command sed stream editor

info

1. sed short for stream editor

2. filter and transform text

advanced demo

1. sed substitution delimiter

   1. @ delimiter

       $ sed 's@/path/to/file@/path/toto/file@g' path.txt
      

   2. / delimiter

       $ sed 's/\/path\/to\/file/\/path\/toto\/file/g' path.txt
      

2. sed & get matched string

   1. substitute usr/bin to usr/bin/local

       $ sed 's@/usr/bin@&local@g' path.txt
       # & in the replacement part
       # will be replace with `/usr/bin`
      

   2. match the whole line

       # & replaces whatever matches with give regexp
       $ sed 's@^.*$@<<<&>>>@g' path.txt
       # `^.*$` matches the whole line
      

3. grouping and back-references

   1. get only the first path in each line

       $ sed 's/\(\/[^:]*\).*/\1/g' path.txt
       # `\(\/[^:]*\)` matches the path
       # avaiale before first `:` comes
       # `\1` replaces the first matched group
      

   2. multigrouping

       $ sed '$s@\([^:]*\):\([^:]*\):\([^:]*\)@\3:\2:\1@g' path.txt
      

   3. get the list of usernames in /etc/passwd file

       $ sed 's/\([^:]*\).*/\1/' /etc/passwd
      

   4. parenthesize first character of each word

       $ echo "Welcome To The Geek Stuff" | sed 's/\(\b[A-Z]\)/\(1\)/g'
      

   5. commify the simple numbers

       $ cat numbers
       1234
       12121
       3434
       123
      
       $ sed 's/\(^\|[^0-9.]\)\([0-9]\+\)\([0-9]\{3\}\)/\1\2,\3/g' numbers