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This article is about how Bash extracts substrings. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

The so-called "substring" is a string that appears in other strings. For example, "3382" is a substring of "this is a 3382 test". There are several ways to extract a number or a specified part of a string.

Extract substrings in Bash

Its syntax is:

# # format # # ${parameter:offset:length}

Substring extension is a feature of bash. It expands to a string in the parameter value that starts with offset and is length characters long. Suppose that $u is defined as follows:

# # define variable u # # u = "this is a test"

Then the substring extension of the following parameters extracts the substring:

Var= "${uvl 10 var 4}" echo "${var}"

The result is:

Test

These parameters represent:

10: offset position 4: length

Use IFS

According to the man page description of bash:

IFS (internal field delimiter) is used to split words after expansion and to split lines into words with the built-in read command. The default value is.

Another POSIX-ready POSIX ready scenario is as follows:

U = "this is a test" set-- $uecho "$1" echo "$2" echo "$3" echo "$4"

The output is:

Thisisatest

The following is a piece of bash code that removes the url with a home page from Cloudflare cache.

#! / bin/bash### Author-Vivek Gite {https://www.cyberciti.biz/}## Purpose-Purge CF cache## License-Under GPL ver 3.x+## # set me first # # zone_id= "YOUR_ZONE_ID_HERE" api_key= "YOUR_API_KEY_HERE" email_id= "YOUR_EMAIL_ID_HERE" # # hold data # # home_url= "amp_url="urls=" $@ "# Show usage [" $urls "="] & & {echo" Usage: $0 url1 url2 url3 " Exit 1;} # Get home page url as we have various sub dirs on domain## / tips/## / faq/get_home_url () {local u = "$1" IFS='/'set-- $uecho "${1} ${IFS} ${IFS} ${3} ${IFS} ${4} ${IFS}"} echoecho "Purging cache from Cloudflare. ... " Echofor u in $urlsdohome_url= "$(get_home_url $u)" amp_url= "${u} amp/" curl-X DELETE "https://api.cloudflare.com/client/v4/zones/${zone_id}/purge_cache"\-H" X-Auth-Email: ${email_id} "\-H" X-Auth-Key: ${api_key} "\-H" Content-Type: application/json "--data" {\ "files\": [\ "${u}\" \ "${amp_url}\",\ "${home_url}\"]} "echodoneecho

It can be used as follows:

~ / bin/cf.clear.cache https://www.cyberciti.biz/faq/bash-for-loop/https://www.cyberciti.biz/tips/linux-security.html with the help of cut command

You can use the cut command to delete each line or part of a variable in the file. Its syntax is:

U = "this is a test" echo "$u" | cut-d''- f 4echo "$u" | cut-- delimiter=''--fields=4#### WHERE##-d'': Use a whitespace as delimiter##-f 4: Select only 4th field# # # var= "$(cut-d'- f 4" echo "${var}"

To learn more, read bash's man page:

Man bashman cut

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