ASCII – Difference Between EOT and EOF

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I understand that EOT is ASCII code 4, whereas EOF is encoded as -1 (at least in C). Before I found out that EOF is mapped to -1, I thought it was just a synonym for EOT. Why is EOF mapped to -1 rather than EOT? As far as I can tell, they both do the same thing, which is to terminate a file stream. The only difference I can discern is that EOT also terminates a command in the bash shell. I would like a description of the precise technical differences between these two codes.

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Generally, EOF isn't a character; it's the absence of a character.

If a program runs on a terminal in canonical mode with default settings (i.e. a plain C program that just uses stdio), it will never see the ASCII character EOT. The terminal driver recognizes that character and creates an EOF condition (which at the low level is a 0 return value from read()). The stdio library translates that EOF condition into the return value that is appropriate for the function in question (the EOF macro for getchar(), a null pointer for fgets(), etc.)

The numeric value of the EOF macro is of no relevance anywhere but in the C library, and it shouldn't influence your understanding of the meaning of the EOF condition.

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Bash – ASCII to Binary and Binary to ASCII conversion tools

$ echo AB | perl -lpe '$_=unpack"B*"'
0100000101000010
$ echo 0100000101000010 | perl -lpe '$_=pack"B*",$_'
AB

-e expression evaluate the given expression as perl code
-p: sed mode. The expression is evaluated for each line of input, with the content of the line stored in the $_ variable and printed after the evaluation of the expression.
-l: even more like sed: instead of the full line, only the content of the line (that is, without the line delimiter) is in $_ (and a newline is added back on output). So perl -lpe code works like sed code except that it's perl code as opposed to sed code.
unpack "B*" works on the $_ variable by default and extracts its content as a bit string walking from the highest bit of the first byte to the lowest bit of the last byte.
pack does the reverse of unpack. See perldoc -f pack for details.

With spaces:

$ echo AB | perl -lpe '$_=join " ", unpack"(B8)*"'
01000001 01000010
$ echo 01000001 01000010 | perl -lape '$_=pack"(B8)*",@F'
AB

(it assumes the input is in blocks of 8 bits (0-padded)).

With unpack "(B8)*", we extract 8 bits at a time, and we join the resulting strings with spaces with join " ".

Terminal – Are ASCII Escape Sequences and Control Characters Standardized?

I wrote a document in 1984 that summarizes ANSI Codes X3.64-1979, ANSI X3.4-1977, and ANSI X3.41-1974. This ansicode.txt describes how the control codes affect DEC LA-series hardcopy terminals and the VT-series video terminals.

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Bash – ASCII to Binary and Binary to ASCII conversion tools

Terminal – Are ASCII Escape Sequences and Control Characters Standardized?

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