by the way (Unix)

aproposis a command with which the manual files, the so-called manual pages of Unix or Unix-like operating system are searched. This allows you to find a command for a specific task without knowing the name of the command you are looking for.

Delimitation and connection to related commands

apropos is a wrapper for the command man -kand / or implemented as a symbolic link to the command whatis. aproposand whatisare part of the package man-db.

speaking of	what is
Searches both the names and the brief descriptions of the manual pages.	Searches only in the name field of the manual pages.
Finds commands whose names are unknown.	In no more than one sentence, explains the task of commands whose names you know exactly.
Has almost the same functions as the command man -k.	Corresponds to the command man -f.

behavior

With aproposyou can search all manual pages for a keyword or for several keywords. aproposreplies with a list of all manual pages that contain this character string, the search term, in their name or in their short description. When searching for apropos, upper and lower case are always synonymous.

Each apropos response line contains three fields: First the name of the command found and the associated manual page, then as a number in brackets the section of the manual page in which the command was found, and finally the short description from the found manual page.

Application examples

Search in two languages

$ apropos permission rechte
access (2)           - prüft die Zugriffsrechte des Benutzers an einer Datei
chmod (2)            - Zugriffsrechte einer Datei ändern
dh_fixperms (1)      - korrigiert Zugriffsrechte von Dateien in Bauverzeichnissen
faccessat (2)        - prüft die Zugriffsrechte des Benutzers an einer Datei
faked-sysv (1)       - Daemon, der sich an gefälschte Besitz-/Zugriffsrechte von Dateien erinnert, die durch f...
faked-tcp (1)        - Daemon, der sich an gefälschte Besitz-/Zugriffsrechte von Dateien erinnert, die durch f...
fakeroot-sysv (1)    - einen Befehl zur Dateimanipulation in einer Umgebung mit gefälschten Root-Rechten ausf...
fakeroot-tcp (1)     - einen Befehl zur Dateimanipulation in einer Umgebung mit gefälschten Root-Rechten ausf...
fchmod (2)           - Zugriffsrechte einer Datei ändern
fchmodat (2)         - Zugriffsrechte einer Datei ändern
ioperm (2)           - setzt Port-Zugriffsrechte für Eingabe/Ausgabe
kdesu (1)            - Führt ein Programm mit erweiterten Rechten aus.
eaccess (3)          - check effective user's permissions for a file
euidaccess (3)       - check effective user's permissions for a file
faked (1)            - daemon that remembers fake ownership/permissions of files manipulated by fakeroot proces...
WWW::RobotRules (3pm) - database of robots.txt-derived permissions
XF86VidModeGetPermissions (3) - Extension library for the XFree86-VidMode X extension

This example searches aproposfor all manual pages with one of the words “permission” or “rights” in their name or brief description. Since it is apropos case-insensitive , manual pages are also found with a short description containing the noun “rights”.

Search with regular expressions

$ apropos abc.n Xzl xzless (1) - view (text) files compressed with xz or lzma
XTestGr abCon trol (3) - XTest extension functions

As you can see again, aproposhis search does not distinguish between upper and lower case; although Xzl was specified as to be searched for, xzless was found. In addition, aproposthe search terms are understood by default as regular expressions (also called “regex” for short). The regular expression " abc.n", which was used in the example, stands for all character strings which, regardless of upper and lower case, contain the characters ABC, then any character and after this an N, and because this search pattern ("pattern") matches the string " abCon" is XTestGrabControlfound.

Search without regular expressions

TkMan explains how to access the function of apropos.

$ apropos --exact abc.n xzl abc.n : nothing suitable.
xzl : nothing suitable.

With the " --exact" option , the first thing is abc.nno longer a regular expression, the point is no longer a placeholder for any character, but simply a point. Second, when using this option, the keyword or search pattern transferred must include the complete command name or the complete Include brief description. This second is why the previous example xzldoes not find xzless.

$ apropos --exact xzless xzless (1) - view (text) files compressed with xz or lzma

Graphic user interfaces

The TkMan program has integrated queries with apropos into its user interface .

Web links

Wiktionary: apropos  - explanations of meanings, word origins, synonyms, translations

• apropos(1) -  OpenBSD General Commands Manual
• apropos(1) -  FreeBSD General Commands Manual