In redirection, which stream number corresponds to standard input (STDIN)?

In redirection, which stream number corresponds to standard input (STDIN)?

• A. 0
• B. 1
• C. 2
• D. 3

Answer: (A)

File descriptors map the standard streams to specific numbers: standard input, standard output, and standard error are 0, 1, and 2 respectively. Because of this mapping, standard input is the descriptor 0, which is why redirection for input uses 0 (or the shorthand <). This is the basis for commands that read input from a file, such as 0< file or the common < file syntax. The other streams use 1 for STDOUT and 2 for STDERR, so output redirection affects 1 and error redirection targets 2. In short, STDIN corresponds to the number 0.

File descriptors map the standard streams to specific numbers: standard input, standard output, and standard error are 0, 1, and 2 respectively. Because of this mapping, standard input is the descriptor 0, which is why redirection for input uses 0 (or the shorthand <). This is the basis for commands that read input from a file, such as 0< file or the common < file syntax. The other streams use 1 for STDOUT and 2 for STDERR, so output redirection affects 1 and error redirection targets 2. In short, STDIN corresponds to the number 0.