Delete lines in Linux: SED, commands

Delete lines in Linux: SED, commands

Unix utility SED provides an effective and 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.

What is the purpose of SED utility?

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.

How to delete one or more lines from a file via SED?

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
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