April 23, 2023

Substitute one word (or a pattern) for another through a whole file from the command line

You can substitute one word for another through a whole file by running:

$ sed s/oldword/newword/g inputfile > outputfile

What’s happening in this command?

First you tell the terminal to run sed, the name of the programme (more info below).

Next you tell sed that you want to run a replacement of oldword’ by newword’.

We start with s, which stands for substitute.

The /s are just separators.

The g tells sed to apply the substitution on all occurrences of oldword’ throughout the file. If you omit g, sed will only perform the substitution on the first encounter of oldword’, leaving other oldword’ unchanged.

inputfile is the file which you have with oldword’.

outputfile will be a file created with newword’, once the substitution procedure is completed.

> is what is called a redirection, that says from an input file to an output file.

What is sed?

Sed is a stream editor, that is a programme to perform basic text transformations on an input stream, a file for example. There is a lot more you can do with sed; if you have a repetitive text editing tasks to run, sed might be able to help you. For example, you can delete lines that contains a specific keyword, or add a line to a file (e.g. add an item to a to-do list).

You can run $ man sed or $ info sed to learn more or see some examples.

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