Linux apropos is a very handy command used to search all manual pages and descriptions. It will help to search for exact keyword on all manual pages, or find matching keywords. Below are few of the apropos commands and examples with output.
apropos - search the manual page names and descriptions
apropos [-dalv?V] [-e|-w|-r] [-s list] [-m system[,...]] [-M path] [-L locale] [-C file] key‐word ...
Each manual page has a short description available within it. apropos searches the descrip‐ tions for instances of keyword. keyword is usually a regular expression, as if (-r) was used, or may contain wildcards (-w), or match the exact keyword (-e). Using these options, it may be necessary to quote the key‐ word or escape (\) the special characters to stop the shell from interpreting them. The standard matching rules allow matches to be made against the page name and word bound‐ aries in the description. The database searched by apropos is updated by the mandb program. Depending on your instal‐ lation, this may be run by a periodic cron job, or may need to be run manually after new man‐ ual pages have been installed.
OPTIONS -d, --debug Print debugging information. -v, --verbose Print verbose warning messages. -r, --regex Interpret each keyword as a regular expression. This is the default behaviour. Each keyword will be matched against the page names and the descriptions independently. It can match any part of either. The match is not limited to word boundaries. -w, --wildcard Interpret each keyword as a pattern containing shell style wildcards. Each keyword will be matched against the page names and the descriptions independently. If --exact is also used, a match will only be found if an expanded keyword matches an entire de‐ scription or page name. Otherwise the keyword is also allowed to match on word bound‐ aries in the description. -e, --exact Each keyword will be exactly matched against the page names and the descriptions. -a, --and Only display items that match all the supplied keywords. The default is to display items that match any keyword. -l, --long Do not trim output to the terminal width. Normally, output will be truncated to the terminal width to avoid ugly results from poorly-written NAME sections. -s list, --sections=list, --section=list Search only the given manual sections. list is a colon- or comma-separated list of sections. If an entry in list is a simple section, for example "3", then the dis‐ played list of descriptions will include pages in sections "3", "3perl", "3x", and so on; while if an entry in list has an extension, for example "3perl", then the list will only include pages in that exact part of the manual section. -m system[,...], --systems=system[,...] If this system has access to other operating system's manual page descriptions, they can be searched using this option. To search NewOS's manual page descriptions, use the option -m NewOS. The system specified can be a combination of comma-delimited operating system names. To include a search of the native operating system's whatis descriptions, include the system name man in the argument string. This option will override the $SYSTEM envi‐ ronment variable. -M path, --manpath=path Specify an alternate set of colon-delimited manual page hierarchies to search. By de‐ fault, apropos uses the $MANPATH environment variable, unless it is empty or unset, in which case it will determine an appropriate manpath based on your $PATH environment variable. This option overrides the contents of $MANPATH. -L locale, --locale=locale apropos will normally determine your current locale by a call to the C function setlo‐ cale(3) which interrogates various environment variables, possibly including $LC_MES‐ SAGES and $LANG. To temporarily override the determined value, use this option to supply a locale string directly to apropos. Note that it will not take effect until the search for pages actually begins. Output such as the help message will always be displayed in the initially determined locale. -C file, --config-file=file Use this user configuration file rather than the default of ~/.manpath. -?, --help Print a help message and exit. --usage Print a short usage message and exit. -V, --version Display version information.
/*Below command will print verbose warning messages for command head*/ apropos -v head /*Below command will allow to pass wildcard entries*/ apropos -w head* /*Below command will look for exact matching keyword*/ apropos -e head /*Below command will NOT trim the description of the man page descriptions*/ apropos -wl ls*
apropos head will search all the manual pages and list the descriptions of matching keyword
root@letusstudy:~# apropos head HEAD (1p) - Simple command line user agent arm2hpdl (1) - Add HP download header/trailer to an ARM ELF binary. CIRCLEQ_HEAD (3) - implementations of singly-linked lists, singly-linked tail queues, lists and ... CIRCLEQ_INSERT_HEAD (3) - implementations of singly-linked lists, singly-linked tail queues, lists a... elfedit (1) - update ELF header and program property of ELF files git-pack-refs (1) - Pack heads and tags for efficient repository access git-reset (1) - Reset current HEAD to the specified state h2ph (1) - convert .h C header files to .ph Perl header files h2xs (1) - convert .h C header files to Perl extensions head (1) - output the first part of files head (1posix) - copy the first part of files root@letusstudy:~#
apropos --exact head will search all the manual pages and list the descriptions of exact matching keyword
root@letusstudy:~# apropos --exact head HEAD (1p) - Simple command line user agent git-reset (1) - Reset current HEAD to the specified state head (1) - output the first part of files head (1posix) - copy the first part of files root@letusstudy:~#
0 - Successful program execution.
1 - Usage, syntax or configuration file error.
2 - Operational error.
16 - Nothing was found that matched the criteria specified.
SYSTEM If $SYSTEM is set, it will have the same effect as if it had been specified as the ar‐ gument to the -m option.
MANPATH If $MANPATH is set, its value is interpreted as the colon-delimited manual page hier‐ archy search path to use.
MANWIDTH If $MANWIDTH is set, its value is used as the terminal width (see the --long option). If it is not set, the terminal width will be calculated using the value of $COLUMNS, and ioctl(2) if available, or falling back to 80 characters if all else fails.
POSIXLY_CORRECT If $POSIXLY_CORRECT is set, even to a null value, the default apropos search will be as an extended regex (-r). Nowadays, this is the default behaviour anyway.
An FHS compliant global index database cache.
A traditional whatis text database.
SEE ALSO man(1), whatis(1), mandb(8)