sed

A sed (stream editor) command consists of a range, the command name (a single letter), and arguments if apropriate. If the range is absent the command operates on all input lines. By default sed writes all input lines to STDOUT. All sed commands should be quoted to prevent special characters from being interpreted by the shell.

A few sed options:

-e

edit (command follows)

-f

file of edit commands (name follows)

-n

do not print by default

-r

use extended regular expressions

A few sed range specifiers:

/regexp/

command works on all lines matching regexp

/regexp/!

command works on all lines not matching regexp

/regexp1/,/regexp2/

command works on lines from the first matching regexp1 to the next matching regexp2

A few sed command forms:

s/regexp/string/

substitute string for the first occurrence of regexp on the input line

s/regexp/string/n

substitute string for the nth occurrence of regexp on the input line

s/regexp/string/g

substitute string for all occurrences of regexp on the input line (global)

d

delete the input line

p

print the input line

head -n25 /etc/passwd | sed -e 's/shutdown//' # delete 1st shutdown head -n25 /etc/passwd | sed -e 's/shutdown/XX/' # change 1st shutdown to XX head -n25 /etc/passwd | sed -e 's/shutdown/XX/2' # change 2nd shutdown head -n25 /etc/passwd | sed -e 's/shutdown/XX/g' # every shutdown head -n25 /etc/passwd | sed -e 's/shutdown/XX/g' -e 's/:/#/g' # two edits head -n25 /etc/passwd | sed -e '/false$/s/:/#/g' # only lines ending false head -n25 /etc/passwd | sed -e '/false$/!s/:/#/g' # lines not ending false head -n25 /etc/passwd | sed -e '/^lp:/,/^ftp:/s/:/#/g' # range of lines head -n25 /etc/passwd | sed -e '/^lp:/,/^ftp:/d' # delete range of lines touch F1.old F2.old F3.old # create three files ls F[123].* ls F[123].* | sed -e 's/\.old$/.new/' # change extensions .old to .new ls F[123].* | sed -e 'p' -e 's/\.old$/.new/' # also print original names # next line passes the list of arguments to mv, no more than 2 at a time ls F[123].* | sed -e 'p' -e 's/\.old$/.new/' | xargs -n2 mv ls F[123].* # files are renamed rm F[123] # clean up