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| <h4 class="subsection">25.4.2 Standard Environment Variables</h4> |
| |
| <p><a name="index-standard-environment-variables-3109"></a> |
| These environment variables have standard meanings. This doesn't mean |
| that they are always present in the environment; but if these variables |
| <em>are</em> present, they have these meanings. You shouldn't try to use |
| these environment variable names for some other purpose. |
| |
| <!-- Extra blank lines make it look better. --> |
| <dl> |
| <dt><code>HOME</code><dd><a name="index-g_t_0040code_007bHOME_007d-environment-variable-3110"></a><a name="index-home-directory-3111"></a> |
| This is a string representing the user's <dfn>home directory</dfn>, or |
| initial default working directory. |
| |
| <p>The user can set <code>HOME</code> to any value. |
| If you need to make sure to obtain the proper home directory |
| for a particular user, you should not use <code>HOME</code>; instead, |
| look up the user's name in the user database (see <a href="User-Database.html#User-Database">User Database</a>). |
| |
| <p>For most purposes, it is better to use <code>HOME</code>, precisely because |
| this lets the user specify the value. |
| |
| <!-- !!! also USER --> |
| <br><dt><code>LOGNAME</code><dd><a name="index-g_t_0040code_007bLOGNAME_007d-environment-variable-3112"></a> |
| This is the name that the user used to log in. Since the value in the |
| environment can be tweaked arbitrarily, this is not a reliable way to |
| identify the user who is running a program; a function like |
| <code>getlogin</code> (see <a href="Who-Logged-In.html#Who-Logged-In">Who Logged In</a>) is better for that purpose. |
| |
| <p>For most purposes, it is better to use <code>LOGNAME</code>, precisely because |
| this lets the user specify the value. |
| |
| <br><dt><code>PATH</code><dd><a name="index-g_t_0040code_007bPATH_007d-environment-variable-3113"></a> |
| A <dfn>path</dfn> is a sequence of directory names which is used for |
| searching for a file. The variable <code>PATH</code> holds a path used |
| for searching for programs to be run. |
| |
| <p>The <code>execlp</code> and <code>execvp</code> functions (see <a href="Executing-a-File.html#Executing-a-File">Executing a File</a>) |
| use this environment variable, as do many shells and other utilities |
| which are implemented in terms of those functions. |
| |
| <p>The syntax of a path is a sequence of directory names separated by |
| colons. An empty string instead of a directory name stands for the |
| current directory (see <a href="Working-Directory.html#Working-Directory">Working Directory</a>). |
| |
| <p>A typical value for this environment variable might be a string like: |
| |
| <pre class="smallexample"> :/bin:/etc:/usr/bin:/usr/new/X11:/usr/new:/usr/local/bin |
| </pre> |
| <p>This means that if the user tries to execute a program named <code>foo</code>, |
| the system will look for files named <samp><span class="file">foo</span></samp>, <samp><span class="file">/bin/foo</span></samp>, |
| <samp><span class="file">/etc/foo</span></samp>, and so on. The first of these files that exists is |
| the one that is executed. |
| |
| <!-- !!! also TERMCAP --> |
| <br><dt><code>TERM</code><dd><a name="index-g_t_0040code_007bTERM_007d-environment-variable-3114"></a> |
| This specifies the kind of terminal that is receiving program output. |
| Some programs can make use of this information to take advantage of |
| special escape sequences or terminal modes supported by particular kinds |
| of terminals. Many programs which use the termcap library |
| (see <a href="../termcap/Finding-a-Terminal-Description.html#Finding-a-Terminal-Description">Find</a>) use the <code>TERM</code> environment variable, for example. |
| |
| <br><dt><code>TZ</code><dd><a name="index-g_t_0040code_007bTZ_007d-environment-variable-3115"></a> |
| This specifies the time zone. See <a href="TZ-Variable.html#TZ-Variable">TZ Variable</a>, for information about |
| the format of this string and how it is used. |
| |
| <br><dt><code>LANG</code><dd><a name="index-g_t_0040code_007bLANG_007d-environment-variable-3116"></a> |
| This specifies the default locale to use for attribute categories where |
| neither <code>LC_ALL</code> nor the specific environment variable for that |
| category is set. See <a href="Locales.html#Locales">Locales</a>, for more information about |
| locales. |
| |
| <br><dt><code>LC_ALL</code><dd><a name="index-g_t_0040code_007bLC_005fALL_007d-environment-variable-3117"></a> |
| If this environment variable is set it overrides the selection for all |
| the locales done using the other <code>LC_*</code> environment variables. The |
| value of the other <code>LC_*</code> environment variables is simply ignored |
| in this case. |
| |
| <br><dt><code>LC_COLLATE</code><dd><a name="index-g_t_0040code_007bLC_005fCOLLATE_007d-environment-variable-3118"></a> |
| This specifies what locale to use for string sorting. |
| |
| <br><dt><code>LC_CTYPE</code><dd><a name="index-g_t_0040code_007bLC_005fCTYPE_007d-environment-variable-3119"></a> |
| This specifies what locale to use for character sets and character |
| classification. |
| |
| <br><dt><code>LC_MESSAGES</code><dd><a name="index-g_t_0040code_007bLC_005fMESSAGES_007d-environment-variable-3120"></a> |
| This specifies what locale to use for printing messages and to parse |
| responses. |
| |
| <br><dt><code>LC_MONETARY</code><dd><a name="index-g_t_0040code_007bLC_005fMONETARY_007d-environment-variable-3121"></a> |
| This specifies what locale to use for formatting monetary values. |
| |
| <br><dt><code>LC_NUMERIC</code><dd><a name="index-g_t_0040code_007bLC_005fNUMERIC_007d-environment-variable-3122"></a> |
| This specifies what locale to use for formatting numbers. |
| |
| <br><dt><code>LC_TIME</code><dd><a name="index-g_t_0040code_007bLC_005fTIME_007d-environment-variable-3123"></a> |
| This specifies what locale to use for formatting date/time values. |
| |
| <br><dt><code>NLSPATH</code><dd><a name="index-g_t_0040code_007bNLSPATH_007d-environment-variable-3124"></a> |
| This specifies the directories in which the <code>catopen</code> function |
| looks for message translation catalogs. |
| |
| <br><dt><code>_POSIX_OPTION_ORDER</code><dd><a name="index-g_t_0040code_007b_005fPOSIX_005fOPTION_005fORDER_007d-environment-variable_002e-3125"></a> |
| If this environment variable is defined, it suppresses the usual |
| reordering of command line arguments by <code>getopt</code> and |
| <code>argp_parse</code>. See <a href="Argument-Syntax.html#Argument-Syntax">Argument Syntax</a>. |
| |
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