FAQ: Redirection - sed

This community-built FAQ covers the “sed” exercise from the lesson “Redirection”.

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This exercise can be found in the following Codecademy content:

Web Development

Learn the Command Line

FAQs on the exercise sed

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When I followed the steps to substitute “snow” for “rain” in this exercise, it printed the changes to the terminal each time, but did not actually change the document forests.txt. So when I did the final step and used “cat forests.txt”, none of the instances of “snow” had been replaced with “rain”.

How do I make the substitutions permanent in forests.txt?

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Welcome back to the forums!

You can use the -i option to edit a file permanently.

See here for more information.

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Thank you! That is helpful.

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is it necessary to enclose expressions in apostrophe ‘’ ?

because in lesson expressions work fine without them

Quotes are very important in certain bash expressions; the following seems to cover some info (or have a web search for the same terms if you prefer a different guide):
https://wiki.bash-hackers.org/syntax/quoting

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Hi! Although I try to replace the first ‘snow’ only with sed ‘s/snow/rain/’ forests.txt, it replaces the part of the text:
sed ‘s/snow/rain/’ forests.txt

Could you please explain the reason?

I’m not certian what you mean, sed works linewise and you requested that snow be replaced with rain which seems to be what occurred. The fnal /g flag would replace all instances of the substring within a given line such that the final line would be Pacific Temperature: rainforest rainforest from the original Pacific Temperature: snowforest snowforest

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Ah, I got it wrong first. I thought only the first snow should be replaced in the first line The Amazon rainforest. I got it now, thank you!

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