sed

Replace word

Using a string literal.

$ echo 'football' | sed 's/foo/bar/g'
bartball
$ echo 'football' | sed 's/foo/bar/g'
tball

Using a variable.

$ x='football'
$ echo $x | sed 's/foo/bar/g'
bartball

Replace inline in file with backup flag

You can optionally provide an extension - typically .bak. This will create a backup of the file before overwriting it.

Here assume pattern is like 's/foo/bar/g' and the PATH could be * or a filename.

This will work the same on Linux and macOS:

$ sed -i'' 's/foo/bar/g' file.txt

Note platform-specific usage below.

Linux

Using GNU Linux version.

Examples:

$ # No backup.
$ sed PATTERN PATH
$ sed -i PATTERN PATH
$ sed -i '' PATTERN PATH

$ # Backup as .bak files.
$ sed -i=.bak PATTERN PATH

A backup is made if you supply a suffix - but you must not leave a gap between the flag and the suffix.

-i[SUFFIX], --in-place[=SUFFIX]

        edit files in place (makes backup if SUFFIX supplied)

macOS

Using BSD macOS version.

You must provide an argument for inline. Even if it’s an empty string for no backup.

Good examples:

$ # No backup.
$ sed -i '' PATTERN PATH

$ # Backup as .bak files.
$ sed -i '.bak' PATTERN PATH

Note that a space is required and not use of equals sign. Using -i='' will get the equals sign interpreted literally.

Leaving out a space or leaving out the argument will give an error.

$ sed -i'' PATTERN PATH
$ sed -i PATTERN PATH

Or you should install and alias the GNU sed on macOS as sed.