4.4 Your Program's Environment

The environment consists of a set of environment variables and their values. Environment variables conventionally record such things as your user name, your home directory, your terminal type, and your search path for programs to run. Usually you set up environment variables with the shell and they are inherited by all the other programs you run. When debugging, it can be useful to try running your program with a modified environment without having to start gdb over again.

path directory

Add directory to the front of the PATH environment variable (the search path for executables) that will be passed to your program. The value of PATH used by gdb does not change. You may specify several directory names, separated by whitespace or by a system-dependent separator character (‘:’ on Unix, ‘;’ on MS-DOS and MS-Windows). If directory is already in the path, it is moved to the front, so it is searched sooner.

You can use the string ‘$cwd’ to refer to whatever is the current working directory at the time gdb searches the path. If you use ‘.’ instead, it refers to the directory where you executed the path command. gdb replaces ‘.’ in the directory argument (with the current path) before adding directory to the search path.

show paths

Display the list of search paths for executables (the PATH environment variable).

show environment [varname]

Print the value of environment variable varname to be given to your program when it starts. If you do not supply varname, print the names and values of all environment variables to be given to your program. You can abbreviate environment as env.

set environment varname [=value]

Set environment variable varname to value. The value changes for your program (and the shell gdb uses to launch it), not for gdb itself. The value may be any string; the values of environment variables are just strings, and any interpretation is supplied by your program itself. The value parameter is optional; if it is eliminated, the variable is set to a null value.

For example, this command:

          set env USER = foo

tells the debugged program, when subsequently run, that its user is named ‘foo’. (The spaces around ‘=’ are used for clarity here; they are not actually required.)

Note that on Unix systems, gdb runs your program via a shell, which also inherits the environment set with set environment. If necessary, you can avoid that by using the ‘env’ program as a wrapper instead of using set environment. See set exec-wrapper, for an example doing just that.

unset environment varname

Remove variable varname from the environment to be passed to your program. This is different from ‘set env varname =’; unset environment removes the variable from the environment, rather than assigning it an empty value.

Warning: On Unix systems, gdb runs your program using the shell indicated by your SHELL environment variable if it exists (or /bin/sh if not). If your SHELL variable names a shell that runs an initialization file when started non-interactively—such as .cshrc for C-shell, $.zshenv for the Z shell, or the file specified in the ‘BASH_ENV’ environment variable for BASH—any variables you set in that file affect your program. You may wish to move setting of environment variables to files that are only run when you sign on, such as .login or .profile.