sed for survival

1. What is sed?
  1) stream editor
    (1) input --(edited)--> output

2. Essential command
  1) s : substitution
    (1) 4 parts of command
      a. s : command
      b. /../../ : delimiter
      c. ^fjdkal : regular expression pattern search pattern
      d. fdjj : replacement string
    (2) Use '/' as a delimiter
      a. '\' : sed 's\/user\/local\/bin/common\/bin' <old >new
      b. '_' : sed 's_/user_/local_/bin_/common_/bin' <old >new
      c. ':' : sed 's:/user:/local:/bin/common:/bin' <old >new
      d. '|' : sed 's|/user/local/bin|common/bin' <old > new
    (3) Use '&' as matched string
      a. add parenthesis to a pattern : sed 's/abc/(&)/' <old <new
        - '&' means pattern, in this command, "abc"

  2) '-e' command
    (1) Combines multiple commands into a single process.

  3) Substitute flags
    (1) /g : global replacement, as in vi

3. Others
  1) File names
    (1) any argument that doesn't start with sed option, it is the file name.

  2) -f : use sed command file
    (1) sed -f sedcommands <old >new

  3) '\' : to divide sed command into multiple lines.

  4) Bourne shall(bash) quote : using ' to quote commands in multiple lines.

  5) Restricting to a line number
    (1) by number : sed '3 s/[0-9][0-9]*//' <old <new
      a. remove the first number in the 3rd line.
    (2) by pattern : sed '/^#/ s/[0-9][0-9]*//' <old <new
      a. remove the first number which is starting with '#'.