Question

So essentially I want to understand why this command- sent to terminal as a one-liner doesn’t work as intended. It runs for several minutes but my test files containing “teststring1” don’t get replaced. Please without radically changing the syntax or asking why I am doing this from root, can anyone identify the reason why it doesn’t?

cd /tmp;find / -maxdepth 3 -type f -print0 | xargs -0 sed -i 's/teststring1/itworked!/gI'

Answer 1

Citate from man sed:

If  no  -e,  --expression, -f, or --file option is given, then the first non-option argument is taken as the sed script to interpret.  All remaining arguments are names of input files; if no input files are specified, then the standard input is read.

s/regular expression/replacement/flags  
The value of flags in the substitute function is zero or more of the following:
- N       Make the substitution only for the N'th occurrence of the regular expression in the pattern space.
- g       Make the substitution for all non-overlapping matches of the regular expression, not just the first one.
- p       Write the pattern space to standard output if a replacement was made.  If the replacement string is identical to that which it replaces, it is still considered to have been a replacement.
- w file  Append the pattern space to file if a replacement was made.  If the replacement string is identical to that which it replaces, it is still considered to have been a replacement.

So find / -maxdepth 3 -type f -print0 | xargs -0 sed -e 's/[tT][eE][sS][tT][sS][tT][rR][iI][nN][gG]1/itworked!/g' -i will work as you want.

If you do not like ugly pattern for case insensitive matches, you can use perl instead of sed: find / -maxdepth 3 -type f -print0 | xargs -0 perl -pe 's/teststring1/itworked!/ig' -i