The following environment variables shall affect the execution of
sh:
ENV This variable, when and only when an interactive shell
is invoked, shall be subjected to parameter expansion
(see Section 2.6.2, Parameter Expansion) by the shell,
and the resulting value shall be used as a pathname of
a file containing shell commands to execute in the
current environment. The file need not be executable.
If the expanded value of ENV is not an absolute
pathname, the results are unspecified. ENV shall be
ignored if the real and effective user IDs or real and
effective group IDs of the process are different.
FCEDIT This variable, when expanded by the shell, shall
determine the default value for the -e editor option's
editor option-argument. If FCEDIT is null or unset, ed
shall be used as the editor.
HISTFILE Determine a pathname naming a command history file. If
the HISTFILE variable is not set, the shell may attempt
to access or create a file .sh_history in the directory
referred to by the HOME environment variable. If the
shell cannot obtain both read and write access to, or
create, the history file, it shall use an unspecified
mechanism that allows the history to operate properly.
(References to history ``file'' in this section shall
be understood to mean this unspecified mechanism in
such cases.) An implementation may choose to access
this variable only when initializing the history file;
this initialization shall occur when fc or sh first
attempt to retrieve entries from, or add entries to,
the file, as the result of commands issued by the user,
the file named by the ENV variable, or implementation-
defined system start-up files. Implementations may
choose to disable the history list mechanism for users
with appropriate privileges who do not set HISTFILE;
the specific circumstances under which this occurs are
implementation-defined. If more than one instance of
the shell is using the same history file, it is
unspecified how updates to the history file from those
shells interact. As entries are deleted from the
history file, they shall be deleted oldest first. It is
unspecified when history file entries are physically
removed from the history file.
HISTSIZE Determine a decimal number representing the limit to
the number of previous commands that are accessible. If
this variable is unset, an unspecified default greater
than or equal to 128 shall be used. The maximum number
of commands in the history list is unspecified, but
shall be at least 128. An implementation may choose to
access this variable only when initializing the history
file, as described under HISTFILE. Therefore, it is
unspecified whether changes made to HISTSIZE after the
history file has been initialized are effective.
HOME Determine the pathname of the user's home directory.
The contents of HOME are used in tilde expansion as
described in Section 2.6.1, Tilde Expansion.
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base
Definitions volume of POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of
internationalization variables used to determine the
values of locale categories.)
LC_ALL If set to a non-empty string value, override the values
of all the other internationalization variables.
LC_COLLATE
Determine the behavior of range expressions,
equivalence classes, and multi-character collating
elements within pattern matching.
LC_CTYPE Determine the locale for the interpretation of
sequences of bytes of text data as characters (for
example, single-byte as opposed to multi-byte
characters in arguments and input files), which
characters are defined as letters (character class
alpha), and the behavior of character classes within
pattern matching.
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
MAIL Determine a pathname of the user's mailbox file for
purposes of incoming mail notification. If this
variable is set, the shell shall inform the user if the
file named by the variable is created or if its
modification time has changed. Informing the user shall
be accomplished by writing a string of unspecified
format to standard error prior to the writing of the
next primary prompt string. Such check shall be
performed only after the completion of the interval
defined by the MAILCHECK variable after the last such
check. The user shall be informed only if MAIL is set
and MAILPATH is not set.
MAILCHECK
Establish a decimal integer value that specifies how
often (in seconds) the shell shall check for the
arrival of mail in the files specified by the MAILPATH
or MAIL variables. The default value shall be 600
seconds. If set to zero, the shell shall check before
issuing each primary prompt.
MAILPATH Provide a list of pathnames and optional messages
separated by <colon> characters. If this variable is
set, the shell shall inform the user if any of the
files named by the variable are created or if any of
their modification times change. (See the preceding
entry for MAIL for descriptions of mail arrival and
user informing.) Each pathname can be followed by '%'
and a string that shall be subjected to parameter
expansion and written to standard error when the
modification time changes. If a '%' character in the
pathname is preceded by a <backslash>, it shall be
treated as a literal '%' in the pathname. The default
message is unspecified.
The MAILPATH environment variable takes precedence over
the MAIL variable.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
PATH Establish a string formatted as described in the Base
Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, used to effect command
interpretation; see Section 2.9.1.1, Command Search and
Execution.
PWD This variable shall represent an absolute pathname of
the current working directory. Assignments to this
variable may be ignored.
