1.But I only want to print the chars in index 0 up to index 30. I know I could do this with a for loop. But is there any other way? What about maybe storing from 31-1024 to another char array say buf2 with strcpy and somehow popping 31+ out of the buf1 char array?
I work in a simulations environment. I'm trying to write a bash script that will read fields from a .csv file into an array, the first field being an identifiyng number and the second field being a corresponding url. There are about 1600 of these number/url combinations in the .csv file that i'm reading from. Once that is done i want it to parse a text file and match the number, when it has a match i want it to enter the corresponding url into a particular line in the text file. The script I have written (with the help of the people on this forum a while back) does this well, but now I have a lot more data to parse. I think the script itself is explanatory enough to see what i'm doing. What i would like to do is cut it down to one while loop nested inside another loop so that I don't have 1600 or so elif statements. I can't figure out how to increment the output of the array. for instance, the first cycle would find the number that matches ${record1[2]} and input the url stored in ${record1[3]}. the next cycle would match ${record1[4]} and input the url in ${record1[5]}, and so on, does that make sense? The code is below and a sample .csv and text file are attached.
I have a bash variable where the content looks like this where ;f1; and ;f2; are delimiters: ;f1;field1value1;f2;field2 value1 ;f1;field1value2;f2;field2 value2 ;f1;field1value3;f2;field2 value3
So what I need is to extract and put into variables each combination of f1 and f2 in a loop to something like that:
#first pass of the loop I need: f1=field1value1 f2=field2 value1
#second pass of the loop I need: f1=field1value2 f2=field2 value2
# third pass of the loop I need: f1=field1value3 f2=field2 value3
I tried to look for this, but there are so little of perl on internet: Code: @array = [$title, $description, $pubDate, $link]; push(@feeds1, $array);
I am trying to create a 2 D array by PUSH, so the output would look like: ([ $title, $description, $pubDate, $link ], [ $title, $description, $pubDate, $link ], [ $title, $description, $pubDate, $link ], [ $title, $description, $pubDate, $link ]...etc )
I have an array called @logons. How can I step thru the array and split the fields? This is what I have so far, but doesnt work. I got the feeling I the split statement syntax is incorrect.
Code:
print @logons; foreach my $logons(@logons){ ($userid, $ip) = split(',',$logons);
[code]....
Update: Appears the data in @logons has a column header from the mysql query which I used to populate it with. So that code which I was testing does indeed work.
I am having a little trouble with a Bash shell script that I am working on. It is intended to read the information out of a gedcom genealogy file and determine who has lived in a particular area and output a report based upon who lived in a given area (like the different sections of a bygdebok for example). I am having a number of issues.
1) I can't seem to figure out how to get a variable to work as the index of an array. For example, I am trying to use the variable $individual to count which individual is being read in from the .ged file, and once that is figured out, next I will read in the individual's name, so I would like to create an array of names using the variable
Code: $individual as the index of the array. However, if I try the code Code: name[$individual]=$lineoftext;
[Code]....
I included only the last few lines of output as to not take up too much space because the output goes on forever, but you get the point from the example. This output has nothing to do with what the final output of the program is intended to be like. It is merely a test to prove that the 2 variables in question are getting their date loaded in properly.
I had a question about threads and mutexes recently answered and a members' answer sparked a different problem.'Nominal Animal' in the post mentioned said I should hold a mutex only long enough to copy my data to a temporary variable and then output by reading that temp. Here's some code on this. I must be copying the array of structs wrong because when the gui thread reads the temp copy, I end up with lots of garbage. Even running through gdb verifies that different data is in the temp array-copy than in the original.How do I go about copying this array of structs to another variable correctly in the gui thread?
So I need everything between each name, but I am not guaranteed that each time I match a name that I will have the same amount of lines, so I do a range pattern search line this to get all lines, no matter if there is 5 or 10 or 15. I simply do a loop that goes through the whole array until I hit the match, and this is my search pattern.
This works perfectly... until I hit the end and it doesn't get its final pattern match because it's at the end and there is no next entry with a (Address) line. So as a 'hack', I ended up inserting a final scalar at the end of the array that just says (Address) so it knows it's at the end. Ideally though, I'd like to do an "or" statement that says search for Address || return true if I hit the end of the array. How would I match on "End Of Array" essentially?
