When "grep -c" doesn't cut it (counts only 1 occurrence per line).

perl -lne '$c++ while /SEARCH_STRING/g; END { print $c; }'

For example, to count the number of times ABCD appears in mysqldump output:

mysqldump my_db | perl -lne '$c++ while /ABCD/g; END { print $c; }'

Modified version of snippet found in http://www.wellho.net/forum/Perl-Programming/Issue-with-Grep.html

From one of the comments in http://www.vim.org/tips/tip.php?tip_id=689

:%s/word/&/g

The above substitutes "word" for itself, and tells you the number of substitutions made.

Bundle my_dir

tar cvf - my_dir | gzip -c > my_dir.tar.gz

Unbundle my_dir

gunzip -c my_dir.tar.gz | tar xvf -