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In shells derived from csh (the C shell), the syntax instead appends the & (ampersand) character to the redirect characters, thus achieving a similar result. The reason for this is to distinguish between a file named '1' and stdout, i.e. cat file 2 >1 vs cat file 2 > & 1 .
In the case of an interactive shell, that is usually the text terminal which initiated the program. The file descriptor for standard output is 1 (one); the POSIX <unistd.h> definition is STDOUT_FILENO ; the corresponding C <stdio.h> variable is FILE* stdout ; similarly, the C++ <iostream> variable is std::cout .
Process substitution can also be used to capture output that would normally go to a file, and redirect it to the input of a process. The Bash syntax for writing to a process is >(command). Here is an example using the tee, wc and gzip commands that counts the lines in a file with wc -l and compresses it with gzip in one pass:
The Linux tee command was written by Mike Parker, Richard Stallman, and David MacKenzie. [5] The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities. [6] The FreeDOS version was developed by Jim Hall and is licensed under the GPL. [7]
>>& 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. Stdin will read the following lines up to the one that matches string. Redirecting stderr alone isn't possible without the aid of a sub-shell.
Bash can execute the vast majority of Bourne shell scripts without modification, with the exception of Bourne shell scripts stumbling into fringe syntax behavior interpreted differently in Bash or attempting to run a system command matching a newer Bash builtin, etc. Bash command syntax includes ideas drawn from the Korn Shell (ksh) and the C ...
In computing, command substitution is a facility that allows a command to be run and its output to be pasted back on the command line as arguments to another command. . Command substitution first appeared in the Bourne shell, [1] introduced with Version 7 Unix in 1979, and has remained a characteristic of all later Uni
Under Unix, devices are files too, so the normal type of file for the shell used for stdin, stdout and stderr is a tty device file. Another command-line interface allows a shell program to launch helper programs, either to launch documents or start a program.