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google_ad_section_start shm_open, shm_unlink - create/open or unlink POSIX shared memory objects #include < sys/mman.h > #include < sys/stat.h > /* For mode constants */ #include < fcntl.h > /* For O_* constants */ int shm_open(const char * name , int oflag , mode_t mode ); int shm_unlink(const char * name ); Link with -lrt . shm_open () creates and opens a new, or opens an existing, POSIX shared memory object. A POSIX shared memory object is in effect a handle which can be used by unrelated processes to mmap (2) the same region of shared memory. The shm_unlink () function performs the converse operation, removing an object previously created by shm_open (). The operation of shm_open () is analogous to that of open (2) . name specifies the shared memory object to be created or opened. For portable use, a shared memory object should be identified by a name of the ...

google_ad_section_start splice - splice data to/from a pipe #define _GNU_SOURCE /* See feature_test_macros (7) */#include < fcntl.h >ssize_t splice(int fd_in, loff_t *off_in, int fd_out, loff_t *off_out, size_t lenunsigned int " flags ); splice () moves data between two file descriptors without copying between kernel address space and user address space. It transfers up to len bytes of data from the file descriptor fd_in to the file descriptor fd_out , where one of the descriptors must refer to a pipe. If fd_in refers to a pipe, then off_in must be NULL. If fd_in does not refer to a pipe and off_in is NULL, then bytes are read from fd_in starting from the current file offset, and the current file offset is adjusted appropriately. If fd_in does not refer to a pipe and off_in is not NULL, then off_in must point to a buffer which specifies the start...

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google_ad_section_start random, urandom - kernel random number source devices #include < linux/random.h > int ioctl( fd , RND request , param ); The character special files /dev/random and /dev/urandom (present since Linux 1.3.30) provide an interface to the kernel's random number generator. File /dev/random has major device number 1 and minor device number 8. File /dev/urandom has major device number 1 and minor device number 9. The random number generator gathers environmental noise from device drivers and other sources into an entropy pool. The generator also keeps an estimate of the number of bits of noise in the entropy pool. From this entropy pool random numbers are created. When read, the /dev/random device will only return random bytes within the estimated number of bits of noise in the entropy pool. /dev/random should be suitable for uses that need very hig...

google_ad_section_start This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. pipe - create an interprocess channel #include < unistd.h > int pipe(int fildes [2]); The pipe () function shall create a pipe and place two file descriptors, one each into the arguments fildes [0] and fildes [1], that refer to the open file descriptions for the read and write ends of the pipe. Their integer values shall be the two lowest available at the time of the pipe () call. The O_NONBLOCK and FD_CLOEXEC flags shall be clear on both file descriptors. (The fcntl () function can be used to set both these flags.) Data can be written to the file descriptor fildes [1] and read from the file descriptor filde...

Advanced Bash-Scripting Guide: Prev Chapter 18. Here Documents Next A here string can be considered as a stripped-down form of a here document . It consists of nothing more than COMMAND <<<$WORD , where $WORD is expanded and fed to the stdin of COMMAND . As a simple example, consider this alternative to the echo-grep construction. # Instead of: if echo "$VAR" | grep -q txt # if [[ $VAR = *txt* ]] # etc. # Try: if grep -q "txt" <<< "$VAR" then echo "$VAR contains the substring sequence \"txt\"" fi # Thank you, Sebastian Kaminski, for the suggestion. Or, in combination with read : String="This is a string of words." read -r -a Words <<< "$String" # The -a option to "read" #+ assigns the resulting values to successive members of an array. echo "First word in String is: ${Words[0]}" # This echo "Second word in String is: ${Words[1]}" # is echo "Third word in...

google_ad_section_start open, creat - open and possibly create a file or device #include < sys/types.h >#include < sys/stat.h >#include < fcntl.h > int open(const char *pathname, int flags);int open(const char *pathname, int flags, mode_t mode);int creat(const char *pathname, mode_t mode); Given a pathname for a file, open () returns a file descriptor, a small, nonnegative integer for use in subsequent system calls ( read (2) , write (2) , lseek (2) , fcntl (2) , etc.). The file descriptor returned by a successful call will be the lowest-numbered file descriptor not currently open for the process. By default, the new file descriptor is set to remain open across an execve (2) (i.e., the FD_CLOEXEC file descriptor flag described in fcntl (2) is initially disabled; the O_CLOEXEC flag, described below, can be used to change this default). The file offset is set to the beginning...