Add thousands separator in a number

bash's printf supports pretty much everything you can do in the printf C function

type printf           # => printf is a shell builtin
printf "%'d" 123456   # => 123,456

printf from coreutils will do the same

/usr/bin/printf "%'d" 1234567   # => 1,234,567

With sed:

$ echo "123456789" | sed 's/\([[:digit:]]\{3\}\)\([[:digit:]]\{3\}\)\([[:digit:]]\{3\}\)/\1,\2,\3/g'
123,456,789

(Note that this only works for exactly 9 digits!)

or this with sed:

$ echo "123456789" | sed ':a;s/\B[0-9]\{3\}\>/,&/;ta'
123,456,789

With printf:

$ LC_NUMERIC=en_US printf "%'.f\n" 123456789
123,456,789

You can use numfmt:

$ numfmt --grouping 123456789
123,456,789

Or:

$ numfmt --g 123456789
123,456,789

Note that numfmt is not a POSIX utility, it is part of GNU coreutils.

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