mjhjmtu

I'm trying to learn command line better and wondering what the difference between these two commands would be.

grep -c ^b example 

and

grep ^b example| cat –n

Well, according to the manual, grep:

searches for PATTERN in each FILE. By
default, grep prints the matching lines.

and with the -c flag:

-c, --count

Suppress normal output; instead print a count of matching
lines for each input file.

So, grep -c ^b example prints the number (count) of lines matching the pattern, while grep ^b example prints the lines themselves.

As for cat, it's described to

concatenate files and print on the standard output

and what the -n flag does is to:

-n, --number 

number all output lines

Given the pipe and no file names, cat reads from the pipe, so the output is the output of grep, with line numbers added. Hence grep ^b example| cat –n prints all matching lines, numbered.

This is different from grep -n ^b example, where grep adds the line numbers of the matches. grep knows the line numbers of the original file, while cat only sees the output of grep and numbers the lines accordingly.

So, given the input file

$ cat example 
bar
foo
basf

We have:

$ grep -c ^b example 
2

$ grep ^b example |cat -n
 1 bar
 2 basf

$ grep -n ^b example
1:bar
3:basf

Ok command:

1. grep -c ^b example: Output the count for matching lines for lines that begin with letter b, and




2. grep ^b example | cat -n: pass the result of the grep command to the cat command and list them with line numbers. The -n forces cat to list them along with lines numbers.

Example:

example.txt with content:

media sound3
media sound1
media sound2
find sound -type f -name sound[0-9] -printf 'media %fn' > file.txt
find sound -type f -name sound[0-9] -exec bash -c 'echo media bash >> file.txt' ;
find sound -type f -name sound[0-9] -exec bash -c "f=''; echo media $( basename $f) >> file.txt" ;

Result from (1):

3

Result from (2):

1 media sound3
2 media sound1
3 media sound2