You can abbreviate a gdb command to the first few letters of the command
name, if that abbreviation is unambiguous; and you can repeat certain
gdb commands by typing just [RET]. You can also use the [TAB]
key to get gdb to fill out the rest of a word in a command (or to
show you the alternatives available, if there is more than one possibility).
5.1. Command syntax
A gdb command is a single line of input. There is no limit on
how long it can be. It starts with a command name, which is followed by
arguments whose meaning depends on the command name. For example, the
command step accepts an argument which is the number of times to
step, as in step 5. You can also use the step command
with no arguments. Some commands do not allow any arguments.
gdb command names may always be truncated if that abbreviation is
unambiguous. Other possible command abbreviations are listed in the
documentation for individual commands. In some cases, even ambiguous
abbreviations are allowed; for example, s is specially defined as
equivalent to step even though there are other commands whose
names start with s. You can test abbreviations by using them as
arguments to the help command.
A blank line as input to gdb (typing just [RET]) means to
repeat the previous command. Certain commands (for example, run)
will not repeat this way; these are commands whose unintentional
repetition might cause trouble and which you are unlikely to want to
The list and x commands, when you repeat them with
[RET], construct new arguments rather than repeating
exactly as typed. This permits easy scanning of source or memory.
gdb can also use [RET] in another way: to partition lengthy
output, in a way similar to the common utility more
(refer to Section 21.4 Screen size). Since it is easy to press one
[RET] too many in this situation, gdb disables command
repetition after any command that generates this sort of display.
Any text from a # to the end of the line is a comment; it does
nothing. This is useful mainly in command files (refer to Section 22.3 Command files).
The C-o binding is useful for repeating a complex sequence of
commands. This command accepts the current line, like RET, and
then fetches the next line relative to the current line from the history