How to use the sed command to filter text files in Linux and other useful shell tricks for the Linux command line.

Posted: October 11, 2017. At: 11:26 PM. This was 3 months ago. Post ID: 4705
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Using sed to filter a text file and change a specific character for another. In this case the ” character becomes the ‘ character using the magic of the sed command. Since I am using a character the shell also uses I have to escape it out so the command will work. This can make for a complex regex when you are building a Regular Expression.

jason@jason-desktop:~/Documents$ sed "s/\"/\'/gi;" setup-ad-server.ps1 
# Windows PowerShell script for AD DS Deployment
Import-Module ADDSDeployment
Install-ADDSForest `
-CreateDnsDelegation:$false `
-DatabasePath 'C:\Windows\NTDS' `
-DomainMode 'Win2012' `
-DomainName 'john.local' `
-DomainNetbiosName 'JOHN' `
-ForestMode 'Win2012' `
-InstallDns:$true `
-LogPath 'C:\Windows\NTDS' `
-NoRebootOnCompletion:$false `
-SysvolPath 'C:\Windows\SYSVOL' `

Here is another example. Substituting one character for a whole word. The sed command can manage this easily.

jason@jason-desktop:~/Documents$ uname -a | sed "s/\#/Number: /gi;"
Linux jason-desktop 4.10.0-35-generic Number: 39-Ubuntu SMP Wed Sep 13 07:46:59 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

To list all jpg files in a folder that start with “IMG” and end with the “*.jpg” extension use this command.

ls -hula IMG**.jpg

And you will get this output.

-rw-r--r-- 1 john john 293K  08-10-12 02:15 pm IMG-20121008-00046.jpg
-rw-r--r-- 1 john john 295K  11-10-12 10:07 pm IMG-20121008-00047.jpg
-rw-r--r-- 1 john john 278K  11-10-12 10:07 pm IMG-20121008-00048.jpg

if you further refine the command and add more to it; then you can refine the file listing down to one single file.

ls -hula IMG*47*.jpg

This time only one file is returned in the listing.

-rw-r--r-- 1 john john 295K  11-10-12 10:07 pm IMG-20121008-00047.jpg

This is a very good trick for listing only certain files in a directory listing using ls. Below is a further refinement of our ls command. The bash shell is very flexible when you are searching for files in a folder. Imagine if there are thousands of files in the folder and you are only looking for one specific file…

[ john@3.2.0-2-486 ]
[ Jobs 0.PWD: ~/Desktop.bash 4.2.20. ] [ 2 ]
[ 22:29:38 ]
[ $ ]-> ls -hula IMG*-*46*.jpg
-rw-r--r-- 1 john john 293K  08-10-12 02:15 pm IMG-20121008-00046.jpg

Here is another usage; looking for desktop screenshots from a specific time.

[flynn@flynn-grid-runner Pictures]$ ls -hula Screen*00:34:49*.png
-rw-rw-r-- 1 flynn flynn 304K  04-10-12 03:04 pm Screenshot from 2012-09-19 00:34:49.png

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