ENV(1) General Commands Manual ENV(1)
NAME
env – set environment and execute command, or print environment
SYNOPSIS
env [-iv] [-P altpath] [-S string] [-u name] [name=value ...]
[utility [argument ...]]
DESCRIPTION
The env utility executes another utility after modifying the environment as
specified on the command line. Each name=value option specifies the
setting of an environment variable, name, with a value of value. All such
environment variables are set before the utility is executed.
The options are as follows:
-i Execute the utility with only those environment variables specified
by name=value options. The environment inherited by env is ignored
completely.
-P altpath
Search the set of directories as specified by altpath to locate the
specified utility program, instead of using the value of the PATH
environment variable.
-S string
Split apart the given string into multiple strings, and process
each of the resulting strings as separate arguments to the env
utility. The -S option recognizes some special character escape
sequences and also supports environment-variable substitution, as
described below.
-u name
If the environment variable name is in the environment, then remove
it before processing the remaining options. This is similar to the
unset command in sh(1). The value for name must not include the
‘=’ character.
-v Print verbose information for each step of processing done by the
env utility. Additional information will be printed if -v is
specified multiple times.
The above options are only recognized when they are specified before any
name=value options.
If no utility is specified, env prints out the names and values of the
variables in the environment, with one name/value pair per line.
Details of -S -Ss -(split-string) -processing
The processing of the -S option will split the given string into separate
arguments based on any space or <tab> characters found in the string. Each
of those new arguments will then be treated as if it had been specified as
a separate argument on the original env command.
Spaces and tabs may be embedded in one of those new arguments by using
single (“'”) or double (‘"’) quotes, or backslashes (‘\’). Single quotes
will escape all non-single quote characters, up to the matching single
quote. Double quotes will escape all non-double quote characters, up to
the matching double quote. It is an error if the end of the string is
reached before the matching quote character.
If -S would create a new argument that starts with the ‘#’ character, then
that argument and the remainder of the string will be ignored. The ‘\#’
sequence can be used when you want a new argument to start with a ‘#’
character, without causing the remainder of the string to be skipped.
While processing the string value, -S processing will treat certain
character combinations as escape sequences which represent some action to
take. The character escape sequences are in backslash notation. The
characters and their meanings are as follows:
\c Ignore the remaining characters in the string. This must not
appear inside a double-quoted string.
\f Replace with a <form-feed> character.
\n Replace with a <new-line> character.
\r Replace with a <carriage return> character.
\t Replace with a <tab> character.
\v Replace with a <vertical tab> character.
\# Replace with a ‘#’ character. This would be useful when you
need a ‘#’ as the first character in one of the arguments
created by splitting apart the given string.
\$ Replace with a ‘$’ character.
\_ If this is found inside of a double-quoted string, then
replace it with a single blank. If this is found outside of
a quoted string, then treat this as the separator character
between new arguments in the original string.
\" Replace with a <double quote> character.
\´ Replace with a <single quote> character.
\\ Replace with a backslash character.
The sequences for <single-quote> and backslash are the only sequences which
are recognized inside of a single-quoted string. The other sequences have
no special meaning inside a single-quoted string. All escape sequences are
recognized inside of a double-quoted string. It is an error if a single
‘\’ character is followed by a character other than the ones listed above.
The processing of -S also supports substitution of values from environment
variables. To do this, the name of the environment variable must be inside
of ‘${}’, such as: ${SOMEVAR}. The common shell syntax of $SOMEVAR is not
supported. All values substituted will be the values of the environment
variables as they were when the env utility was originally invoked. Those
values will not be checked for any of the escape sequences as described
above. And any settings of name=value will not effect the values used for
substitution in -S processing.
Also, -S processing can not reference the value of the special parameters
which are defined by most shells. For instance, -S can not recognize
special parameters such as: ‘$*’, ‘$@’, ‘$#’, ‘$?’ or ‘$$’ if they appear
inside the given string.
Use in shell-scripts
The env utility is often used as the interpreter on the first line of
interpreted scripts, as described in execve(2).
Note that the way the kernel parses the ‘#!’ (first line) of an interpreted
script has changed as of FreeBSD 6.0. Prior to that, the FreeBSD kernel
would split that first line into separate arguments based on any whitespace
(space or <tab> characters) found in the line. So, if a script named
/usr/local/bin/someport had a first line of:
#!/usr/local/bin/php -n -q -dsafe_mode=0
then the /usr/local/bin/php program would have been started with the
arguments of:
arg[0] = '/usr/local/bin/php'
arg[1] = '-n'
arg[2] = '-q'
arg[3] = '-dsafe_mode=0'
arg[4] = '/usr/local/bin/someport'
plus any arguments the user specified when executing someport. However,
this processing of multiple options on the ‘#!’ line is not the way any
other operating system parses the first line of an interpreted script. So
after a change which was made for FreeBSD 6.0 release, that script will
result in /usr/local/bin/php being started with the arguments of:
arg[0] = '/usr/local/bin/php'
arg[1] = '-n -q -dsafe_mode=0'
arg[2] = '/usr/local/bin/someport'
plus any arguments the user specified. This caused a significant change in
the behavior of a few scripts. In the case of above script, to have it
behave the same way under FreeBSD 6.0 as it did under earlier releases, the
first line should be changed to:
#!/usr/bin/env -S /usr/local/bin/php -n -q -dsafe_mode=0
The env utility will be started with the entire line as a single argument:
arg[1] = '-S /usr/local/bin/php -n -q -dsafe_mode=0'
and then -S processing will split that line into separate arguments before
executing /usr/local/bin/php.
ENVIRONMENT
The env utility uses the PATH environment variable to locate the requested
utility if the name contains no ‘/’ characters, unless the -P option has
been specified.
EXIT STATUS
The env utility exits 0 on success, and >0 if an error occurs. An exit
status of 126 indicates that utility was found, but could not be executed.
An exit status of 127 indicates that utility could not be found.
EXAMPLES
Since the env utility is often used as part of the first line of an
interpreted script, the following examples show a number of ways that the
env utility can be useful in scripts.
The kernel processing of an interpreted script does not allow a script to
directly reference some other script as its own interpreter. As a way
around this, the main difference between
#!/usr/local/bin/foo
and
#!/usr/bin/env /usr/local/bin/foo
is that the latter works even if /usr/local/bin/foo is itself an
interpreted script.
Probably the most common use of env is to find the correct interpreter for
a script, when the interpreter may be in different directories on different
systems. The following example will find the ‘perl’ interpreter by
searching through the directories specified by PATH.
#!/usr/bin/env perl
One limitation of that example is that it assumes the user's value for PATH
is set to a value which will find the interpreter you want to execute. The
-P option can be used to make sure a specific list of directories is used
in the search for utility. Note that the -S option is also required for
this example to work correctly.
#!/usr/bin/env -S -P/usr/local/bin:/usr/bin perl
The above finds ‘perl’ only if it is in /usr/local/bin or /usr/bin. That
could be combined with the present value of PATH, to provide more
flexibility. Note that spaces are not required between the -S and -P
options:
#!/usr/bin/env -S-P/usr/local/bin:/usr/bin:${PATH} perl
COMPATIBILITY
The env utility accepts the - option as a synonym for -i.
SEE ALSO
printenv(1), sh(1), execvp(3), environ(7)
STANDARDS
The env utility conforms to IEEE Std 1003.1-2001 (“POSIX.1”). The -P, -S,
-u and -v options are non-standard extensions supported by FreeBSD, but
which may not be available on other operating systems.
HISTORY
The env command appeared in 4.4BSD. The -P, -S and -v options were added
in FreeBSD 6.0.
BUGS
The env utility does not handle values of utility which have an equals sign
(‘=’) in their name, for obvious reasons.
The env utility does not take multibyte characters into account when
processing the -S option, which may lead to incorrect results in some
locales.
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