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getopt is a system dependent function, and its behavior depends on the implementation in the C library. Some custom implementations like gnulib are available, however. [6]The conventional (POSIX and BSD) handling is that the options end when the first non-option argument is encountered, and that getopt would return -1 to signal that.
Bash supports process substitution using the <(command) and >(command)syntax, which substitutes the output of (or input to) a command where a filename is normally used. (This is implemented through /proc/fd/ unnamed pipes on systems that support that, or via temporary named pipes where necessary).
A shell script can provide a convenient variation of a system command where special environment settings, command options, or post-processing apply automatically, but in a way that allows the new script to still act as a fully normal Unix command. One example would be to create a version of ls, the command to list files, giving it a shorter ...
read is a command found on Unix and Unix-like operating systems such as Linux. It reads a line of input from standard input or a file passed as an argument to its -u flag, and assigns it to a variable. It is built into shells such as Bash. [1]
getopts is a built-in Unix shell command for parsing command-line arguments. It is designed to process command line arguments that follow the POSIX Utility Syntax Guidelines, based on the C interface of getopt. The predecessor to getopts was the external program getopt by Unix System Laboratories.
Here documents are available in many Unix shells. [1] In the following example, text is passed to the tr command (transliterating lower to upper-case) using a here document. This could be in a shell file, or entered interactively at a prompt.
Wildcard completion is a generalization of path completion, where an expression matches any number of files, using any supported syntax for file matching. Variable completion is the completion of the name of a variable name (environment variable or shell variable). Bash, zsh, and fish have completion for all variable names.
A Unix shell is a command-line interpreter or shell that provides a command line user interface for Unix-like operating systems. The shell is both an interactive command language and a scripting language , and is used by the operating system to control the execution of the system using shell scripts .