sed나 awk 대신에 parameter substitution 를 이용하자

string="TestT100String"

echo ${string//[^[:digit:]]/}

결과

 

 

 

 

Summary: String Manipulation and Expanding Variables

For your ready references here are all your handy bash parameter substitution operators. Try them all; enhance your scripting skills like a pro:

${parameter:-defaultValue}	Get default shell variables value
${parameter:=defaultValue}	Set default shell variables value
${parameter:?"Error Message"}	Display an error message if parameter is not set
${#var}	Find the length of the string
${var%pattern}	Remove from shortest rear (end) pattern
${var%%pattern}	Remove from longest rear (end) pattern
${var:num1:num2}	Substring
${var#pattern}	Remove from shortest front pattern
${var##pattern}	Remove from longest front pattern
${var/pattern/string}	Find and replace (only replace first occurrence)
${var//pattern/string}	Find and replace all occurrences
${!prefix*}	Expands to the names of variables whose names begin with prefix.
${var,} ${var,pattern}	Convert first character to lowercase.
${var,,} ${var,,pattern}	Convert all characters to lowercase.
${var^} ${var^pattern}	Convert first character to uppercase.
${var^^} ${var^^pattern}	Convert all character to uppercase..

 

https://www.cyberciti.biz/tips/bash-shell-parameter-substitution-2.html

How To Use Bash Parameter Substitution Like A Pro

 

추가로 하나더! 이건 뭐지?

Bash, Dash, KornShell (ksh), Z shell (zsh) 에서 다음 처럼 테스트 할 수 있다.

test "${string#*$word}" != "$string" && echo "$word found in $string"

테스트 명령어?