SysTutorials Posts

bash – GNU Bourne-Again SHell Synopsisbash [options] [command_string | file] CopyrightBash is Copyright (C) 1989-2020 by the Free Software Foundation, Inc. DescriptionBash is an sh-compatible command language interpreter that executes commands read from the standard input or from a file. Bash also incorporates useful features from the Korn and C shells (ksh and csh). Bash…

strcpy, strncpy – copy a string Synopsis #include <string.h> char *strcpy(char *dest, const char *src); char *strncpy(char *dest, const char *src, size_t n); Description The strcpy() function copies the string pointed to by src, including the terminating null byte (‘\0’), to the buffer pointed to by dest. The strings may not overlap, and the destination…

write – write to a file descriptor Synopsis#include <unistd.h> ssize_t write(int fd, const void *buf, size_t count); Descriptionwrite() writes up to count bytes from the buffer starting at buf to the file referred to by the file descriptor fd. The number of bytes written may be less than count if, for example, there is insufficient…

read – read from a file descriptor Synopsis#include <unistd.h> ssize_t read(int fd, void *buf, size_t count);Descriptionread() attempts to read up to count bytes from file descriptor fd into the buffer starting at buf. On files that support seeking, the read operation commences at the file offset, and the file offset is incremented by the number…

cat – concatenate files and print on the standard output Synopsiscat [,OPTION/]… [,FILE/]… DescriptionConcatenate FILE(s) to standard output. With no FILE, or when FILE is -, read standard input. -A, –show-all equivalent to -vET -b, –number-nonblank number nonempty output lines, overrides -n -e equivalent to -vE -E, –show-ends display $ at end of each line…

stat, fstat, lstat, fstatat – get file status Synopsis#include <sys/types.h> #include <sys/stat.h> #include <unistd.h> int stat(const char *pathname, struct stat *statbuf); int fstat(int fd, struct stat *statbuf); int lstat(const char *pathname, struct stat *statbuf); #include <fcntl.h> /* Definition of AT_* constants */ #include <sys/stat.h> int fstatat(int dirfd, const char *pathname, struct stat *statbuf, int flags);Feature…

grep, egrep, fgrep, rgrep – print lines that match patterns Synopsisgrep [OPTION…] PATTERNS [FILE…] grep [OPTION…] -e PATTERNS … [FILE…] grep [OPTION…] -f PATTERN_FILE … [FILE…] Descriptiongrep searches for PATTERNS in each FILE. PATTERNS is one or more patterns separated by newline characters, and grep prints each line that matches a pattern. Typically PATTERNS should…

malloc, free, calloc, realloc, reallocarray – allocate and free dynamic memory Synopsis#include <stdlib.h> void *malloc(size_t size); void free(void *ptr); void *calloc(size_t nmemb, size_t size); void *realloc(void *ptr, size_t size); void *reallocarray(void *ptr, size_t nmemb, size_t size);Feature Test Macro Requirements for glibc (see feature_test_macros(7)): reallocarray():     Since glibc 2.29:         _DEFAULT_SOURCE     Glibc 2.28 and earlier:         _GNU_SOURCE DescriptionThe malloc()…

printf, fprintf, dprintf, sprintf, snprintf, vprintf, vfprintf, vdprintf, vsprintf, vsnprintf – formatted output conversion Synopsis#include <stdio.h> int printf(const char *format, …); int fprintf(FILE *stream, const char *format, …); int dprintf(int fd, const char *format, …); int sprintf(char *str, const char *format, …); int snprintf(char *str, size_t size, const char *format, …); #include <stdarg.h> int vprintf(const…

open, openat, creat – open and possibly create a file Synopsis#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); int openat(int dirfd, const char *pathname, int flags); int openat(int dirfd, const char *pathname, int flags, mode_t mode); /*…

ls – list directory contents Synopsisls [,OPTION/]… [,FILE/]… DescriptionList information about the FILEs (the current directory by default). Sort entries alphabetically if none of -cftuvSUX nor –sort is specified. Mandatory arguments to long options are mandatory for short options too. -a, –all do not ignore entries starting with . -A, –almost-all do not list implied…