nl:
syntax nl [options] files
number the lines of lines,which are concatenated in the output.but the old files don't
change,it is only change in the terminate.the numbering is done for
each logical page,which is defined as a header,a body,a footer.these
are delimited by the special string \:\:\: , \:\:,
\:,respectively.\:\:\:display the header,\:\:display the body
parameter
-b style
set body numbering style to style,t by default
-f style
set footer number style to style,n by default
-h style
set header numbering style to style.n by default
style can be in these forms
a(A) number all lines
t only number nonempty line(default)
n don't number line
suppose the file1 contains the following text
\:\:\:
header
\:\:
body
\:
footer
illustration:
nl -ba file1 file2;
nl -fa file1;
remember the sequence can't reverse,if do ,will wrong
