grep on a variable

Question

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

Solution 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.

Solution 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.

Comments

[Marek Zakrzewski]

You need to use herestring ...<<<"$line" . The command grep is expecting a file instead

[Ciro Santilli Путлер Капут 六四事]

stackoverflow.com/questions/2106526/…

[Marco]

Since the OP wants to count the number of occurrences of a string you can add a wc to complete the task: grep -o <string> <<< "$variable" | wc -l

[yorkshiredev]

+1: Faster, indeed. Works in bash and dash/sh (and probably a few others).

[Izkata]

Use echo "$line" to preserve existing newlines instead of creating ones with tr

[mikeserv]

@JohnWHSmith - the edit is better, but still just as portable.

[Michael A]

What is the availability of a Here String? Does it require Bash or another shell?

[Aubergine]

i don't understand how bash question indexing is so bad, answers do not answer the question, how to do: myoutput | grep -v $SOMEVAR condition itself is a variable.

[Amit Naidu]

@Aubergine: copy-pastable examples - Filter-string is a variable: seq 4 | grep -v $SHLVL ; Filter-string from a different process: seq 4 | grep -v "$(seq 2)" Or seq 4 | grep -vf <(seq 2) ; Input from a different process: grep -v $SHLVL <(seq 4) Or grep -v $SHLVL <<< "$(seq 4)"

[Admin]

This looks a lot like John WH Smith’s answer. OK, you’ve added grep -w, but you haven’t explained what that does.

[Admin]

The difference between my answer an Mr. Smith's is that the OP asked for how many matches in a sentence/string, and, to the best of my knowledge, the method using grep (as the OP requested) does not break the sentence into individual lines so that grep can go through it (which is why I used sed). Then wc -l was added to count the number of lines after the regex "select" was matched. The -w on grep makes it only match whole-word results, so something like "selection" won't trigger the filter

[Admin]

Sorry, upon re-reading, I didn't see the 'tr' command with grep initially. So the only difference in my answer and Mr. Smith's is the use of sed

[Admin]

There's too many 'e's in argument (twice)

[Admin]

Fixed, thanks Greenonline!