how to view previous version of a file in Mercurial

Question

I am using mercurial for version control of a few files in a directory. Suppose I have 10 commits (10 changesets or revisions). I want to just view how a particular file, say th

Answer 1

hg cat [OPTION]... FILE...

Print the specified files as they were at the given revision. 
If no revision is given, the parent of the working directory is used, 
or tip if no revision is checked out.

Output may be to a file, in which case the name of the file is given 
using a format string. The formatting rules are the same as for the 
export command, with the following additions:
%s: basename of file being printed
%d: dirname of file being printed, or '.' if in repository root
%p: root-relative path name of file being printed

Returns 0 on success.

options:
-o, --output    print output to file with formatted name
-r, --rev   print the given revision
--decode    apply any matching decode filter
-I, --include   include names matching the given patterns
-X, --exclude   exclude names matching the given patterns