The sed full form is a “Stream EDitor”. This sed command is UNIX utility. A “non-interactive” text editor that could be called from the UNIX command line. It input text flows through the program, is modified, and is directed to standard output.
An Example: The following sentence is input to the sed program:
echo "Install and ruining the WebLogic for a Middleware application operation." |
sed 's/ruining/running/‘
Install and running the WebLogic for a Middleware application operation..
Eliminate the tedium of routine editing tasks! (find, replace, delete, append, insert)
… but your word processor can already do that right? It is Wrong! Because the sed is extremely powerful and it comes with every UNIX flavor operating system in the world!
Hope now you will understand why you need sed with the following three cases:
1. To edit files too large for comfortable interactive editing;
2. To edit any size file when the sequence of editing commands is too complicated to be comfortably typed in interactive mode.
3. To perform multiple `global' editing functions efficiently in one pass through the input.
The sed Architecture is as follows:
Pattern space: Workspace or temporary buffer where a single line of input is held while the editing commands are applied
Hold space: Secondary temporary buffer for temporary storage only
Let me put it in program sudo code way:
While (read line){
1 ) reads an input line from STDIN or
a given file, one line at a time, into the pattern space.
Pattern Space = a data buffer - the “current text” as it’s being edited
2) For each line, sed executes a series of editing commands issued by user on the pattern space.
3) Writes back the pattern space to STDOUT.
}
Example 2:
echo “Vasu enjoys hiking and Raghav enjoys skiing” |sed –e ‘s/skiing/hiking/g; s/hiking/biking/g’
1 ) Here the sed reads the line “Vasu enjoys hiking and Raghav enjoys skiing” and executed the first ‘substitute’ command.
The resulting line – in the pattern space:
2) Then the second substitute command is executed on the line in the pattern space, and the result is :
3) finally, the result is written to standard output.
Since only a few lines of the input reside in memory at one time, and no temporary files are used, the effective size of file that can be edited is limited only by the requirement that the input and output fit simultaneously into available on the hard disk.
-e an "in-line" script, i.e. a script to sed execute given on the command line. Multiple command line scripts can be given, each with an -e option.
-n by default, sed writes each line to stdout when it reaches the end of the script (being whatever on the line) this option prevents that. i.e. no output unless there is a command to order SED specifically to do it
-f read scripts from specified file, several -f options can appear
Files are the files to read, if a "-" appears, read from stdin,if no files are given, read also from stdin
Different ways to Invoke Sed:
sed –e 'command;command;command' input_file > output_file save results
.... | sed –e 'command;command;command' | .... use in a pipeline
sed -f sedcommands input_file > output_file commands are in file somewhere else
1. sed commands are usually on one line
2. if we want more (multi-line commands), then we must end the first line with an `\'
3. if a command is one line only, it can be separated by a `;‘
4. if it is a multi-line, then it must contain all of its line (except the first) by themselves
5. on command line, what follows a `-e' is like a whole line in a sed script
a append
c change lines
d delete lines
i insert
p print lines
s substitute
Syntax for these commands is a little strange because they must be specified on multiple lines
append [address]a\
text
insert [address]i\
text
change [address(es)]c\
text
append/insert for single lines only, not range
Append places text after the current line in pattern space
Insert places text before the current line in pattern space
Each of these commands requires a \ following it.
text must begin on the next line.
If text begins with whitespace, sed will discard it
unless you start the line with a \
Example:
/<Insert Text Here>/i\
Line 1 of inserted text\
\ Line 2 of inserted text
would leave the following in the pattern space
Line 1 of inserted text
Line 2 of inserted text
<Insert Text Here>
Unlike Insert and Append, Change can be applied to either a single line address or a range of addresses
When applied to a range, the entire range is replaced by text specified with change, not each line
Exception: If the Change command is executed with other commands enclosed in { } that act on a range of lines, each line will be replaced with text
No subsequent editing allowed
Remove mail headers, ie; the address specifies a range of lines beginning with a line that begins with From until the first blank line.
The first example replaces all lines with a single occurrence of <Mail Header Removed>.
The second example replaces each line with <Mail Header Removed>
If an address is followed by an exclamation point (!), the associated command is applied to all lines that don’t match the address or address range
Examples:
1,5!d would delete all lines except 1 through 5
/black/!s/cow/horse/ would substitute “horse” for “cow” on all lines except those that contained “black”
“The brown cow” -> “The brown horse”
“The black cow” -> “The black cow”
The Print command (p) can be used to force the pattern space to be output, useful if the -n option has been specified
Syntax: [address1[,address2]]p
Note: if the -n option has not been specified, p will cause the line to be output twice!
Examples:
1,5p will display lines 1 through 5
/^$/,$p will display the lines from the first blank line through the last line of the file
Syntax: [address(es)]s/pattern/replacement/[flags]
pattern - search pattern
replacement - replacement string for pattern
flags - optionally any of the following
n a number from 1 to 512 indicating which occurrence of pattern should be replaced
g global, replace all occurrences of pattern in pattern space
p print contents of pattern space
The sed command for substitute patterns
s/Puff Daddy/P. Diddy/
Substitute P. Diddy for the first occurrence of Puff Daddy in pattern space
s/Tom/Dick/2
Substitutes Dick for the second occurrence of Tom in the pattern space
s/wood/plastic/p
Substitutes plastic for the first occurrence of wood and outputs (prints) pattern space
Substitute can use several special characters in the replacement string
& - replaced by the entire string matched in the regular expression for pattern
\n - replaced by the nth substring (or subexpression) previously specified using “\(“ and “\)”
\ - used to escape the ampersand (&) and the backslash (\)
"the UNIX operating system …"
s/.NI./wonderful &/
"the wonderful UNIX operating system …"
Let us operate on the file with sed command
cat test1
first:second
one:two
sed 's/\(.*\):\(.*\)/\2:\1/' test1
second:first
two:one
sed 's/\([[:alpha:]]\)\([^ \n]*\)/\2\1ay/g'
Pig Latin ("unix is fun" -> "nixuay siay unfay")
The Transform command (y) operates like tr, it does a one-to-one or character-to-character replacement
Transform accepts zero, one or two addresses
[address[,address]]y/abc/xyz/
every a within the specified address(es) is transformed to an x. The same is true for b to y and c to z
y/abcdefghijklmnopqrstuvwxyz/ABCDEFGHIJKLMNOPQRSTUVWXYZ/ changes all lower case characters on the addressed line to upper case
If you only want to transform specific characters (or a word) in the line, it is much more difficult and requires use of the hold space
Quit causes sed to stop reading new input lines and stop sending them to standard output
It takes at most a single line address
Once a line matching the address is reached, the script will be terminated
This can be used to save time when you only want to process some portion of the beginning of a file
Example: to print the first 100 lines of a file (like head) use:
sed '100q' filename
sed will, by default, send the first 100 lines of filename to standard output and then quit processing
Sed Advantages
^ matches the beginning of the line
$ matches the end of the line
. Matches any single character
\ Escapes any metacharacter that follows, including itself.
(character)* Match arbitrarily many occurences of (character)
(character)? Match 0 or 1 instance of (character)
(character)+ Match 1 or more instances of (character)
[abcdef] Match any character enclosed in [ ] (in this instance, a b c d e or f)
[^abcdef] Match any character NOT enclosed in [ ]
(character)\{m,n\} Match m-n repetitions of (character)
(character)\{m,\} Match m or more repetitions of (character)
(character)\{,n\} Match n or less (possibly 0) repetitions of (character)
(character)\{n\} Match exactly n repetitions of (character)
\{n,m\} range of occurrences, n and m are integers
\(expression\) Group operator.
expression1|expression2 Matches expression1 or expression 2.
() groups regular expressions
Regular Expressions (character classes)
The following character classes are short-hand for matching special characters.
[:alnum:] Printable characters (includes white space)
[:alpha:] Alphabetic characters
[:blank:] Space and tab characters
[:cntrl:] Control characters
[:digit:] Numeric characters
[:graph:] Printable and visible (non-space) characters
[:lower:] Lowercase characters
[:print:] Alphanumeric characters
[:punct:] Punctuation characters
[:space:] Whitespace characters
[:upper:] Uppercase characters
[:xdigit:] Hexadecimal digits
Hard to remember text from one line to another
Not possible to go backward in the file
No way to do forward references like /..../+1
No facilities to manipulate numbers
Cumbersome syntax
SED reference: http://www.codewalkers.com/c/a/Server-Administration/Stream-Editor-in-the-UNIX-Shell/
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