What is echo in assembly language?

echo is a Unix utility that prints its arguments to standard output. printenv is a Unix utility that prints the environment to standard output. The core functionality of these programs can be written in a few lines of C, where program arguments and the environment are passed as function arguments to main.

What does int 21h mean in assembly language?

int 21h means, call the interrupt handler 0x21 which is the DOS Function dispatcher. the “mov ah,01h” is setting AH with 0x01, which is the Keyboard Input with Echo handler in the interrupt.

How is string stored in assembly?

A string is stored as consecutive characters in memory. If it’s ASCII (not UTF-8), each character is a single byte. So you can access them one at a time with byte loads/stores, like movzbl 2(\%rsi), \%eax to get the 3rd character, if rsi points to the start of the string.

How do you repeat instructions in assembly language?

Each of the above instruction has a byte, word, and doubleword version, and string instructions can be repeated by using a repetition prefix. These instructions use the ES:DI and DS:SI pair of registers, where DI and SI registers contain valid offset addresses that refers to bytes stored in memory.

Where is the first character of a string read from?

The data is read into memory starting at the address of String1. There is a null byte (0) after the last input character. So if after your call ReadString, you write mov edx,offset String1, then EDX is pointing to the first character of the string.

What are the instructions for string processing?

For 32-bit segments, string instructions use ESI and EDI registers to point to the source and destination operands, respectively. For 16-bit segments, however, the SI and the DI registers are used to point to the source and destination, respectively. There are five basic instructions for processing strings. They are −