env: Run a command in a modified environment
env runs a command with a modified environment. Synopses:
env [option]… [name=value]… [command [args]…] env
Operands of the form ‘variable=value’ set the environment variable variable to value value. value may be empty (‘variable=’). Setting a variable to an empty value is different from unsetting it. These operands are evaluated left-to-right, so if two operands mention the same variable the earlier is ignored.
Environment variable names can be empty, and can contain any characters other than ‘=’ and ASCII NUL. However, it is wise to limit yourself to names that consist solely of underscores, digits, and ASCII letters, and that begin with a non-digit, as applications like the shell do not work well with other names.
The first operand that does not contain the character ‘=’
specifies the program to invoke; it is
searched for according to the
PATH environment variable. Any
remaining arguments are passed as arguments to that program.
The program should not be a special built-in utility
(see Special built-in utilities).
PATH take effect prior to searching for
command. Use caution when reducing
PATH; behavior is
not portable when
PATH is undefined or omits key directories
such as /bin.
In the rare case that a utility contains a ‘=’ in the name, the
only way to disambiguate it from a variable assignment is to use an
intermediate command for command, and pass the problematic
program name via args. For example, if ./prog= is an
executable in the current
env prog= true # runs 'true', with prog= in environment env ./prog= true # runs 'true', with ./prog= in environment env -- prog= true # runs 'true', with prog= in environment env sh -c '\prog= true' # runs 'prog=' with argument 'true' env sh -c 'exec "$@"' sh prog= true # also runs 'prog='
If no command name is specified following the environment
specifications, the resulting environment is printed. This is like
For some examples, suppose the environment passed to
contains ‘LOGNAME=rms’, ‘EDITOR=emacs’, and
$ env | LC_ALL=C sort EDITOR=emacs LOGNAME=rms PATH=.:/gnubin:/hacks
foowith a reduced environment, preserving only the original
PATHto avoid problems in locating
env - PATH="$PATH" foo
foowith the environment containing ‘LOGNAME=rms’, ‘EDITOR=emacs’, and ‘PATH=.:/gnubin:/hacks’, and guarantees that
foowas found in the file system rather than as a shell built-in.
nemacswith the environment containing ‘LOGNAME=foo’, ‘EDITOR=emacs’, ‘PATH=.:/gnubin:/hacks’, and ‘DISPLAY=gnu:0’.
env DISPLAY=gnu:0 LOGNAME=foo nemacs
/energy/--(as that is the only possible path search result); if the command exists, the environment will contain ‘LOGNAME=rms’ and ‘PATH=/energy’, and the arguments will be ‘e=mc2’, ‘bar’, and ‘baz’.
env -u EDITOR PATH=/energy -- e=mc2 bar baz
The program accepts the following options. Also see Common options. Options must precede operands.
Output a zero byte (ASCII NUL) at the end of each line, rather than a newline. This option enables other programs to parse the output even when that output would contain data with embedded newlines.
Remove variable name from the environment, if it was in the environment.
Start with an empty environment, ignoring the inherited environment.
Change the working directory to dir before invoking command.
This differs from the shell built-in
cd in that it starts
command as a subprocess rather than altering the shell’s own working
directory; this allows it to be chained with other commands that run commands
in a different context. For example:
# Run 'true' with /chroot as its root directory and /srv as its working # directory. chroot /chroot env --chdir=/srv true # Run 'true' with /build as its working directory, FOO=bar in its # environment, and a time limit of five seconds. env --chdir=/build FOO=bar timeout 5 true
0 if no command is specified and the environment is output 125 if
envitself fails 126 if command is found but cannot be invoked 127 if command cannot be found the exit status of command otherwise