[SOLVED] sed simple syntax question

[majpooper]

I have taken several of the tweaks recommended by Pjotr at his web site and put them in a script. The line below works fine, however for readability I would rather it be split into two or three lines. I have researched sed a bit and have tried a million way using the back slash but still cannot split the line and get it to work. It will work the way it is but I would rather it be in more than one line in the script.

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sudo sed -i 's/GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"/GRUB_CMDLINE_LINUX_DEFAULT="quiet splash zswap.enabled=1 zswap.zpool=z3fold zswap.compressor=lz4"/' /etc/default/grub

[AwesomeOpossum74]

How about:

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sudo sed -i s/\
'GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"'/\
'GRUB_CMDLINE_LINUX_DEFAULT="quiet splash zswap.enabled=1 zswap.zpool=z3fold zswap.compressor=lz4"'/\
 /etc/default/grub

I recommend you verify it works on a test file before running it on your working grub file.

[majpooper]

How about:

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sudo sed -i s/\
'GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"'/\
'GRUB_CMDLINE_LINUX_DEFAULT="quiet splash zswap.enabled=1 zswap.zpool=z3fold zswap.compressor=lz4"'/\
 /etc/default/grub

I recommend you verify it works on a test file before running it on your working grub file.

THX much - but one thing I am confused about is:
THIS: the " and the ' inside the / this works for multi line

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compressor=lz4"'/\

AND THIS: The " inside the / and the ' outside this works for a single line

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compressor=lz4"/' /etc/default/grub

The syntax does not seem intuitive I think I get the purpose of the double quotes, but not the single quotes.
I appreciate the help. I have some work to do to try an understand the sed syntax better.

[AwesomeOpossum74]

Normally things inside double quotes would be interpreted, like if you had a $variable. Stuff inside single quotes don't get interpreted, and are passed as is. Since the double quotes are inside the single quotes, the single quotes take precedence, and the double quotes will not be interpreted. Probably a long-winded and confusing explanation. Sorry about that.

Not actually testing this myself, but since the sed delimiter is slash (/), you could probably dispense with the single quotes, unless you later add slashes to the values.

Edit: How about this explanation: The single quotes force the double quotes to be interpreted as part of the string, rather than special characters to be functionally interpreted.

[majpooper]

Normally things inside double quotes would be interpreted, like if you had a $variable. Stuff inside single quotes don't get interpreted, and are passed as is. Since the double quotes are inside the single quotes, the single quotes take precedence, and the double quotes will not be interpreted. Probably a long-winded and confusing explanation. Sorry about that.

Not actually testing this myself, but since the sed delimiter is slash (/), you could probably dispense with the single quotes, unless you later add slashes to the values.

Edit: How about this explanation: The single quotes force the double quotes to be interpreted as part of the string, rather than special characters to be functionally interpreted.

THX - appreciate the explanation - not long winded at all and helpful

[LittleScriptMan]

since the sed delimiter is slash (/)

That is not mandatory. In this topic viewtopic.php?f=213&t=365559, I submitted this command :

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find $CustDir -name '*.cust' -exec sed -i 's|home/'$PrevUser'|home/'$USER'|g' {} +

where the delimiter was the pipe.

In his valuable help answer, rene answered with :

Using s,,,g rather than your s|||g only as a (strong) personal preference...

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sed -i "s,/home/[^/]\+/,/home/$USER/,g" "$CustDir"/*.cust

using the comma as a delimiter.

So, you can use other delimiters when it helps being more readable (the pipe and the comma prevented confusion with the delimiter slash and the slashes included in paths). Of course, you can keep on using slashes even when dealing with paths if the command is set to take the difference in account.

[majpooper]

So, you can use other delimiters when it helps being more readable (the pipe and the comma prevented confusion with the delimiter slash and the slashes included in paths). Of course, you can keep on using slashes even when dealing with paths if the command is set to take the difference in account.

THX - I think I am beginning to catch on . . . . albeit slowly.
I have been looking over a sed tutorial online - it shows basics commands and uses delimiters but really does not explain them in terms hierarchy if there is one . . . . or do you just use them interchangeably to suit one's preference and readability. I guess I will just have to experiment.

BTW - when I started delving into java script about a year ago I haven't learned much but I sure have broken a lot of stuff. Good thing I was a Business major (Industrial Relations) and not Computer Science, I would have never made it past my Freshman year.

[LittleScriptMan]

I have been looking over a sed tutorial online - it shows basics commands and uses delimiters but really does not explain them in terms hierarchy if there is one . . . . or do you just use them interchangeably to suit one's preference and readability. I guess I will just have to experiment.

There is no hierarchy. You can use any except the backslash and the newline, even A,z, 4, £. Of course, the goal should still be better readability. Probably special characters with accents (french), tildes (spanish) or diaresis (swedish) would be problematic too. Never tried. Either the usual / or the pipe when already using slashes in the search or replace expressions worked fine for me, even if the comma may seem more different from the slash than the pipe with is somewhat a vertical slash.

About tutorials, I work on the Baeldung site. Here are their links about sed hoping they may provide some help :
https://www.baeldung.com/linux/grep-sed-awk-differences
https://www.baeldung.com/linux/sed-editor
https://www.baeldung.com/linux/sed-subs ... -variables
https://www.baeldung.com/linux/sed-with-string
https://www.baeldung.com/linux/sed-repl ... ine-string
https://www.baeldung.com/linux/sed-awk-return-value