Linux Shell Scripting Cookbook - Third Edition

Performing replacement directly in the file

When a filename is passed to sed, it usually prints to stdout. The -I option will cause sed to modify the contents of the file in place:

    $ sed 's/PATTERN/replacement/' -i filename

For example, replace all three-digit numbers with another specified number in a file, as follows:

    $ cat sed_data.txt
    11 abc 111 this 9 file contains 111 11 88 numbers 0000

    $ sed -i 's/\b[0-9]\{3\}\b/NUMBER/g' sed_data.txt
    $ cat sed_data.txt
    11 abc NUMBER this 9 file contains NUMBER 11 88 numbers 0000

The preceding one-liner replaces three-digit numbers only. \b[0-9]\{3\}\b is the regular expression used to match three-digit numbers. [0-9] is the range of digits from 0 to 9. The {3} string defines the count of digits. ...