Shell Programming and Scripting

Note that with either find ... -exec ... + or with xargs, if only one matching file is found or if there are enough matching files to invoke grep multiple times and the last invocation only passes one filename to grep, the filename will not be printed along with the matching line. To protect against this rare case, add another file operand that you know will never match your pattern:

Code:

find . -name '*.c' -exec grep -E '&[[:alpha:]]+\[[0-9]+\]' /dev/null {} +

Does any of your code contain array variables with underscores or digits in their names? If so, maybe you want:

Code:

find . -name '*.c' -exec grep -E '&[_[:alpha:]][_[:alnum:]]*\[[0-9]+\]' /dev/null {} +

Hi Don, originally I wanted to expand my post with something similar (using -H if the user's grep supports it). With /dev/null option I worried that if the ARG_MAX would be reached with that xargs or + option, ARG_MAX might become exceeded when those arguments are fed to grep together with /dev/null. What are your thoughts on this?


I also did a small test with only one file and I found this, using OSX:

Code:

$ cat testdir/infile1
x
$ grep x ./testdir/infile1 
x
$ find . -name 'i*1' | xargs grep 'x'
./testdir/infile1:x
$ find . -name 'i*1' -exec grep 'x' {} +
./testdir/infile1:x
$ find . -name 'i*1' -exec grep 'x' {} \;
x

So it would seem that somehow the /dev/null precaution is only necessary when using \;

--EDIT--
Nevermind about that last bit, it seems this is not common behaviour , on other OS it does not print the file name, so this appears to be implementation specific.

According to the standards, grep is not allowed to print the name of the matched file unless two or more file operands are specified; and is required to print the name of the matched file if two or more file operands are specified. (The standards do not specify the -H option, but that is an allowed extension.)

find ... -exec ... + and xargs are required by the standards to limit the command line length such that when the command is invoked, the combined argument and environment lists shall not exceed {ARG_MAX} bytes. Of course, if the environment, fixed arguments, and one pathname exceed {ARG_MAX}; neither find nor xargs will be able to invoke any commands. And, with some options, xargs is also constrained by {LINE_MAX}.