Open-source News

Feren OS is a Linux distribution that is as lovely as it is easy to use  ZDNet

Linux Mint 21 arrives. Here's what's new  ZDNet

Linux Mint 21 arrives. Here's what's new  ZDNet

Linux Mint 21 Released  Tom's Hardware

Linux 6.0 To Disable Printing On Consoles With Real-Time Kernels  Phoronix

As part of getting PREEMPT_RT support ready to be mainlined at long last for real-time kernel builds, a number of Linux 6.0 (nee 5.20) pull requests have revolved around additional RT preparatory changes. With the printk changes for Linux 6.0, the console drivers will now be skipped in RT mode...

How I use the Linux sed command to automate file edits Jim Hall Tue, 08/02/2022 - 03:00 1 reader likes this 1 reader likes this

When I use the Linux command line, whether I'm writing a new program on my desktop computer or managing a website on my web server, I often need to process text files. Linux provides powerful tools that I leverage to get my work done. I frequently use sed, an editor that can modify text according to a pattern.

sed stands for stream editor, and it edits text in a file and prints the results. One way to use sed is to identify several occurrences of one string in a file and replace them with a different string. You can use sed to process text files to a seemingly endless degree, but I'd like to share a few ways I use sed to help me manage files.

Search and replace text in a file on Linux

To use sed, you need to use a regular expression. A regular expression is a set of special characters that define a pattern. My most frequent example of using sed is replacing text in a file. The syntax for replacing text looks like this: s/originaltext/newtext/. The s tells sed to perform text replacement or swap occurrences of text. Provide the original text and new text between slashes.

This syntax will only replace the first occurrence of originaltext on each line. To replace every occurrence, even if the original text appears more than once on a line, append g to the end of the expression. Here is an example: s/originaltext/newtext/g.

To use this with sed, specify this regular expression with the -e option:

$ sed -e 's/originaltext/newtext/g'

For example, let's say I have a Makefile for a program called game, which simulates Conway's Game of Life:

.PHONY: all run clean

all: game

game: game.o
        $(CC) $(CFLAGS) -o game game.o $(LDFLAGS)

run: game
        ./game

clean:
        $(RM) *~
        $(RM) *.o
        $(RM) game

The name game isn't very descriptive, so I might choose to rename it life. Renaming the game.c source file to life.c is easy enough, but now I need to modify the Makefile to use the new name. I can use sed to change every occurrence of game to life:

$ sed -e 's/game/life/g' Makefile
.PHONY: all run clean

all: life

life: life.o
        $(CC) $(CFLAGS) -o life life.o $(LDFLAGS)

run: life
        ./life

clean:
        $(RM) *~
        $(RM) *.o
        $(RM) life

This prints the sed output to the screen, which is a good way to check if the text replacement will do what you want. To make these changes to the Makefile, first, make a backup of the file, then run sed and save the output to the original filename:

$ cp Makefile Makefile.old
$ sed -e 's/game/life/g' Makefile.old > Makefile

If you are confident that your changes are exactly what you want, use the -i or --in-place option to edit the file in place. However, I recommend adding a backup filename suffix like --in-place=.old to save a copy of the original file in case you need to restore it later. It looks like this:

$ sed --in-place=.old -e 's/game/life/g' Makefile
$ ls Makefile*
Makefile  Makefile.old

More Linux resources Linux commands cheat sheet Advanced Linux commands cheat sheet Free online course: RHEL technical overview Linux networking cheat sheet SELinux cheat sheet Linux common commands cheat sheet What are Linux containers? Our latest Linux articles Quoting files with sed on Linux

You can use other features of regular expressions to match specific instances of text. For example, you might need to replace text that occurs at the start of a line. With sed, you can match the beginning of a line with ^, the caret character.

One way I use "start of line" in replacing text is when I need to quote a file in an email. Let's say I want to share my Makefile in an email, but I don't want to include it as a file attachment. Instead, I prefer to "quote" the file in the body of an email, using > before each line. I can use the following sed command to print out an edited version to my terminal, which I can copy and paste into a new email:

$ sed -e 's/^/>/' Makefile
>.PHONY: all run clean
>
>all: life
>
>life: life.o
>       $(CC) $(CFLAGS) -o life life.o $(LDFLAGS)
>
>run: life
>       ./life
>
>clean:
>       $(RM) *~
>       $(RM) *.o
>       $(RM) life

The s/^/>/ regular expression matches the start of each line (^) and places a > there. Effectively, this starts each line with the > symbol.

The tabs might not show up correctly in an email, but I can replace all tabs in the Makefile with a few spaces by adding another regular expression:

$ sed -e 's/^/>/' -e 's/\t/  /g' Makefile
>.PHONY: all run clean
>
>all: life
>
>life: life.o
>  $(CC) $(CFLAGS) -o life life.o $(LDFLAGS)
>
>run: life
>  ./life
>
>clean:
>  $(RM) *~
>  $(RM) *.o
>  $(RM) life

The \t indicates a literal tab, so s/\t/ /g tells sed to replace all tabs in the input with two spaces in the output.

If you need to apply lots of edits to files, you can save your -e commands in a file and use -f to tell sed to use that file as a "script." This approach is especially useful if you need to make the same edits frequently. I might have prepared the Makefile for quoting in email using a script file called quotemail.sed:

$ cat quotemail.sed
s/^/>/
s/\t/  /g
$ sed -f quotemail.sed Makefile
>.PHONY: all run clean
>
>all: life
>
>life: life.o
>  $(CC) $(CFLAGS) -o life life.o $(LDFLAGS)
>
>run: life
>  ./life
>
>clean:
>  $(RM) *~
>  $(RM) *.o
>  $(RM) lifeLearn to work with sed on Linux

sed is a great tool to keep in your Linux command-line toolkit. Explore the sed manual page and learn more about how to use it. Type man sed at the command line to get complete documentation about the different command line options and how to use sed to process text files.

Here are some tips and tricks to automating file edits from the Linux command line.

Image by:

Opensource.com

Linux What to read next This work is licensed under a Creative Commons Attribution-Share Alike 4.0 International License. Register or Login to post a comment.

Secure Boot Disabled? GNOME Will Soon Warn You About it!  It's FOSS News

During the month of June the Steam on Linux usage hit a multi-year high point of 1.18% while for July there is another tick upwards thanks to the continued interest in Linux gaming around the Steam Deck...

Steam For Linux In July Shows A 1.23% Marketshare, AMD CPUs Now More Common Than Intel On Linux  Phoronix

DECnet as a set of networking protocols from Digital Equipment Corporation (DEC) that date back to 1975 are expected to be finally removed from the Linux kernel. The DECnet protocols have long been obsolete, the Linux kernel implementation has been orphaned for more than one decade, and is code that belongs more in a history museum than the mainline kernel...

How to create a Linux virtual machine with VirtualBox  ZDNet

How to install Android Studio on an ARM-powered Chromebook  Chrome Unboxed

IO_uring continues to be one of the greatest Linux kernel innovations in recent years and with the in-development Linux 6.0 kernel is getting even better along with some nice block updates and other storage-related enhancements...

This GNOME Extension Brings ‘Material You’ Vibes to Linux Desktops  OMG! Ubuntu!

Linux Mint 21 is now available  Ghacks

Ingo Molnar today submitted the main set of kernel scheduler updates for the in-development Linux 6.0 (nee 5.20). The scheduler updates contain some notable changes that will be interesting to benchmark in the days ahead...

Sven Peter who has worked a lot on various aspects of Apple Silicon enablement for Linux today posted the patches enabling Apple Bluetooth driver support for Apple Silicon M1/M2 hardware and also for some Apple x86 Macs...

Linux Driver Posted Enabling Bluetooth Support For Apple M1/M2, Some x86 Macs  Phoronix

Stealth-action game Republique is now FREE and Steam Deck Verified  GamingOnLinux