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authorCameron Katri <me@cameronkatri.com>2021-05-09 14:20:58 -0400
committerCameron Katri <me@cameronkatri.com>2021-05-09 14:20:58 -0400
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+.\" Copyright (c) 1980, 1990, 1993
+.\" The Regents of the University of California. All rights reserved.
+.\"
+.\" This code is derived from software contributed to Berkeley by
+.\" the Institute of Electrical and Electronics Engineers, Inc.
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\" notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\" notice, this list of conditions and the following disclaimer in the
+.\" documentation and/or other materials provided with the distribution.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\" may be used to endorse or promote products derived from this software
+.\" without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\" From @(#)printenv.1 8.1 (Berkeley) 6/6/93
+.\" From FreeBSD: src/usr.bin/printenv/printenv.1,v 1.17 2002/11/26 17:33:35 ru Exp
+.\" $FreeBSD$
+.\"
+.Dd April 17, 2008
+.Dt ENV 1
+.Os
+.Sh NAME
+.Nm env
+.Nd set environment and execute command, or print environment
+.Sh SYNOPSIS
+.Nm
+.Op Fl iv
+.Op Fl P Ar altpath
+.Op Fl S Ar string
+.Op Fl u Ar name
+.Op Ar name Ns = Ns Ar value ...
+.Op Ar utility Op Ar argument ...
+.Sh DESCRIPTION
+The
+.Nm
+utility executes another
+.Ar utility
+after modifying the environment as
+specified on the command line.
+Each
+.Ar name Ns = Ns Ar value
+option specifies the setting of an environment variable,
+.Ar name ,
+with a value of
+.Ar value .
+All such environment variables are set before the
+.Ar utility
+is executed.
+.Pp
+The options are as follows:
+.Bl -tag -width indent
+.It Fl i
+Execute the
+.Ar utility
+with only those environment variables specified by
+.Ar name Ns = Ns Ar value
+options.
+The environment inherited
+by
+.Nm
+is ignored completely.
+.\" -P
+.It Fl P Ar altpath
+Search the set of directories as specified by
+.Ar altpath
+to locate the specified
+.Ar utility
+program, instead of using the value of the
+.Ev PATH
+environment variable.
+.\" -S
+.It Fl S Ar string
+Split apart the given
+.Ar string
+into multiple strings, and process each of the resulting strings
+as separate arguments to the
+.Nm
+utility.
+The
+.Fl S
+option recognizes some special character escape sequences and
+also supports environment-variable substitution, as described
+below.
+.\" -u
+.It Fl u Ar name
+If the environment variable
+.Ar name
+is in the environment, then remove it before processing the
+remaining options.
+This is similar to the
+.Ic unset
+command in
+.Xr sh 1 .
+The value for
+.Ar name
+must not include the
+.Ql =
+character.
+.\" -v
+.It Fl v
+Print verbose information for each step of processing done by the
+.Nm
+utility.
+Additional information will be printed if
+.Fl v
+is specified multiple times.
+.El
+.Pp
+The above options are only recognized when they are specified
+before any
+.Ar name Ns = Ns Ar value
+options.
+.Pp
+If no
+.Ar utility
+is specified,
+.Nm
+prints out the names and values
+of the variables in the environment, with one name/value pair per line.
+.\"
+.Ss Details of Fl S Ss (split-string) processing
+The processing of the
+.Fl S
+option will split the given
+.Ar string
+into separate arguments based on any space or <tab> characters found in the
+.Ar string .
+Each of those new arguments will then be treated as if it had been
+specified as a separate argument on the original
+.Nm
+command.
+.Pp
+Spaces and tabs may be embedded in one of those new arguments by using
+single
+.Pq Dq Li '
+or double
+.Pq Ql \&"
+quotes, or backslashes
+.Pq Ql \e .
+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
+.Ar string
+is reached before the matching quote character.
+.Pp
+If
+.Fl S
+would create a new argument that starts with the
+.Ql #
+character, then that argument and the remainder of the
+.Ar string
+will be ignored.
+The
+.Ql \e#
+sequence can be used when you want a new argument to start
+with a
+.Ql #
+character, without causing the remainder of the
+.Ar string
+to be skipped.
+.Pp
+While processing the
+.Ar string
+value,
+.Fl 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:
+.Pp
+.Bl -tag -width indent -offset indent -compact
+.It Cm \ec
+Ignore the remaining characters in the
+.Ar string .
+This must not appear inside a double-quoted string.
+.It Cm \ef
+Replace with a <form-feed> character.
+.It Cm \en
+Replace with a <new-line> character.
+.It Cm \er
+Replace with a <carriage return> character.
+.It Cm \et
+Replace with a <tab> character.
+.It Cm \ev
+Replace with a <vertical tab> character.
+.It Cm \e#
+Replace with a
+.Ql #
+character.
+This would be useful when you need a
+.Ql #
+as the first character in one of the arguments created
+by splitting apart the given
+.Ar string .
+.It Cm \e$
+Replace with a
+.Ql $
+character.
+.It Cm \e_
+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
+.Ar string .
+.It Cm \e"
+Replace with a <double quote> character.
+.It Cm \e\'
+Replace with a <single quote> character.
+.It Cm \e\e
+Replace with a backslash character.
+.El
+.Pp
+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
+.Ql \e
+character is followed by a character other than the ones listed above.
+.Pp
+The processing of
+.Fl S
+also supports substitution of values from environment variables.
+To do this, the name of the environment variable must be inside of
+.Ql ${} ,
+such as:
+.Li ${SOMEVAR} .
+The common shell syntax of
+.Li $SOMEVAR
+is not supported.
+All values substituted will be the values of the environment variables
+as they were when the
+.Nm
+utility was originally invoked.
+Those values will not be checked for any of the escape sequences as
+described above.
+And any settings of
+.Ar name Ns = Ns Ar value
+will not effect the values used for substitution in
+.Fl S
+processing.
+.Pp
+Also,
+.Fl S
+processing can not reference the value of the special parameters
+which are defined by most shells.
+For instance,
+.Fl S
+can not recognize special parameters such as:
+.Ql $* ,
+.Ql $@ ,
+.Ql $# ,
+.Ql $?
+or
+.Ql $$
+if they appear inside the given
+.Ar string .
+.\"
+.Ss Use in shell-scripts
+The
+.Nm
+utility is often used as the
+.Ar interpreter
+on the first line of interpreted scripts, as
+described in
+.Xr execve 2 .
+.Pp
+Note that the way the kernel parses the
+.Ql #!
+(first line) of an interpreted script has changed as of
+.Fx 6.0 .
+Prior to that, the
+.Fx
+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
+.Pa /usr/local/bin/someport
+had a first line of:
+.Pp
+.Dl "#!/usr/local/bin/php -n -q -dsafe_mode=0"
+.Pp
+then the
+.Pa /usr/local/bin/php
+program would have been started with the arguments of:
+.Bd -literal -offset indent
+arg[0] = '/usr/local/bin/php'
+arg[1] = '-n'
+arg[2] = '-q'
+arg[3] = '-dsafe_mode=0'
+arg[4] = '/usr/local/bin/someport'
+.Ed
+.Pp
+plus any arguments the user specified when executing
+.Pa someport .
+However, this processing of multiple options on the
+.Ql #!
+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
+.Fx 6.0
+release, that script will result in
+.Pa /usr/local/bin/php
+being started with the arguments of:
+.Bd -literal -offset indent
+arg[0] = '/usr/local/bin/php'
+arg[1] = '-n -q -dsafe_mode=0'
+arg[2] = '/usr/local/bin/someport'
+.Ed
+.Pp
+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
+.Fx 6.0
+as it did under earlier releases, the first line should be
+changed to:
+.Pp
+.Dl "#!/usr/bin/env -S /usr/local/bin/php -n -q -dsafe_mode=0"
+.Pp
+The
+.Nm
+utility will be started with the entire line as a single
+argument:
+.Pp
+.Dl "arg[1] = '-S /usr/local/bin/php -n -q -dsafe_mode=0'"
+.Pp
+and then
+.Fl S
+processing will split that line into separate arguments before
+executing
+.Pa /usr/local/bin/php .
+.\"
+.Sh ENVIRONMENT
+The
+.Nm
+utility uses the
+.Ev PATH
+environment variable to locate the requested
+.Ar utility
+if the name contains no
+.Ql /
+characters, unless the
+.Fl P
+option has been specified.
+.Sh EXIT STATUS
+.Ex -std
+An exit status of 126 indicates that
+.Ar utility
+was found, but could not be executed.
+An exit status of 127 indicates that
+.Ar utility
+could not be found.
+.Sh EXAMPLES
+Since the
+.Nm
+utility is often used as part of the first line of an interpreted script,
+the following examples show a number of ways that the
+.Nm
+utility can be useful in scripts.
+.Pp
+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
+.Pp
+.Dl #!/usr/local/bin/foo
+and
+.Dl "#!/usr/bin/env /usr/local/bin/foo"
+.Pp
+is that the latter works even if
+.Pa /usr/local/bin/foo
+is itself an interpreted script.
+.Pp
+Probably the most common use of
+.Nm
+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
+.Ql perl
+interpreter by searching through the directories specified by
+.Ev PATH .
+.Pp
+.Dl "#!/usr/bin/env perl"
+.Pp
+One limitation of that example is that it assumes the user's value
+for
+.Ev PATH
+is set to a value which will find the interpreter you want
+to execute.
+The
+.Fl P
+option can be used to make sure a specific list of directories is
+used in the search for
+.Ar utility .
+Note that the
+.Fl S
+option is also required for this example to work correctly.
+.Pp
+.Dl "#!/usr/bin/env -S -P/usr/local/bin:/usr/bin perl"
+.Pp
+The above finds
+.Ql perl
+only if it is in
+.Pa /usr/local/bin
+or
+.Pa /usr/bin .
+That could be combined with the present value of
+.Ev PATH ,
+to provide more flexibility.
+Note that spaces are not required between the
+.Fl S
+and
+.Fl P
+options:
+.Pp
+.Dl "#!/usr/bin/env -S-P/usr/local/bin:/usr/bin:${PATH} perl"
+.Sh COMPATIBILITY
+The
+.Nm
+utility accepts the
+.Fl
+option as a synonym for
+.Fl i .
+.Sh SEE ALSO
+.Xr printenv 1 ,
+.Xr sh 1 ,
+.Xr execvp 3 ,
+.Xr environ 7
+.Sh STANDARDS
+The
+.Nm
+utility conforms to
+.St -p1003.1-2001 .
+The
+.Fl P , S , u
+and
+.Fl v
+options are non-standard extensions supported by
+.Fx ,
+but which may not be available on other operating systems.
+.Sh HISTORY
+The
+.Nm
+command appeared in
+.Bx 4.4 .
+The
+.Fl P , S
+and
+.Fl v
+options were added in
+.Fx 6.0 .
+.Sh BUGS
+The
+.Nm
+utility does not handle values of
+.Ar utility
+which have an equals sign
+.Pq Ql =
+in their name, for obvious reasons.
+.Pp
+The
+.Nm
+utility does not take multibyte characters into account when
+processing the
+.Fl S
+option, which may lead to incorrect results in some locales.