Okay, this probably sounds dumb for anyone who knows the answer, but I'm completely lost. I have to use the head command to search a directory AND all of its subdirectories to display the first line of all .txt files. I know how to do this: head -1 ~/UnixCourse/*.txt, but that does not search the... (4 Replies)
Hi All,
How can the head command be used to extract only a particular line.
By default head -n filename displays the first n lines. I want only the nth line.
I couldn't get it from forum search.
Thanks,
Sumesh (6 Replies)
Hi friends,I am new to unix and this is really a dummy question.but please help me out.
How to simulate head command without using head command???
also tail command too,also more command.
it is given as a homework to do....please tell me how to do (2 Replies)
Hi, I have the following problem. I have files with one column of data (let's say file1.dat, file2.dat...file6.dat), and I would like to record the first value of the column of each file into another file (let's name it fileall.dat), which would have the the six values, one in each column. I use to... (4 Replies)
Hi,
I have been given assignment of 30 scripts out of which I was able to solve many, I need help with few out of which one asks to imitate head and tail command of unix without using the head and tail commands. Problem is stated below:
Write an interactive shell script to imitate the head... (5 Replies)
Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!
1. The problem statement, all variables and given/known data:
I've been stuck on this problem for 2 days now
What command would you enter to list the first lines of all text... (11 Replies)
Hi,
I need some advise on whether there is a better way of doing what I am currently planning to do. Perhaps I should be using arrays instead of re-directing output to files?
I need to use a tool/program named ADRCI provided by Oracle to remove trace files that it generates. Honestly it is... (1 Reply)
Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!
1. The problem statement, all variables and given/known data:
Write a script that allows the user to print the first n lines or the last n lines of every file in the... (18 Replies)
Discussion started by: lukefrost96
18 Replies
LEARN ABOUT DEBIAN
dispatch_apply_f
dispatch_apply(3) BSD Library Functions Manual dispatch_apply(3)NAME
dispatch_apply -- schedule blocks for iterative execution
SYNOPSIS
#include <dispatch/dispatch.h>
void
dispatch_apply(size_t iterations, dispatch_queue_t queue, void (^block)(size_t));
void
dispatch_apply_f(size_t iterations, dispatch_queue_t queue, void *context, void (*function)(void *, size_t));
DESCRIPTION
The dispatch_apply() function provides data-level concurrency through a "for (;;)" loop like primitive:
dispatch_queue_t the_queue = dispatch_get_concurrent_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT);
size_t iterations = 10;
// 'idx' is zero indexed, just like:
// for (idx = 0; idx < iterations; idx++)
dispatch_apply(iterations, the_queue, ^(size_t idx) {
printf("%zu
", idx);
});
Like a "for (;;)" loop, the dispatch_apply() function is synchronous. If asynchronous behavior is desired, please wrap the call to
dispatch_apply() with a call to dispatch_async() against another queue.
Sometimes, when the block passed to dispatch_apply() is simple, the use of striding can tune performance. Calculating the optimal stride is
best left to experimentation. Start with a stride of one and work upwards until the desired performance is achieved (perhaps using a power
of two search):
#define STRIDE 3
dispatch_apply(count / STRIDE, queue, ^(size_t idx) {
size_t j = idx * STRIDE;
size_t j_stop = j + STRIDE;
do {
printf("%zu
", j++);
} while (j < j_stop);
});
size_t i;
for (i = count - (count % STRIDE); i < count; i++) {
printf("%zu
", i);
}
FUNDAMENTALS
Conceptually, dispatch_apply() is a convenient wrapper around dispatch_async() and a semaphore to wait for completion. In practice, the dis-
patch library optimizes this function.
The dispatch_apply() function is a wrapper around dispatch_apply_f().
SEE ALSO dispatch(3), dispatch_async(3), dispatch_queue_create(3), dispatch_semaphore_create(3)Darwin May 1, 2009 Darwin