How to extract substrings from Bash
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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