{ "content": [ { "type": "text", "text": "# environ (man)\n\n## NAME\n\nenviron - user environment\n\n## SYNOPSIS\n\nextern char environ;\n\n## DESCRIPTION\n\nThe variable environ points to an array of pointers to strings called the \"environment\". The\nlast pointer in this array has the value NULL. This array of strings is made available to\nthe process by the execve(2) call when a new program is started. When a child process is\ncreated via fork(2), it inherits a copy of its parent's environment.\n\n## Sections\n\n- **NAME**\n- **SYNOPSIS**\n- **DESCRIPTION**\n- **NOTES**\n- **BUGS**\n- **SEE ALSO**\n\nUse structuredContent.sections for detailed options, examples, and full documentation.\n" } ], "structuredContent": { "command": "environ", "section": "", "mode": "man", "summary": "environ - user environment", "synopsis": "extern char environ;", "tldr_summary": null, "tldr_examples": [], "tldr_source": null, "flags": [], "examples": [], "see_also": [ { "name": "bash", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/bash/1/json" }, { "name": "csh", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/csh/1/json" }, { "name": "env", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/env/1/json" }, { "name": "login", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/login/1/json" }, { "name": "printenv", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/printenv/1/json" }, { "name": "sh", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/sh/1/json" }, { "name": "su", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/su/1/json" }, { "name": "tcsh", "section": "1", "url": "https://www.chedong.com/phpMan.php/man/tcsh/1/json" }, { "name": "execve", "section": "2", "url": "https://www.chedong.com/phpMan.php/man/execve/2/json" }, { "name": "clearenv", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/clearenv/3/json" }, { "name": "exec", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/exec/3/json" }, { "name": "getenv", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/getenv/3/json" }, { "name": "putenv", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/putenv/3/json" }, { "name": "setenv", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/setenv/3/json" }, { "name": "unsetenv", "section": "3", "url": "https://www.chedong.com/phpMan.php/man/unsetenv/3/json" }, { "name": "locale", "section": "7", "url": "https://www.chedong.com/phpMan.php/man/locale/7/json" }, { "name": "ld.so", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/ld.so/8/json" }, { "name": "pamenv", "section": "8", "url": "https://www.chedong.com/phpMan.php/man/pamenv/8/json" } ], "section_outline": [ { "name": "NAME", "lines": 2, "subsections": [] }, { "name": "SYNOPSIS", "lines": 2, "subsections": [] }, { "name": "DESCRIPTION", "lines": 114, "subsections": [] }, { "name": "NOTES", "lines": 12, "subsections": [] }, { "name": "BUGS", "lines": 10, "subsections": [] }, { "name": "SEE ALSO", "lines": 5, "subsections": [] } ], "sections": { "NAME": { "content": "environ - user environment\n", "subsections": [] }, "SYNOPSIS": { "content": "extern char environ;\n", "subsections": [] }, "DESCRIPTION": { "content": "The variable environ points to an array of pointers to strings called the \"environment\". The\nlast pointer in this array has the value NULL. This array of strings is made available to\nthe process by the execve(2) call when a new program is started. When a child process is\ncreated via fork(2), it inherits a copy of its parent's environment.\n\nBy convention, the strings in environ have the form \"name=value\". The name is case-sensitive\nand may not contain the character \"=\". The value can be anything that can be represented as\na string. The name and the value may not contain an embedded null byte ('\\0'), since this is\nassumed to terminate the string.\n\nEnvironment variables may be placed in the shell's environment by the export command in\nsh(1), or by the setenv command if you use csh(1).\n\nThe initial environment of the shell is populated in various ways, such as definitions from\n/etc/environment that are processed by pamenv(8) for all users at login time (on systems\nthat employ pam(8)). In addition, various shell initialization scripts, such as the system-\nwide /etc/profile script and per-user initializations script may include commands that add\nvariables to the shell's environment; see the manual page of your preferred shell for de‐\ntails.\n\nBourne-style shells support the syntax\n\nNAME=value command\n\nto create an environment variable definition only in the scope of the process that executes\ncommand. Multiple variable definitions, separated by white space, may precede command.\n\nArguments may also be placed in the environment at the point of an exec(3). A C program can\nmanipulate its environment using the functions getenv(3), putenv(3), setenv(3), and un‐\nsetenv(3).\n\nWhat follows is a list of environment variables typically seen on a system. This list is in‐\ncomplete and includes only common variables seen by average users in their day-to-day rou‐\ntine. Environment variables specific to a particular program or library function are docu‐\nmented in the ENVIRONMENT section of the appropriate manual page.\n\nUSER The name of the logged-in user (used by some BSD-derived programs). Set at login\ntime, see section NOTES below.\n\nLOGNAME\nThe name of the logged-in user (used by some System-V derived programs). Set at login\ntime, see section NOTES below.\n\nHOME A user's login directory. Set at login time, see section NOTES below.\n\nLANG The name of a locale to use for locale categories when not overridden by LCALL or\nmore specific environment variables such as LCCOLLATE, LCCTYPE, LCMESSAGES, LCMON‐\nETARY, LCNUMERIC, and LCTIME (see locale(7) for further details of the LC* environ‐\nment variables).\n\nPATH The sequence of directory prefixes that sh(1) and many other programs employ when\nsearching for an executable file that is specified as a simple filename (i.a., a path‐\nname that contains no slashes). The prefixes are separated by colons (:). The list\nof prefixes is searched from beginning to end, by checking the pathname formed by con‐\ncatenating a prefix, a slash, and the filename, until a file with execute permission\nis found.\n\nAs a legacy feature, a zero-length prefix (specified as two adjacent colons, or an\ninitial or terminating colon) is interpreted to mean the current working directory.\nHowever, use of this feature is deprecated, and POSIX notes that a conforming applica‐\ntion shall use an explicit pathname (e.g., .) to specify the current working direc‐\ntory.\n\nAnalogously to PATH, one has CDPATH used by some shells to find the target of a change\ndirectory command, MANPATH used by man(1) to find manual pages, and so on.\n\nPWD Absolute path to the current working directory; required to be partially canonical (no\n. or .. components).\n\nSHELL The absolute pathname of the user's login shell. Set at login time, see section NOTES\nbelow.\n\nTERM The terminal type for which output is to be prepared.\n\nPAGER The user's preferred utility to display text files. Any string acceptable as a com‐\nmand-string operand to the sh -c command shall be valid. If PAGER is null or is not\nset, then applications that launch a pager will default to a program such as less(1)\nor more(1).\n\nEDITOR/VISUAL\nThe user's preferred utility to edit text files. Any string acceptable as a com‐\nmandstring operand to the sh -c command shall be valid.\n\nNote that the behavior of many programs and library routines is influenced by the presence or\nvalue of certain environment variables. Examples include the following:\n\n• The variables LANG, LANGUAGE, NLSPATH, LOCPATH, LCALL, LCMESSAGES, and so on influence\nlocale handling; see catopen(3), gettext(3), and locale(7).\n\n• TMPDIR influences the path prefix of names created by tempnam(3) and other routines, and\nthe temporary directory used by sort(1) and other programs.\n\n• LDLIBRARYPATH, LDPRELOAD, and other LD* variables influence the behavior of the dy‐\nnamic loader/linker. See also ld.so(8).\n\n• POSIXLYCORRECT makes certain programs and library routines follow the prescriptions of\nPOSIX.\n\n• The behavior of malloc(3) is influenced by MALLOC* variables.\n\n• The variable HOSTALIASES gives the name of a file containing aliases to be used with geth‐\nostbyname(3).\n\n• TZ and TZDIR give timezone information used by tzset(3) and through that by functions like\nctime(3), localtime(3), mktime(3), strftime(3). See also tzselect(8).\n\n• TERMCAP gives information on how to address a given terminal (or gives the name of a file\ncontaining such information).\n\n• COLUMNS and LINES tell applications about the window size, possibly overriding the actual\nsize.\n\n• PRINTER or LPDEST may specify the desired printer to use. See lpr(1).\n", "subsections": [] }, "NOTES": { "content": "Historically and by standard, environ must be declared in the user program. However, as a\n(nonstandard) programmer convenience, environ is declared in the header file if\nthe GNUSOURCE feature test macro is defined (see featuretestmacros(7)).\n\nThe prctl(2) PRSETMMENVSTART and PRSETMMENVEND operations can be used to control the\nlocation of the process's environment.\n\nThe HOME, LOGNAME, SHELL, and USER variables are set when the user is changed via a session\nmanagement interface, typically by a program such as login(1) from a user database (such as\npasswd(5)). (Switching to the root user using su(1) may result in a mixed environment where\nLOGNAME and USER are retained from old user; see the su(1) manual page.)\n", "subsections": [] }, "BUGS": { "content": "Clearly there is a security risk here. Many a system command has been tricked into mischief\nby a user who specified unusual values for IFS or LDLIBRARYPATH.\n\nThere is also the risk of name space pollution. Programs like make and autoconf allow over‐\nriding of default utility names from the environment with similarly named variables in all\ncaps. Thus one uses CC to select the desired C compiler (and similarly MAKE, AR, AS, FC, LD,\nLEX, RM, YACC, etc.). However, in some traditional uses such an environment variable gives\noptions for the program instead of a pathname. Thus, one has MORE and LESS. Such usage is\nconsidered mistaken, and to be avoided in new programs.\n", "subsections": [] }, "SEE ALSO": { "content": "bash(1), csh(1), env(1), login(1), printenv(1), sh(1), su(1), tcsh(1), execve(2),\nclearenv(3), exec(3), getenv(3), putenv(3), setenv(3), unsetenv(3), locale(7), ld.so(8),\npamenv(8)\n\nLinux man-pages 6.7 2023-10-31 environ(7)", "subsections": [] } } } }