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I am using the following to search a directory recursively for specific string and replace it with another:

grep -rl oldstr path | xargs sed -i 's/oldstr/newstr/g'

This works okay. The only problem is that if the string doesn't exist then sed fails because it doesn't get any arguments. This is a problem for me since i'm running this automatically with ANT and the build fails since sed fails.

Is there a way to make it fail-proof in case the string is not found?

I'm interested in a one line simple solution I can use (not necessarily with grep or sed but with common unix commands like these).

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  • the reason i want to keep it as simple as possible is because my script connects to a remote server and runs this line with SSH. if i would use a shell script for this, i would have to copy the shell script to the server before and then run it there. i'm trying to avoid it and keep it simple. thanks. Commented May 30, 2011 at 16:14
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    superuser.com/questions/257250/… Commented May 30, 2011 at 16:47
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    Coming here from Google, I was looking for the exact string given in the question! (I didn't have the problem the OP was suffering from) Commented Nov 17, 2015 at 12:34

8 Answers 8

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83

You can use find and -exec directly into sed rather than first locating oldstr with grep. It's maybe a bit less efficient, but that might not be important. This way, the sed replacement is executed over all files listed by find, but if oldstr isn't there it obviously won't operate on it.

find /path -type f -exec sed -i 's/oldstr/newstr/g' {} \;
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9 Comments

@Vlad: It is, because you're running a separate sed for each file instead of letting xargs batch them. That said, unless you're talking about several thousand tiny files, you're unlikely to notice a difference.
@geekosaur: Oh, right.. I haven't thought about a number of execs shell should make. Good point!
My problem with this: the timestamp of every file will get reset to "right now" as if they were all "touched", even if no edits occurred in the file.
I've seen this "Hello world" example of using find all over the place, but nothing that constrains it from running sed on every file, including binaries. I have yet to find a working example with pipes, and I've tried a number of ways to hack the simplistic version of very limited utility.
@JerryMiller you can of course limit find to specific filename patterns, which is what I often do: find -name "*.c" -o -name "*.h" -type f -exec sed... would modify all the .c and .h files for example... To exclude binary files, it can get more complicated: unix.stackexchange.com/questions/46276/…
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19

Your solution is ok. only try it in this way:

files=$(grep -rl oldstr path) && echo $files | xargs sed....

so execute the xargs only when grep return 0, e.g. when found the string in some files.

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2 Comments

That is a nice underestimated solution! This is what I needed to execute sed over a list of files output of grep, and avoid the error: "can't read .... No such file or directory". Thanks for your answer!
Agree with @Leopoldo. This looks like the most Posixy and portable (for OS like Solaris) and the one with the least side effects (not touching every file mtime, etc). files=$(grep -rl oldstr path | cut -f 1 -d ':' | sort | uniq) should build a smaller list where the files are listed once.
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I have taken Vlad's idea and changed it a little bit. Instead of 

grep -rl oldstr path | xargs sed -i 's/oldstr/newstr/g' /dev/null

Which yields 

sed: couldn't edit /dev/null: not a regular file

I'm doing in 3 different connections to the remote server

touch deleteme
grep -rl oldstr path | xargs sed -i 's/oldstr/newstr/g' ./deleteme
rm deleteme

Although this is less elegant and requires 2 more connections to the server (maybe there's a way to do it all in one line) it does the job efficiently as well

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1 Comment

And this script save my life!
8

Standard xargs has no good way to do it; you're better off using find -exec as someone else suggested, or wrap the sed in a script which does nothing if there are no arguments. GNU xargs has the --no-run-if-empty option, and BSD / OS X xargs has the -L option which looks like it should do something similar.

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3 Comments

thanks, i tried to use --no-run-if-empty but it still returns nonzero code (returns 1) and that would also trigger a build fail for me. how generic and common is find command ?
find -exec goes back to 7th Research Edition UNIX; it should work anywhere that has find installed.
+1 I'm surprised the xargs -r fix is not mentioned in more answers. For this limited use case, it's simple and sufficient.
4

I think that without using -exec you can simply provide /dev/null as at least one argument in case nothing is found:

grep -rl oldstr path | xargs sed -i 's/oldstr/newstr/g' /dev/null
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4 Comments

could be a very neat workaround. sadly i get sed: couldn't edit /dev/null: not a regular file :)
@michael: Turns out - running anything like this will actually crash the shell because of too many arguments... See superuser.com/questions/257250/…
there are a lot of files in my directory but only few of them contain the string i want to change. so i am not so worried about too many arguments to sed.
@michael: The solution listed there with 10 votes should do the job.
1

My use case was I wanted to replace foo:/Drive_Letter with foo:/bar/baz/xyz In my case I was able to do it with the following code. I was in the same directory location where there were bulk of files.

find . -name "*.library" -print0 | xargs -0 sed -i '' -e 's/foo:\/Drive_Letter:/foo:\/bar\/baz\/xyz/g'

hope that helped.

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0

Not sure if this will be helpful but you can use this with a remote server like the example below

ssh example.server.com "find /DIR_NAME -type f -name "FILES_LOOKING_FOR" -exec sed -i 's/LOOKINGFOR/withThisString/g' {} ;"

replace the example.server.com with your server replace DIR_NAME with your directory/file locations replace FILES_LOOKING_FOR with files you are looking for replace LOOKINGFOR with what you are looking for replace withThisString with what your want to be replaced in the file

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-1

If you are to replace a fixed string or some pattern, I would also like to add the bash builtin pattern string replacement variable substitution construct. Instead of describing it myself, I am quoting the section from the bash manual:

${parameter/pattern/string}

The pattern is expanded to produce a pattern just as in pathname expansion. parameter is expanded and the longest match of pattern against its value is replaced with string. If pattern begins with /, all matches of pattern are replaced with string. Normally only the first match is replaced. If pattern begins with #, it must match at the beginning of the expanded value of parameter. If pattern begins with %, it must match at the end of the expanded value of parameter. If string is null, matches of pattern are deleted and the / following pattern may be omitted. If parameter is @ or *, the substitution operation is applied to each positional parameter in turn, and the expansion is the resultant list. If parameter is an array variable subscripted with @ or *, the substitution operation is applied to each member of the array in turn, and the expansion is the resultant list.

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