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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 first case, stderr is redirected to a file named ' 1 ' and in the second, stderr is redirected to stdout. Another useful capability is to redirect one standard file handle to another.
#!/usr/bin/env python import sys # Save the current stdout so that we can revert sys.stdout # after we complete our redirection stdin_fileno = sys. stdin stdout_fileno = sys. stdout # Redirect sys.stdout to the file sys. stdout = open ("myfile.txt", "w") ctr = 0 for inps in stdin_fileno: ctrs = str (ctr) # Prints to the redirected stdout sys ...
Conversely, scripting programming languages, in particular those with an eval function (such as REXX, Perl, Python, Ruby or Jython), can be used to implement command-line interpreters and filters. For a few operating systems , most notably DOS , such a command interpreter provides a more flexible command-line interface than the one supplied.
Yes (stdin, stdout, stderr, stdout+stderr) Yes (via registry, TCMD.INI / 4NT.INI file, startup parameters, environment variables, SETDOS command) Yes (automatic via registry and TCSTART / 4START as well as TCEXIT / 4EXIT, or explicitly via /K startup option) Yes (via CALL command or /C and /K startup options) Yes No VMS DCL [22] OpenVMS
>> 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. 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.
-print: always returns true; prints the name of the current file plus a newline to the stdout.-print0: always returns true; prints the name of the current file plus a null character to the stdout. Not required by POSIX.-exec program [arguments...] ;: runs program with the given arguments, and returns true if its exit status was 0, false otherwise.
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KornShell (ksh) in several possible versions such as ksh88, Korn Shell '93 and others. The Bourne shell (sh), one of the oldest shells still common in use; The C shell (csh) GNU Bash (bash) tclsh, a shell which is a main component of the Tcl/Tk programming language. The wish is a GUI-based Tcl/Tk shell.