5.10. sed Scripting

A sed script is a list of sed commands in a file. To let sed know your commands are in a file, when invoking sed at the command line, use the –f option followed by the name of the sed script. Sed is very particular about the way you type lines into the script. There cannot be any trailing whitespace or text at the end of the command. If commands are not placed on a line by themselves, they must be terminated with a semicolon. A line from the input file is copied into the pattern buffer, and all commands in the sed script are executed on that line. After the line has been processed, the next line from the input file is placed in the pattern buffer, and all commands in the script are executed on that line. Sed gets "garbled" if your syntax is incorrect.

The nice thing about sed scripts is that you don't have to worry about the shell's interaction as you do when at the command line. Quotes are not needed to protect sed commands from interpretation by the shell and only one backslash is used in line continuation. In fact, you cannot use quotes in a sed script at all, unless they are part of a search pattern.

The examples in this section use the following datafile.

% cat datafile
northwest	NW	Charles Main	3.0	.98	3	34
western	WE	Sharon Gray	5.3	.97	5	23
southwest	SW	Lewis Dalsass	2.7	.8	2	18
southern	SO	Suan Chin	5.1	.95	4	15
southeast	SE	Patricia Hemenway	4.0	.7	4	17
eastern	EA	TB Savage	4.4	.84	5	20
northeast	NE	AM Main Jr.	5.1	.94	3	13
north	NO	Margot Weber	4.5	.89	5	9
central	CT	Ann Stephens	5.7	.94	5	13

5.10.1 sed Script Examples

Example 5.38.

% cat sedding1                    # Look at the contents of the sed script

1   # My first sed script by Jack Sprat

2   /Lewis/a\

3       Lewis is the TOP Salesperson for April!!\

        Lewis is moving to the southern district next month.\

4       CONGRATULATIONS!

5   /Margot/c\

        *******************\

        MARGOT HAS RETIRED\

        ********************

6   1i\

    EMPLOYEE DATABASE\

    –––––––––––––––––––––

7   $d



% sed –f sedding1 datafile   # Execute the sed script commands; input file is datafile

EMPLOYEE DATABASE

––––––––––––––––––---

northwest             NW         Charles Main          3.0   .98     3     34

western               WE         Sharon Gray           5.3   .97     5     23

southwest             SW         Lewis Dalsass         2.7   .8      2     18

Lewis is the TOP Salesperson for April!!

Lewis is moving to the southern district next month.

CONGRATULATIONS!

southern              SO         Suan Chin             5.1   .95     4     15

southeast             SE         Patricia Hemenway     4.0   .7      4     17

eastern               EA         TB Savage             4.4   .84     5     20

northeast             NE         AM Main Jr.           5.1   .94     3     13



********************

MARGOT HAS RETIRED

*****************

EXPLANATION

Example 5.39.

%  cat sedding2             # Look at the contents of the sed script

# This script demonstrates the use of curly braces to nest addresses

# and commands. Comments are preceded by a pound sign (#) and must

# be on a line by themselves. Commands are terminated with a newline

# or semicolon.  If there is any text after a command, even one

# space, you receive an error message:

#      sed: Extra text at end of command:



1   /western/, /southeast/{

        /^ *$/d

        /Suan/{ h; d; }

    }

2   /Ann/g

3   s/TB \(Savage\)/Thomas \1/

4 % sed -f sedding2 datafile

northwest             NW      Charles Main        3.0   .98    3   34

western               WE      Sharon Gray         5.3   .97    5   23

southwest             SW      Lewis Dalsass       2.7   .8     2   18

southeast             SE      Patricia Hemenway   4.0   .7     4   17

eastern               EA      Thomas Savage       4.4   .84    5   20

northeast             NE      AM Main Jr.         5.1   .94    3   13

north                 NO      Margot Weber        4.5   .89    5    9

southern              SO      Suan Chin           5.1   .95    4   15

EXPLANATION

5.10.2 sed Review

Table 5.4 lists sed commands and what they do.

Table 5.4. sed Review

Command	What It Does
sed –n '/sentimental/p' filex	Prints to the screen all lines containing sentimental. The file filex does not change. Without the –n option, all lines with sentimental will be printed twice.
sed '1,3d' filex > newfilex	Deletes lines 1, 2, and 3 from filex and saves changes in newfilex.
sed '/[Dd]aniel/d' filex	Deletes lines containing Daniel or daniel.
sed –n '15,20p' filex	Prints only lines 15 through 20.
sed '1,10s/Montana/MT/g' filex	Substitutes Montana with MT globally in lines 1 through 10.
sed '/March/\!d' filex    (csh) sed '/March/!d' filex     (sh)	Deletes all lines not containing March. (The backslash is used only in the csh to escape the history character.)
sed '/report/s/5/8/' filex	Changes the first occurrence of 5 to 8 on all lines containing report.
sed 's/....//' filex	Deletes the first four characters of each line.
sed 's/...$//' filex	Deletes the last three characters of each line.
sed '/east/,/west/s/North/South/' filex	For any lines falling in the range from east to west, substitutes North with South.
sed –n '/Time off/w timefile' filex	Writes all lines containing Time off to the file timefile.
sed 's/\([Oo]ccur\)ence/\1rence/' file	Substitutes either Occurence or occurence with Occurrence or occurrence.
sed –n 'l' filex	Prints all lines showing nonprinting characters as \nn, where nn is the octal value of the character, and showing tabs as >.