sed

Replace a word in a file or in a pipe, every time it appears, or right inside the file with sed -i.

>_ Try it: a simulated Linux, right herenothing runs on your computer

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Examples

sed "s/3000/8080/" app.conf change the port (on screen only)
sed "s/example/dockerlinux/g" links.txt every match on each line
sed "s|http://|https://|" links.txt paths and URLs: use | instead of /
sed -i "s/debug=true/debug=false/" app.conf now really change the file
cat app.conf the file has changed
echo "hello world" | sed "s/world/Linux/" it edits a pipe too

How it works

sed "s/OLD/NEW/" FILE prints the file with the first OLD on each line replaced by NEW. The file itself is not changed — you see the result.

Add g at the end to replace every match on a line, and -i to write the change into the file (in place). Check the output first, then run it again with -i.

Syntax

sed [-i] "s/OLD/NEW/[g]" [FILE]...

Options

Option	What it does
`s/OLD/NEW/`	replace the first OLD on each line with NEW
`g`	global: every match on the line, not just the first
`-i`	in place: save the change into the file
`s\|A\|B\|`	any character can separate the parts: handy when the text has slashes

Good to know

Without -i sed never touches the file: try your replacement safely first, then add -i.
OLD is a pattern: a dot means "any character". To replace a literal dot, write \..