Sed - Delete one or more lines from a file
Syntax:
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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
Remove the 3rd line:
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sed '3d' fileName.txt
Remove the line containing the string "awk":
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sed '/awk/d' filename.txt
Remove the last line:
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sed '$d' filename.txt
Remove all empty lines:
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sed '/^$/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):
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sed '/[0-9/][0-9]*$/d' filename.txt
Remove the interval between lines 7 and 9:
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sed '7,9d' filename.txt
The same operation as above but replacing the address with parameters:
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sed '/-Start/,/-End/d' filename.txt
The above examples are only changed at the display of the file (stdout1= screen).
For permanent changes to the old versions (<4) use a temporary file for GNU sed using the "-i[suffix]":
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sed -i".bak" '3d' filename.txt
Task: Remove blank lines using sed
Type the following command:
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$ sed '/^$/d' input.txt > output.txt
Task: Remove blank lines using grep
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$ grep -v '^$' input.txt > output.txt
Both grep and sed use special pattern ^$ that matchs the blank lines. Grep -v option means print all lines except blank line.
Let us say directory /home/me/data/*.txt has all text file. Use following for loop (shell script) to remove all blank lines from all files stored in /home/me/data directory:
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#!/bin/sh
files="/home/me/data/*.txt"
for i in $files
do
sed '/^$/d' $i > $i.out
mv $i.out $i
done
Updated for accuracy.
