Using sed regex for string replacement

Question

I am trying to replace a string in the config file. I would like to run something like this:

OS

(docker image php:8.1-apache-buster)

Debian GNU/Linux 10 (buster)

sed (GNU sed) 4.7 Packaged by Debian

Possible inputs:

post_max_size = 4M
post_max_size = 24M
post_max_size = 248M
...

Example output (any user given value):

post_max_size = 128M

Example cmd:

sed -i 's/(post_max_size = ([0-9]{1,})M/post_max_size = 128M/g' /usr/local/etc/php/php.ini

Joining regex with strings does not work here.

It works when I run string replace without any regex

sed -i 's/post_max_size = 8M/post_max_size = 128M/g' /usr/local/etc/php/php.ini

This works only if the value of the post_max_size is set exactly to 2M. I would like to be able to make a change with regex regardless of the value set.

I searched the Internet and sed cmd docs but did not find anything which fits my use case.

Please add sample input (no descriptions, no images, no links) and your desired output for that sample input to your question (no comment). — Cyrus
– Cyrus, Commented Nov 13, 2022 at 9:36
Try sed -i -E '/post_max_size = /s/([0-9]{1,})M/128M/' /usr/local/etc/php/php.ini — fpmurphy
– fpmurphy, Commented Nov 13, 2022 at 10:31

C-nan · Accepted Answer · 2022-11-13 10:29:09Z

2

The following should work:

sed -i 's/^post_max_size = .*/post_max_size = 128M/g' /usr/local/etc/php/php.ini

answered Nov 13, 2022 at 10:29

C-nan

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Comments

The fourth bird · Accepted Answer · 2022-11-14 16:38:32Z

1

You can match optional spaces with [[:space:]]*, the -E for extended-regexp and use group 1 noted as \1 followed by your replacement like \1128M

sed -E -i 's/(post_max_size[[:space:]]*=[[:space:]]*)[0-9]+M/\1128M/g' /usr/local/etc/php/php.ini

edited Nov 14, 2022 at 16:38

answered Nov 13, 2022 at 11:22

The fourth bird

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7 Comments

DevWL Over a year ago

There is something missing here. I have tried this and similar commands, but it does not trigger string replacement. @C-nan cmd worked.

The fourth bird Over a year ago

@DevWL What is your os?

DevWL Over a year ago

its a dockeriesd container of php & Apache image "Debian GNU/Linux 10 (buster)"

DevWL Over a year ago

@fpmmurphy command also worked: sed -i -E '/post_max_size = /s/([0-9]{1,})M/128M/' /usr/local/etc/php/php.ini

DevWL Over a year ago

Yes this works also in my use case, Thanks

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