How to replace a string in a file? — First published in fullweb.io issue #84

how-to-replace-a-string-in-a-file.md

How to replace a string in a file?

The simplest way to proceed is to use sed. It‘s available both on Mac and Linux. Here is the gist of it:

sed -i 's/old/new/g' file.txt

Here we’re replacing old with new. The -i option will replace the string inplace. The /g flag will replace every occurrences in the file.

@nepsilon Doesn't work for me on macOS:

[02:01:12] /tmp
 » which sed
/usr/bin/sed
[02:01:15] /tmp
 » echo "old" > file.txt
[02:01:18] /tmp
 » sed -i 's/old/new/g' file.txt
sed: 1: "file.txt": invalid command code f

This does, but creates that backup file (which I think -i may expect as an argument):

[02:01:12] /tmp
 » which sed
/usr/bin/sed
[02:01:15] /tmp
 » echo "old" > file.txt
[02:02:15] /tmp
 » sed -i .bak 's/old/new/g' file.txt
[02:02:22] /tmp
 » cat file.txt
new
[02:02:30] /tmp
 » cat file.txt.bak
old

@josephgrossberg Good catch! My example seems to work only with GNU sed, not the BSD sed which is pre-installed on Mac.

The BSD sed needs a value to its -i option, to specify the extension of the backup file.