Sam Stites

Writing a small bootstrap 3 downgrader in sed

04 Sept 2014 - Redwood City, CA

Some notes on sed: always use -E for the more ‘standard’ regex always use single quotes for the regex so that you don’t have to escape metacharacters sed doesnt allow for non capture groups you can execute a script with -e (not nessecary for a regex) chop up your regexs into smaller ones and use -e to seperate out regexs by ;s you can use -i to change a file on the fly. use .bak for a backup as you write or . for none


sed -E \
-e 's/(col-sm-)|(col-md-)([0-9]+)/span\3/g;s/span([0-9]+) span[0-9]+/span\1/g' \
-i.bak <template>.html

Running this agains multiple files requires you to find all files:

find *.html -type f -print0

-print0 always evaluates to true and prints to stout followed by an ASCII NUL character (\0).

then pipe each result into xargs - -0 takes \0 as a seperator, -n is the number of arguments the utility takes:

xargs -0 -n 1 < <utility> <utility args> >

Putting this all together:

find *.html -type f -print0 | \
xargs -0 -n 1 \
sed -E -i.bak \
-e 's/(col-sm-)|(col-md-)([0-9]+)/span\3/g;s/span([0-9]+) span[0-9]+/span\1/g'

And we’ve created our bootstrap 3 downgrader!