{"id":5371,"date":"2018-07-12T20:04:14","date_gmt":"2018-07-12T16:04:14","guid":{"rendered":"https:\/\/www.howtoforge.com\/linux-apropos-command\/"},"modified":"2018-07-12T20:04:14","modified_gmt":"2018-07-12T16:04:14","slug":"linux-apropos-command-tutorial-for-beginners-5-examples","status":"publish","type":"post","link":"https:\/\/afaghhosting.net\/blog\/linux-apropos-command-tutorial-for-beginners-5-examples\/","title":{"rendered":"Linux apropos Command Tutorial for Beginners (5 Examples)"},"content":{"rendered":"

In Linux, if you ever need help regarding a command, all you need to do is to open its man page. But what if a situation arises wherein the requirement is\u00a0to quickly search the names and descriptions of all available man pages? Well, Linux has got your covered, as there exists a command dubbed apropos<\/strong> that does exactly this for you.<\/p>\n

In this tutorial, we will discuss the basics of apropos using some easy to understand examples. But before we do that, it’s worth mentioning that all examples here have been tested on an Ubuntu 16.04 LTS machine.<\/p>\n

The apropos command searches manual page names and descriptions for a user-supplied keyword. Following is its syntax:<\/p>\n

apropos [OPTIONS] keyword …<\/p>\n

And here’s what the tool’s man page says about it:<\/p>\n

 Each manual page has a short description available within it.\u00a0\u00a0 apropos\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 searches the descriptions for instances of keyword.
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 keyword\u00a0 is\u00a0 usually\u00a0 a regular expression, as if (-r) was used, or may\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 contain wildcards (-w), or match the exact keyword (-e).\u00a0\u00a0 Using\u00a0 these\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 options,\u00a0 it\u00a0 may\u00a0 be\u00a0 necessary to quote the keyword or escape (\\) the\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 special characters to stop the shell from interpreting them.<\/p>
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 The standard matching rules allow matches to be made against\u00a0 the\u00a0 page\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 name and word boundaries in the description.<\/p>
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 The\u00a0 database\u00a0 searched\u00a0 by\u00a0 apropos\u00a0 is\u00a0 updated by the mandb program.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Depending on your installation, this may be run by a periodic cron job,\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 or\u00a0 may\u00a0 need\u00a0 to\u00a0 be\u00a0 run\u00a0 manually\u00a0 after\u00a0 new manual pages have been\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 installed.<\/p><\/pre>\n
Following are some Q&A-styled examples that should give you a good idea on how the apropos command works.<\/p>\n
Q1. How to use apropos?<\/h2>\n
Basic usage is simple. Just pass the keyword you want to search as input to the apropos command.<\/p>\n
For example:<\/p>\n
apropos dmesg<\/p>\n
produced the following result:<\/p>\n
dmesg (1)\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 - print or control the kernel ring buffer<\/pre>\n
Of course, you can pass multiple keywords as well.<\/p>\n
For example:<\/p>\n
apropos dmesg whereis<\/p>\n
Following is the output in this case:<\/p>\n
dmesg (1)\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 - print or control the kernel ring bufferwhereis (1)\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 - locate the binary, source, and manual page files for a...<\/pre>\n
Q2. How to make apropos search for exact keywords?<\/h2>\n
By default, the input you pass to the apropos command isn’t searched exactly. For example, if you pass ‘who’ as an input, you’ll also see the tool producing results containing words like ‘whoami’.<\/p>\n
\"How<\/a><\/p>\n
So this isn’t an exact search. However, you can force apropos to search for exact keywords by using the -e or –exact command line options.<\/p>\n
\"apropos<\/a><\/p>\n
So now you see that only those entries that exactly match ‘who’ were displayed in the output.<\/p>\n
Q3. How to make apropos display entries matching all keywords?<\/h2>\n
If you pass multiple keywords as input to the apropos command, the tool will output entries that match\/contain at least one of the keywords. However, if you want apropos to produce only those entries that match\/contain all keywords, then use the -a command line option.<\/p>\n
For example, here’s the output of an apropos command without the -a option:<\/p>\n
\"How<\/a><\/p>\n
And here’s the output with -a option enabled:<\/p>\n
\"apropos<\/a><\/p>\n
Q4. How to force apropos to not trim output?<\/h2>\n
As you’d have seen in output in previous Q&As, the tool trims entries if they are too long. For example, see the highlighted line in the following output:<\/p>\n
\"How<\/a><\/p>\n
However, if you want, you can force apropos to produce complete lines in output, something which you can do using the -l command line option.<\/p>\n
\"force<\/a><\/p>\n
Q5. How to interpret apropos exit status?<\/h2>\n
The apropos command produces four different exit status: 0, 1, 2, and 16. Here’s what each of these represents:<\/p>\n
 0\u00a0\u00a0\u00a0\u00a0\u00a0 Successful program execution.
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 1\u00a0\u00a0\u00a0\u00a0\u00a0 Usage, syntax or configuration file error.<\/p>
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 2\u00a0\u00a0\u00a0\u00a0\u00a0 Operational error.<\/p>
\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 16\u00a0\u00a0\u00a0\u00a0 Nothing was found that matched the criteria specified<\/p><\/pre>\n
Conclusion<\/h2>\n
Depending on your work profile, you might not require the apropos command on daily basis, but as you’d have understood by now, it could be a lifesaver in certain situations. We’ve discussed some use command line options here. To know more about the tool, head to its man page<\/a>.<\/p>\n
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In Linux, if you ever need help regarding a command, all you need to do is to open its man page. But what if a situation arises wherein the requirement is\u00a0to quickly search the names and descriptions of all available man pages? Well, Linux has got your covered, as there exists a command dubbed apropos …<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[36],"tags":[],"class_list":["post-5371","post","type-post","status-publish","format-standard","hentry","category-36"],"_links":{"self":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts\/5371","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/comments?post=5371"}],"version-history":[{"count":0,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/posts\/5371\/revisions"}],"wp:attachment":[{"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/media?parent=5371"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/categories?post=5371"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/afaghhosting.net\/blog\/wp-json\/wp\/v2\/tags?post=5371"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}