How to count the number of specific characters in a file in Linux

Counting the number of a string in a file is actually like looking for stones in a piece of sand. Some people make a mark on the stone after seeing it (grep), and then remember how many marks they made; some people dig it up after seeing the stone (tr), and finally count how many stones they dug; some people jump over the stone after seeing it (awk), and then count how many times they jumped.

This is the file I used

[root@bzhou test]# cat file
hafsdha
hahafsdfsdhaha
haha

I want to match the string 'haha'

1. Grep's -o option

[root@bzhou test]# grep -c 'haha' file
2

At the beginning, the -c option was used, but -c can only count one line. If there are multiple matching strings in a line, -c will be powerless.

This is correct

[root@bzhou test]# grep -o 'haha' file | wc -l
3

2. awk

This thing is thanks to blackold on CU.

[root@bzhou test]# awk -v RS='haha' 'END {print --NR}' file

-v is used to set the value of a variable. RS is the record separator. The default is new line (\n), which means that awk reads data line by line. But now when RS is 'haha', it reads data as 'haha'. NR is the number of records read. n records are separated by n-1 separators, so it is --NR.

3.tr

Strictly speaking, tr cannot match strings, it can only match single characters. Here we match the number of 'h' in this file.

[root@bzhou test]# tr -cd 'h' <file | wc -c
8
[root@bzhou test]# grep -o 'h' file | wc -l
8

-d can delete a certain character. If only -d is used, the string after deleting the specific character will be output. However, -c can reverse the display, which means that the deleted characters are displayed. Then you can use wc -c to count the number of characters.

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