SHELL

grep substring in bash

# It can be done in two ways
# 1) Have "grep" read on from the standard input using a pipe
#    and search the input string. Then pipe the result to "wc" to count 
#    the number of occurences

$ line="This is where we select from a table."
# substr="select"

$ echo "$line" | grep "$substr" | wc -l

# 2) or pass a string to "grep" and search the string for a substring
#    pass the result to "wc" to count the number of occurence

$ grep "$substr" <<< "$line" | wc -l

grep substring in shell

# You can do it in two ways
# 1) Let "grep" read on its standard input

echo "$line" | grep -o select

# 2) tell "grep" here is the string

grep select <<< "$line"

grep for substring

output=$(command)
[[ $output =~ (CpuIowait=[0-9][.][0-9]{2}) ]] && echo "${BASH_REMATCH[1]}"