How to count number of lines in a text file using Linux shell

Sometimes you need an easy way to count number of lines in a text file.
For example, how many lines in a .csv file.

Easy:

wc -l somefilename.csv

You can also count number of characters in a file using "wc":

wc -m somefilename.txt

Or number of words:

wc -w somefilename.txt

Explore the possiblities of "wc":

# wc --help
Usage: wc [OPTION]... [FILE]...
Print newline, word, and byte counts for each FILE, and a total line if
more than one FILE is specified.  With no FILE, or when FILE is -,
read standard input.
  -c, --bytes            print the byte counts
  -m, --chars            print the character counts
  -l, --lines            print the newline counts
  -L, --max-line-length  print the length of the longest line
  -w, --words            print the word counts
      --help     display this help and exit
      --version  output version information and exit

Report bugs to <bug-coreutils@gnu.org>.