Delete

-

sed '5d'
Delete line 5

sed '/[Tt]est/d'
Delete all lines containing Test or test

sed 's/...//' data
Delete the first three characters from each line of data
 
sed 's/...$//' data
Delete the last 3 characters from each line of data


Delete all occurrences of a pattern in a file using sed command

This is a simple application of the /s flag where the target string is none.

For example, to remove all occurrences of word "line" in the above file, the sed command would be

bash-3.00# sed 's/line//' textfile.txt
This is  1
This is  2
This is  3
This is  4
This is  5
Note that the word to be replaced upon matching the pattern is none in the above command ('/s/line//')

To remove all occurrences of the character space in the above input file, the sed command would be

bash-3.00# sed 's/ //g' textfile.txt
Thisisline1
Thisisline2
Thisisline3
Thisisline4
Thisisline5
Also note that if you don't use single quotes in the above sed command, then the space pattern should be enclosed in quotes for the command to work.

bash-3.00# sed s/' '//g textfile.txt
Thisisline1
Thisisline2
Thisisline3
Thisisline4
Thisisline5


 Deleting lines which matches a pattern using sed command

To delete lines which matches a pattern, use the /d flag along with the pattern to be matched, for example, to delete lines matching the pattern "line 1" in the above file, the command would be

bash-3.00# sed '/line 1/d' textfile.txt
This is line 2
This is line 3
This is line 4
This is line 5
Now using the above commands, one can also delete the first and last line in a file which matches a pattern.

 Deleting the first line which matches a pattern using sed command

bash-3.00# sed '/line/{1d;}' textfile.txt
This is line 2
This is line 3
This is line 4
This is line 5
In the above command, '1d' is used in braces to indicate that its a command (to delete the specific line, which matches a pattern), this is the way to separate sed flags in command/scripts.

 Deleting the last line which matches a pattern using sed command

bash-3.00# sed '/line/{$d;}' textfile.txt
This is line 1
This is line 2
This is line 3
This is line 4

Comments

Post a Comment

Popular posts from this blog

Standard Error

-
In  addition to standard input and standard output, there is another place known as  standard error. This is where most Unix commands write their error messages. And as with the other two "standard" places, standard error is associated with your terminal by default. In most cases, you never know the difference between standard output and standard error: [root@server1 ~]# ls n* ls: n*: No such file or directory  [root@server1 ~]# ls n* > foo ls: n*: No such file or directory You can also redirect standard error to a file by using the notation command 2> file No space is permitted between the 2 and the > . Any error messages normally intended for standard error will be diverted into the specified file , similar to the way standard output gets redirected. [root@server1 ~]# ls n* 2> errors [root@server1 ~]# cat errors ls: n*: No such file or directory
Read more

Shell Basic Operators.

-
There are various operators supported by each shell. There are following operators which we are going to discuss: Arithmetic Operators. Relational Operators. Boolean Operators. String Operators. File Test Operators. The Bourne shell didn't originally have any mechanism to perform simple arithmetic but it uses external programs, either  awk  or the must simpler program  expr . Here is simple example to add two numbers: #!/bin/sh val=`expr 2 + 2` echo "Total value : $val" This would produce following result: Total value : 4 There are following points to note down: There must be spaces between operators and expressions for example 2+2 is not correct, where as it should be written as 2 + 2. Complete expresssion should be enclosed between  `` , called inverted commas. Arithmetic Operators: There are following arithmatic operators supported by Bourne Shell. Assume variable a holds 10 and variable b holds...
Read more

AWK

-
AWK Structure pattern {action} BEGIN and END patterns in the AWK BEGIN { print “BEGIN” } { print } END   { print “END”  } # cat textfile.txt  Ashish 123 Ashi     456 Ash      789 A          000 # awk '{print $1}' textfile.txt  Ashish Ashi Ash A # awk '{print $2}' textfile.txt  123 456 789 000 # awk '{print $2,$1}' textfile.txt  123 Ashish 456 Ashi 789 Ash 000 A If the file is seperated with some delimeter, then we make use of -F for awk. In the below example, the input file is using the pipe ( | ) as delimiter. # cat textfile.txt  Ashish|123 Ashi|456 Ash|789 A|000 Ashish|007 # awk -F\| '{print $1}' textfile.txt  Ashish Ashi Ash A Ashish # awk -F\| '{print $2}' textfile.txt  123 456 789 000 007 # awk -F\| '{print $2,$1}' textfile.txt  123 Ashish 456 Ashi 789 Ash 000 A 007 Ashish # awk...
Read more