SED (Stream Editor)
Syntex:-
Sed options ‘address
action’ file(s)
Sed uses instruction to act on text. An
instruction combines an address for selecting lines,with an action to be taken
on them.
Command : s for
Substitution
Sed has several commands, but most people only learn the substitute command: s. The substitute command changes all occurrences of the regular expression into a new value. A simple example is changing "day" in the "old" file to "night" in the "new" file:
sed s/day/night/ old >new
If you have meta-characters in the command, quotes are necessary. And if you aren't sure, it's a good habit, and I will henceforth quote future examples to emphasize the "best practice." Using the strong (single quote) character, that would be:
sed 's/day/night/'
old >new
There are four parts to this substitute command:
s Substitute command
/../../ Delimiter
day Regular Expression Pattern Search Pattern
night Replacement string
Slash as a delimiter:-
If you want to change a pathname that contains a slash - say /usr/local/bin to /common/bin you could use “|” to quote the slash:-
sed 's|/usr/local/bin|/common/bin|' <old >new
Using & as a matched String:-
Sometimes you want to search for a pattern and add some characters, like parenthesis, around or near the pattern you found. It is easy to do this if you are looking for a particular string:
sed 's/abc/(abc)/' <old >new This will not work
The solution requires the special character "&." It corresponds to the pattern found.
sed
's/[a-z]*/(&)/' <old >new
Substitution flag:-
/g - Global Replacement:-
Most Unix utilties work on files, reading a line at a time. Sed, by default, is the same way. If you tell it to change a word, it will only change the first occurrence of the word on a line. You may want to make the change on every word on the line instead of the first.If you want it to make changes for every word, add a "g" after the last delimiter and use the work-around:
sed 's/[^ ][^ ]*/(&)/g' <old >new
/1,/2,etc. Specifying Which occurance:-
If you want to modify a particular pattern
that is not the first one on the line,if you want to delete the second word on
the line then use this command:-
sed
's/[a-zA-Z]* //2' <old >new
You can add a number after the substitution
command to indicate you only want to match that particular pattern.
You can combine a number with the g
(global) flag. For instance, if you want to leave the first world alone , but
change the second, third, etc. to DELETED, use /2g:
sed
's/[a-zA-Z]* /DELETED /2g' <old >new
There is one more flag that can follow the
third delimiter. With it, you can specify a file that will receive the modified
data. An example is the following, which will write all lines that start with
an even number to the file even:
sed
-n 's/^[0-9]*[02468] /&/w even' <file
You must have exactly one space between the
w and the filename.
Ex:-
1)
sed –n ‘1,500w foo1 ---Saves 1 to 500 to foo1
501,$w foo2’
foo.main ----- from 501 to last
line to foo2
Multiple Command with –e command:-
One method of combining multiple commands is to use a -e before each command:
sed -e 's/a/A/' -e 's/b/B/' <old >new
Filenames On the Command Line:-
You can specify files on the command line
if you wish.
sed
-e 's/^#.*//' f1 f2 f3 | grep -v '^$' | wc –l
The sed substitute command changes
every line that starts with a "#" into a blank line.
Grep was
used to filter out empty lines.
Wc counts
the number of lines left.
Note :-^ sign shows start line.
$ shows end of the line.
Sed –n Option:-No Printing
The "-n" option will not print
anything unless an explicit request to print is found.
Eg:-
sed –n ‘1,2p’ <filename>
This command will print the first two lines
of file( head -2 <filename>)
sed –n ‘$p’ <filename >
Print the last line .( tail -1
<filename>)
Negating
the Action:-
Sed
–n ‘3,$!p’ <filename> Don’t print from line 3 to end
Deleting Line:- sed use –d (delete) command to emulate grep –v option of selection lines not containing the pattern .
e.g.
Sed ‘/director/d’ emp.lst >olist
Sed –n ‘/director/!p’ emp.lst > olist ( -n option is not used with d )
Pattern:-
Sed uses the same convention, provided you terminate the expression with a slash.
To delete the first number on all lines that start with a "#," use:
sed '/^#/ s/[0-9][0-9]*//'
Suppose you wanted to search for the string
"/usr/local/bin" and you wanted to
change it for "/common/all/bin." You
could use the backslash to escape the slash:
sed '/\/usr\/local\/bin/ s/\/usr\/local/\/common\/all/'
sed 's/foo/bar/g' filename # standard replace command
sed '/foo/ s/foo/bar/g' filename # executes more quickly
Range By Line Number:-
sed '1,100 s/A/a/'
Range By Pattern:-
sed '/start/,/stop/ s/#.*//'
This example will remove comments everywhere except the lines between the two keywords:
sed -e '1,/start/
s/#.*//' -e '/stop/,$ s/#.*//'
eg:-
sed -e 's/#.*//' -e '/^$/ d' (Removing comments and blank lines takes two commands. The first removes every character from the "#" to the end of the line, and the second deletes all blank lines: )
Sed Range Command Results
--------------------------------------------------------
sed -n 1,10 p Print first 10 lines (head -10)
sed -n 11,$ !p Print first 10 lines
sed 1,10 !d Print first 10 lines
sed 11,$ d Print first 10 lines
--------------------------------------------------------
sed -n 1,10 !p Print last 10 lines (tail -10 )
sed -n 11,$ p Print last 10 lines
sed 1,10 d Print last 10 lines
sed 11,$ !d Print last 10 lines
--------------------------------------------------------
sed -n 1,10 d Nothing printed
sed -n 1,10 !d Nothing printed
sed -n 11,$ d Nothing printed
sed -n 11,$ !d Nothing printed
--------------------------------------------------------
sed 1,10 p Print first 10 lines twice,
Then next 10 lines once
sed 11,$ !p Print first 10 lines twice,
Then last 10 lines once
--------------------------------------------------------
sed 1,10 !p Print first 10 lines once,
Then last 10 lines twice
sed 11,$ p Print first 10 lines once,
then last 10 lines twice
Hand-on sed:-
#
double space a file
sed G
#
triple space a file
sed 'G;G'
#
count lines (emulates "wc -l")
sed -n '$='
# Remove ^M character
#in bash/tcsh, press Ctrl-V then Ctrl-M
sed
'1,$ s/^M//g' filename
# delete leading
whitespace (spaces, tabs) from front of each line
# aligns all text flush left
sed 's/^[
\t]*//' # see note on '\t' at end of file
# delete trailing whitespace (spaces, tabs)
from end of each line
sed 's/[ \t]*$//' # see note on '\t' at end of file
# delete BOTH leading and trailing
whitespace from each line
sed 's/^[ \t]*//;s/[ \t]*$//'
# substitute (find and replace)
"foo" with "bar" on each line
sed 's/foo/bar/' # replaces only 1st instance in a
line
sed 's/foo/bar/4' # replaces only 4th instance in a
line
sed 's/foo/bar/g' # replaces ALL instances in a line
sed 's/\(.*\)foo\(.*foo\)/\1bar\2/' # replace the next-to-last case
sed 's/\(.*\)foo/\1bar/' # replace only the
last case
sed '/baz/s/foo/bar/g'
# substitute "foo" with
"bar" EXCEPT for lines which contain "baz"
sed '/baz/!s/foo/bar/g'
#
print the line immediately before a regexp, but not the line
#
containing the regexp
sed -n '/regexp/{g;1!p;};h'
#
print the line immediately after a regexp, but not the line
#
containing the regexp
sed -n '/regexp/{n;p;}'
sed -n '/^.\{65\}/p'
# print only lines of less than 65
characters
sed -n '/^.\{65\}/!p'
#
print line number 52
sed -n '52p' #
method 1
sed '52!d' #
method 2
sed '52q;d' #
method 3, efficient on large files
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