Using sed

# FILE SPACING:

 # double space a file
 sed G

 # double space a file which already has blank lines in it. Output file
 # should contain no more than one blank line between lines of text.
 sed '/^$/d;G'

 # triple space a file
 sed 'G;G'

 # undo double-spacing (assumes even-numbered lines are always blank)
 sed 'n;d'

 # insert a blank line above every line which matches "regex"
 sed '/regex/{x;p;x;}'

 # insert a blank line below every line which matches "regex"
 sed '/regex/G'

 # insert a blank line above and below every line which matches "regex"
 sed '/regex/{x;p;x;G;}'

# NUMBERING:

 # number each line of a file (simple left alignment). Using a tab (see
 # note on 't' at end of file) instead of space will preserve margins.
 sed = filename | sed 'N;s/n/t/'

 # number each line of a file (number on left, right-aligned)
 sed = filename | sed 'N; s/^/     /; s/ *(.{6,})n/1  /'

 # number each line of file, but only print numbers if line is not blank
 sed '/./=' filename | sed '/./N; s/n/ /'

 # count lines (emulates "wc -l")
 sed -n '$='

# TEXT CONVERSION AND SUBSTITUTION:

 # IN UNIX ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format.
 sed 's/.$//'               # assumes that all lines end with CR/LF
 sed 's/^M$//'              # in bash/tcsh, press Ctrl-V then Ctrl-M
 sed 's/x0D$//'            # works on ssed, gsed 3.02.80 or higher

 # IN UNIX ENVIRONMENT: convert Unix newlines (LF) to DOS format.
 sed "s/$/`echo -e r`/"            # command line under ksh
 sed 's/$'"/`echo r`/"             # command line under bash
 sed "s/$/`echo r`/"               # command line under zsh
 sed 's/$/r/'                        # gsed 3.02.80 or higher

 # IN DOS ENVIRONMENT: convert Unix newlines (LF) to DOS format.
 sed "s/$//"                          # method 1
 sed -n p                             # method 2

 # IN DOS ENVIRONMENT: convert DOS newlines (CR/LF) to Unix format.
 # Can only be done with UnxUtils sed, version 4.0.7 or higher. The
 # UnxUtils version can be identified by the custom "--text" switch
 # which appears when you use the "--help" switch. Otherwise, changing
 # DOS newlines to Unix newlines cannot be done with sed in a DOS
 # environment. Use "tr" instead.
 sed "s/r//" infile >outfile         # UnxUtils sed v4.0.7 or higher
 tr -d r <infile >outfile            # GNU tr version 1.22 or higher

 # delete leading whitespace (spaces, tabs) from front of each line
 # aligns all text flush left
 sed 's/^[ t]*//'                    # see note on 't' at end of file

 # delete trailing whitespace (spaces, tabs) from end of each line
 sed 's/[ t]*$//'                    # see note on 't' at end of file

 # delete BOTH leading and trailing whitespace from each line
 sed 's/^[ t]*//;s/[ t]*$//'

 # insert 5 blank spaces at beginning of each line (make page offset)
 sed 's/^/     /'

 # align all text flush right on a 79-column width
 sed -e :a -e 's/^.{1,78}$/ &/;ta'  # set at 78 plus 1 space

 # center all text in the middle of 79-column width. In method 1,
 # spaces at the beginning of the line are significant, and trailing
 # spaces are appended at the end of the line. In method 2, spaces at
 # the beginning of the line are discarded in centering the line, and
 # no trailing spaces appear at the end of lines.
 sed  -e :a -e 's/^.{1,77}$/ & /;ta'                     # method 1
 sed  -e :a -e 's/^.{1,77}$/ &/;ta' -e 's/( *)1/1/'  # method 2

 # substitute (find and replace) "foo" with "bar" on each line
 sed 's/foo/bar/'             # replaces only 1st instance in a line
 sed 's/foo/bar/4'            # replaces only 4th instance in a line
 sed 's/foo/bar/g'            # replaces ALL instances in a line
 sed 's/(.*)foo(.*foo)/1bar2/' # replace the next-to-last case
 sed 's/(.*)foo/1bar/'            # replace only the last case

 # substitute "foo" with "bar" ONLY for lines which contain "baz"
 sed '/baz/s/foo/bar/g'

 # substitute "foo" with "bar" EXCEPT for lines which contain "baz"
 sed '/baz/!s/foo/bar/g'

 # change "scarlet" or "ruby" or "puce" to "red"
 sed 's/scarlet/red/g;s/ruby/red/g;s/puce/red/g'   # most seds
 gsed 's/scarlet|ruby|puce/red/g'                # GNU sed only

 # reverse order of lines (emulates "tac")
 # bug/feature in HHsed v1.5 causes blank lines to be deleted
 sed '1!G;h;$!d'               # method 1
 sed -n '1!G;h;$p'             # method 2

 # reverse each character on the line (emulates "rev")
 sed '/n/!G;s/(.)(.*n)/&21/;//D;s/.//'

 # join pairs of lines side-by-side (like "paste")
 sed '$!N;s/n/ /'

 # if a line ends with a backslash, append the next line to it
 sed -e :a -e '/$/N; s/n//; ta'

 # if a line begins with an equal sign, append it to the previous line
 # and replace the "=" with a single space
 sed -e :a -e '$!N;s/n=/ /;ta' -e 'P;D'

 # add commas to numeric strings, changing "1234567" to "1,234,567"
 gsed ':a;s/B[0-9]{3}>/,&/;ta'                     # GNU sed
 sed -e :a -e 's/(.*[0-9])([0-9]{3})/1,2/;ta'  # other seds

 # add commas to numbers with decimal points and minus signs (GNU sed)
 gsed -r ':a;s/(^|[^0-9.])([0-9]+)([0-9]{3})/12,3/g;ta'

 # add a blank line every 5 lines (after lines 5, 10, 15, 20, etc.)
 gsed '0~5G'                  # GNU sed only
 sed 'n;n;n;n;G;'             # other seds

# SELECTIVE PRINTING OF CERTAIN LINES:

 # print first 10 lines of file (emulates behavior of "head")
 sed 10q

 # print first line of file (emulates "head -1")
 sed q

 # print the last 10 lines of a file (emulates "tail")
 sed -e :a -e '$q;N;11,$D;ba'

 # print the last 2 lines of a file (emulates "tail -2")
 sed '$!N;$!D'

 # print the last line of a file (emulates "tail -1")
 sed '$!d'                    # method 1
 sed -n '$p'                  # method 2

 # print the next-to-the-last line of a file
 sed -e '$!{h;d;}' -e x              # for 1-line files, print blank line
 sed -e '1{$q;}' -e '$!{h;d;}' -e x  # for 1-line files, print the line
 sed -e '1{$d;}' -e '$!{h;d;}' -e x  # for 1-line files, print nothing

 # print only lines which match regular expression (emulates "grep")
 sed -n '/regexp/p'           # method 1
 sed '/regexp/!d'             # method 2

 # print only lines which do NOT match regexp (emulates "grep -v")
 sed -n '/regexp/!p'          # method 1, corresponds to above
 sed '/regexp/d'              # method 2, simpler syntax

 # print the line immediately before a regexp, but not the line
 # containing the regexp
 sed -n '/regexp/{g;1!p;};h'

 # print the line immediately after a regexp, but not the line
 # containing the regexp
 sed -n '/regexp/{n;p;}'

 # print 1 line of context before and after regexp, with line number
 # indicating where the regexp occurred (similar to "grep -A1 -B1")
 sed -n -e '/regexp/{=;x;1!p;g;$!N;p;D;}' -e h

 # grep for AAA and BBB and CCC (in any order)
 sed '/AAA/!d; /BBB/!d; /CCC/!d'

 # grep for AAA and BBB and CCC (in that order)
 sed '/AAA.*BBB.*CCC/!d'

 # grep for AAA or BBB or CCC (emulates "egrep")
 sed -e '/AAA/b' -e '/BBB/b' -e '/CCC/b' -e d    # most seds
 gsed '/AAA|BBB|CCC/!d'                        # GNU sed only

 # print paragraph if it contains AAA (blank lines separate paragraphs)
 # HHsed v1.5 must insert a 'G;' after 'x;' in the next 3 scripts below
 sed -e '/./{H;$!d;}' -e 'x;/AAA/!d;'

 # print paragraph if it contains AAA and BBB and CCC (in any order)
 sed -e '/./{H;$!d;}' -e 'x;/AAA/!d;/BBB/!d;/CCC/!d'

 # print paragraph if it contains AAA or BBB or CCC
 sed -e '/./{H;$!d;}' -e 'x;/AAA/b' -e '/BBB/b' -e '/CCC/b' -e d
 gsed '/./{H;$!d;};x;/AAA|BBB|CCC/b;d'         # GNU sed only

 # print only lines of 65 characters or longer
 sed -n '/^.{65}/p'

 # print only lines of less than 65 characters
 sed -n '/^.{65}/!p'        # method 1, corresponds to above
 sed '/^.{65}/d'            # method 2, simpler syntax

 # print section of file from regular expression to end of file
 sed -n '/regexp/,$p'

 # print section of file based on line numbers (lines 8-12, inclusive)
 sed -n '8,12p'               # method 1
 sed '8,12!d'                 # method 2

 # print line number 52
 sed -n '52p'                 # method 1
 sed '52!d'                   # method 2
 sed '52q;d'                  # method 3, efficient on large files

 # beginning at line 3, print every 7th line
 gsed -n '3~7p'               # GNU sed only
 sed -n '3,${p;n;n;n;n;n;n;}' # other seds

 # print section of file between two regular expressions (inclusive)
 sed -n '/Iowa/,/Montana/p'             # case sensitive

# SELECTIVE DELETION OF CERTAIN LINES:

 # print all of file EXCEPT section between 2 regular expressions
 sed '/Iowa/,/Montana/d'

 # delete duplicate, consecutive lines from a file (emulates "uniq").
 # First line in a set of duplicate lines is kept, rest are deleted.
 sed '$!N; /^(.*)n1$/!P; D'

 # delete duplicate, nonconsecutive lines from a file. Beware not to
 # overflow the buffer size of the hold space, or else use GNU sed.
 sed -n 'G; s/n/&&/; /^([ -~]*n).*n1/d; s/n//; h; P'

 # delete all lines except duplicate lines (emulates "uniq -d").
 sed '$!N; s/^(.*)n1$/1/; t; D'

 # delete the first 10 lines of a file
 sed '1,10d'

 # delete the last line of a file
 sed '$d'

 # delete the last 2 lines of a file
 sed 'N;$!P;$!D;$d'

 # delete the last 10 lines of a file
 sed -e :a -e '$d;N;2,10ba' -e 'P;D'   # method 1
 sed -n -e :a -e '1,10!{P;N;D;};N;ba'  # method 2

 # delete every 8th line
 gsed '0~8d'                           # GNU sed only
 sed 'n;n;n;n;n;n;n;d;'                # other seds

 # delete lines matching pattern
 sed '/pattern/d'

 # delete ALL blank lines from a file (same as "grep '.' ")
 sed '/^$/d'                           # method 1
 sed '/./!d'                           # method 2

 # delete all CONSECUTIVE blank lines from file except the first; also
 # deletes all blank lines from top and end of file (emulates "cat -s")
 sed '/./,/^$/!d'          # method 1, allows 0 blanks at top, 1 at EOF
 sed '/^$/N;/n$/D'        # method 2, allows 1 blank at top, 0 at EOF

 # delete all CONSECUTIVE blank lines from file except the first 2:
 sed '/^$/N;/n$/N;//D'

 # delete all leading blank lines at top of file
 sed '/./,$!d'

 # delete all trailing blank lines at end of file
 sed -e :a -e '/^n*$/{$d;N;ba' -e '}'  # works on all seds
 sed -e :a -e '/^n*$/N;/n$/ba'        # ditto, except for gsed 3.02.*

 # delete the last line of each paragraph
 sed -n '/^$/{p;h;};/./{x;/./p;}'

# SPECIAL APPLICATIONS:

 # remove nroff overstrikes (char, backspace) from man pages. The 'echo'
 # command may need an -e switch if you use Unix System V or bash shell.
 sed "s/.`echo b`//g"    # double quotes required for Unix environment
 sed 's/.^H//g'             # in bash/tcsh, press Ctrl-V and then Ctrl-H
 sed 's/.x08//g'           # hex expression for sed 1.5, GNU sed, ssed

 # get Usenet/e-mail message header
 sed '/^$/q'                # deletes everything after first blank line

 # get Usenet/e-mail message body
 sed '1,/^$/d'              # deletes everything up to first blank line

 # get Subject header, but remove initial "Subject: " portion
 sed '/^Subject: */!d; s///;q'

 # get return address header
 sed '/^Reply-To:/q; /^From:/h; /./d;g;q'

 # parse out the address proper. Pulls out the e-mail address by itself
 # from the 1-line return address header (see preceding script)
 sed 's/ *(.*)//; s/>.*//; s/.*[:<] *//'

 # add a leading angle bracket and space to each line (quote a message)
 sed 's/^/> /'

 # delete leading angle bracket & space from each line (unquote a message)
 sed 's/^> //'

 # remove most HTML tags (accommodates multiple-line tags)
 sed -e :a -e 's/<[^>]*>//g;/</N;//ba'

 # extract multi-part uuencoded binaries, removing extraneous header
 # info, so that only the uuencoded portion remains. Files passed to
 # sed must be passed in the proper order. Version 1 can be entered
 # from the command line; version 2 can be made into an executable
 # Unix shell script. (Modified from a script by Rahul Dhesi.)
 sed '/^end/,/^begin/d' file1 file2 ... fileX | uudecode   # vers. 1
 sed '/^end/,/^begin/d' "$@" | uudecode                    # vers. 2

 # sort paragraphs of file alphabetically. Paragraphs are separated by blank
 # lines. GNU sed uses v for vertical tab, or any unique char will do.
 sed '/./{H;d;};x;s/n/={NL}=/g' file | sort | sed '1s/={NL}=//;s/={NL}=/n/g'
 gsed '/./{H;d};x;y/n/v/' file | sort | sed '1s/v//;y/v/n/'

 # zip up each .TXT file individually, deleting the source file and
 # setting the name of each .ZIP file to the basename of the .TXT file
 # (under DOS: the "dir /b" switch returns bare filenames in all caps).
 echo @echo off >zipup.bat
 dir /b *.txt | sed "s/^(.*).TXT/pkzip -mo 1 1.TXT/" >>zipup.bat