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The test command in Unix evaluates the expression parameter. In most recent shell implementations, it is a shell builtin, even though the external version still exists.In the second form of the command, the [ ] (brackets) must be surrounded by blank spaces (this is because [is a program and POSIX compatible shells require a space between the program name and its arguments).
An existence check before reading a file can catch and/or prevent a fatal error, for instance. For that reason, most programming language libraries contain a means of checking whether a file exists. An existence check can sometimes involve a " brute force " approach of checking all records for a given identifier, as in this Microsoft Excel ...
In Unix-like operating systems, find is a command-line utility that locates files based on some user-specified criteria and either prints the pathname of each matched object or, if another action is requested, performs that action on each matched object.
File URLs are rarely used in Web pages on the public Internet, since they imply that a file exists on the designated host. The host specifier can be used to retrieve a file from an external source, although no specific file-retrieval protocol is specified; and using it should result in a message that informs the user that no mechanism to access ...
While Bash was developed for UNIX and UNIX-like operating systems, such as GNU/Linux, it is also available on Android, macOS, Windows, and numerous other current and historical operating systems. [12] "Although there have been attempts to create specialized shells, the Bourne shell derivatives continue to be the primary shells in use."
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 .
>& file means both stdout and stderr will be written to file, overwriting it if it exists, and creating it if it doesn't. >> file means stdout will be appended at the end of file. >>& file means both stdout and stderr will be appended at the end of file. < file means stdin will be read from file. << string is a here document.
JP Software command-line processors provide user-configurable colorization of file and directory names in directory listings based on their file extension and/or attributes through an optionally defined %COLORDIR% environment variable. For the Unix/Linux shells, this is a feature of the ls command and the terminal.