Debugging with GDB (February 2008)

258 Debugging with GDB
18.4 Commands for controlled output
During the execution of a command file or a user-defined command, normal GDB output
is suppressed; the only output that appears is what is explicitly printed by the commands
in the definition. This section describes three commands useful for generating exactly the
output you want.
echo text
Print text. Nonprinting characters can be included in text using C escape se-
quences, such as ‘\n’ to print a newline. No newline is printed unless you specify
one. In addition to the standard C escape sequences, a backslash followed by a
space stands for a space. This is useful for displaying a string with spaces at the
beginning or the end, since leading and trailing spaces are otherwise trimmed
from all arguments. To print ‘ and foo = ’, use the command ‘echo \ and foo
= \ ’.
A backslash at the end of text can be used, as in C, to continue the command
onto subsequent lines. For example,
echo This is some text\n\
which is continued\n\
onto several lines.\n
produces the same output as
echo This is some text\n
echo which is continued\n
echo onto several lines.\n
output expression
Print the value of expression and nothing but that value: no newlines, no
‘$nn = ’. The value is not entered in the value history either. See
Section 8.1
[Expressions], page 63, for more information on expressions.
output/fmt expression
Print the value of expression in format fmt. You can use the same formats as
for print. See Section 8.4 [Output formats], page 66, for more information.
printf string, expressions ...
Print the values of the expressions under the control of string. The expressions
are separated by commas and may be either numbers or pointers. Their values
are printed as specified by string, exactly as if your program were to execute
the C subroutine
printf (string, expressions ...);
For example, you can print two values in hex like this:
printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
The only backslash-escape sequences that you can use in the format string are
the simple ones that consist of backslash followed by a letter.