Sed rewamped

Sed reads its input from stdin (i.e., the console) or from files (or both), and sends the results to stdout (console or screen).

Sed's normal behavior is to print the entire file, including the parts that haven't been altered, unless you use the -n switch.

The "-n" stands for "no output".
This switch is almost always used in conjunction with a 'p' command somewhere, which says to print only the sections of the file that have been specified.

- When you want ti review only few lines of file. use this, This will display first 3 lines.
sed -n 1,3p file - # the 'p' stands for print

- Likewise, sed could show me everything else BUT those particular lines, without physically changing the file on the disk,
sed 1,3d file # the 'd' stands for delete


- An exclamation mark '!' after a regex ('/RE/!') or line number will select all lines that do NOT match that address.
. ^ $ [ ] { } ( ) ? + *

Three things are interpolated: ampersand (&), backreferences, and options for special seds.

An ampersand on the RHS is replaced by the entire expression matched on the LHS. There is never any reason to use grouping like this:
s/\(some-complex-regex\)/one two \1 three/

since you can do this instead:
s/some-complex-regex/one two & three/

- Substitution switches

Standard versions of sed support 4 main flags or switches which may be added to the end of an "s///" command. They are:
N - Replace the Nth match of the pattern on the LHS, where N is an integer between 1 and 512. If N is omitted, the default is to replace the first match only.
g - Global replace of all matches to the pattern.
p - Print the results to stdout, even if -n switch is used.
w file - Write the pattern space to 'file' if a replacement was done. If the file already exists when the script is executed, it is overwritten. During script execution, w appends to the file for each match.


SED ONE LINERS

- sed G file - Double space a file
- sed 'G;G' file - # Triple space a file
- sed 's/^[ ^t]*//' file # Delete leading whitespace (spaces/tabs) from end of each line.
- sed 's/[ ^t]*$//' file # Delete trailing whitespace (spaces/tabs) from end of each line.
- sed 's/^[ ^t]*//;s/[ ^]*$//' file # Delete BOTH leading and trailing whitespace from each line
- sed 's/foo/bar/' file # replaces only 1st instance in a line
- sed 's/foo/bar/4' file # replaces only 4th instance in a line
- sed 's/foo/bar/g' file # replaces ALL instances within a line
- sed -e :a -e '/\\$/N; s/\\\n//; ta' file # If a line ends with a backslash, join the next line to it.


Addressing and address ranges
Sed commands may have an optional "address" or "address range" prefix. If there is no address or address range given, then the command is applied to all the lines of the input file or text stream.

5d # delete line 5 only
5!d # delete every line except line 5
/RE/s/LHS/RHS/g # substitute only if RE occurs on the line
/^$/b label # if the line is blank, branch to ':label'
/./!b label # ... another way to write the same command
\%.%!b label # ... yet another way to write this command
$!N # on all lines but the last, get the Next line
/tape$/ # matches the word 'tape' at the end of a line
/tape$deck/ # matches the word 'tape$deck' with a literal '$'
/tape\ndeck/ # matches 'tape' and 'deck' with a newline between