[bash] How can I count the occurrences of a string within a file?

Just take this code as an example. Pretending it is an HTML/text file, if I would like to know the total number of times that echo appears, how can I do it using bash?

new_user()
{
    echo "Preparing to add a new user..."
    sleep 2
    adduser     # run the adduser program
}

echo "1. Add user"
echo "2. Exit"

echo "Enter your choice: "
read choice


case $choice in
    1) new_user     # call the new_user() function
       ;;
    *) exit
       ;;
esac 

if you just want the number of occurences then you can do this, $ grep -c "string_to_count" file_name

The number of string occurrences (not lines) can be obtained using grep with -o option and wc (word count):

$ echo "echo 1234 echo" | grep -o echo
echo
echo
$ echo "echo 1234 echo" | grep -o echo | wc -l
2

So the full solution for your problem would look like this:

$ grep -o "echo" FILE | wc -l

I'm taking some guesses here, because I don't quite understand what you're asking.

I think that what you want is a count of the number of lines on which the pattern 'echo' appears in the given file.

I've pasted your sample text into a file called 6741967.

First, grep finds the matches:

james@Brindle:tmp$grep echo 6741967 
    echo "Preparing to add a new user..."
echo "1. Add user"
echo "2. Exit"
echo "Enter your choice: "

Second, use wc -l to count the lines

james@Brindle:tmp$grep echo 6741967  | wc -l
       4

None of the existing answers worked for me with a single-line 10GB file. Grep runs out of memory even on a machine with 768 GB of RAM!

$ cat /proc/meminfo | grep MemTotal
MemTotal:       791236260 kB
$ ls -lh test.json
-rw-r--r-- 1 me all 9.2G Nov 18 15:54 test.json
$ grep -o '0,0,0,0,0,0,0,0,' test.json  | wc -l
grep: memory exhausted
0

So I wrote a very simple Rust program to do it.

1. Install Rust.
2. cargo install count_occurences

$ count_occurences '0,0,0,0,0,0,0,0,' test.json
99094198

It's a little slow (1 minute for 10GB), but at least it doesn't run out of memory!