Delete Lines from a File Using Sed

December 2016

Unix utility SED provides an effective and a versatile way of deleting one or more lines from a designated file to match the needs of the user.

This Unix command is used for command line processing. This utility can be used to delete expressions from a file which can be identified by a specifying delimiter (such as a comma, tab, or space), by line number, or by searching for a string, expression or the address of a line in the syntax of Sed.

Sed: Delete One or More Lines from a File

Here is how to remove one or more lines from a file.

Syntax

sed '{[/]<n>|<string>|<regex>[/]}d' <fileName>       
sed '{[/]<adr1>[,<adr2>][/]d' <fileName>


/.../=delimiters

n = line number

string = string found in in line

regex = regular expression corresponding to the searched pattern

addr = address of a line (number or pattern )

d = delete

Examples of Sed

Here are some examples of how to use the above syntax.


Use the following code to remove the third line:
sed '3d' fileName.txt

Remove the line containing the string "awk," by using:
sed '/awk/d' filename.txt

You can remove the last line by typing in:
sed '$d' filename.txt

Or remove all empty lines through:
sed '/^$/d' filename.txt       
sed '/./!d' filename.txt

Remove the line matching by a regular expression (by eliminating one containing digital characters, at least 1 digit, located at the end of the line):
sed '/[0-9/][0-9]*$/d' filename.txt

Remove the interval between lines 7 and 9:
sed '7,9d' filename.txt 

The same operation as above but replacing the address with parameters:
sed '/-Start/,/-End/d' filename.txt

The above examples are only changed at the display of the file (stdout1= screen).

For permanent changes to the old versions (<4) use a temporary file for GNU sed using the "-i[suffix]":
sed -i".bak" '3d' filename.txt

Related :

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