Interview › Scripting (Bash, Groovy)

What is the difference between sed -i and sed without -i? [Advanced]

Answer

sed without -i streams the modified result to stdout and leaves the source file unchanged. sed -i edits the file in place, optionally creating a backup depending on the argument used.

Technical explanation

Without -i is safer for previewing, pipelines, and redirection to a new file.

With -i is convenient but can be risky if the expression is wrong or portability across GNU/BSD sed matters.

In automated scripts, prefer creating a backup or using a temp file plus atomic mv for critical files.

Hands-on example

# Safe preview

sed 's/replicas: 1/replicas: 3/' deploy.yaml > deploy.new.yaml

mv deploy.new.yaml deploy.yaml
# GNU sed in-place with backup
sed -i.bak 's/replicas: 1/replicas: 3/' deploy.yaml

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