grep on a variable

Let’s say I have a variable

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

now I want to grep how many times does select occur in the sentence.

grep -ci "select" $line

I tried that, but it did not work. I also tried

grep -ci "select" "$line"

It still doesn’t work. I get the following error.

grep: This is where we select from a table.: No such file or directory

Answers:

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Method 1

Have grep read on its standard input. There you go, using a pipe…

$ echo "$line" | grep select

… or a here string…

$ grep select <<< "$line"

Also, you might want to replace spaces by newlines before grepping :

$ echo "$line" | tr ' ' 'n' | grep select

… or you could ask grep to print the match only:

$ echo "$line" | grep -o select

This will allow you to get rid of the rest of the line when there’s a match.

Edit: Oops, read a little too fast, thanks Marco. In order to count the occurences, just pipe any of these to wc(1) 😉

Another edit made after lzkata‘s comment, quoting $line when using echo.

Method 2

test=$line i=0
while case "$test" in (*select*)
test=${test#*select};;(*) ! :;;
esac; do i=$(($i+1)); done

You don’t need to call grep for such a simple thing.

Or as a function:

occur() while case "$1" in (*"$2"*) set -- 
        "${1#*"$2"}" "$2" "${3:-0}" "$((${4:-0}+1))";;
        (*) return "$((${4:-0}<${3:-1}))";;esac
        do : "${_occur:+$((_occur=$4))}";done

It takes 2 or 3 args. Providing any more than that will skew its results. You can use it like:

_occur=0; occur ... . 2 && echo "count: $_occur"

…which prints the occurrence count of . in ... if it occurs at least 2 times. Like this:

count: 3

If $_occur is either empty or unset when it is invoked then it will affect no shell variables at all and return 1 if "$2" occurs in "$1" fewer than "$3" times. Or, if called with only two args, it will return 1 only if "$2" is not in "$1". Else it returns 0.

And so, in its simplest form, you can do:

occur '' . && echo yay || echo shite

…which prints…

shite

…but…

occur . . && echo yay || echo shite

…will print…

yay

You might also write it a little differently and omit the quotes around $2 in both the (*"$2"*) and "${1#*"$2"}" statement. If you do that then you can use shell globs for matches like sh[io]te for the match test.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0