Is there a grep equivalent for find's -print0 and xargs's -0 switches?

问题

I often want to write commands like this (in zsh, if it's relevant):

find <somebasedirectory> | \
    grep stringinfilenamesIwant | \
    grep -v stringinfilesnamesIdont | \
    xargs dosomecommand

(or more complex combinations of greps)

In recent years find has added the -print0 switch, and xargs has added -0, which allow handling of files with spaces in the name in an elegant way by null-terminating filenames instead, allowing for this:

find <somebasedirectory> -print0 | xargs -0 dosomecommand

However, grep (at least the version I have, GNU grep 2.10 on Ubuntu), doesn't seem to have an equivalent to consume and generate null-terminated lines; it has --null, but that only seems related to using -l to output names when searching in files directly with grep.

Is there an equivalent option or combination of options I can use with grep? Alternatively, is there an easy and elegant way to express my pipe of commands simply using find's -regex, or perhaps Perl?

回答1:

Use GNU Grep's `--null` Flag

According to the GNU Grep documentation, you can use Output Line Prefix Control to handle ASCII NUL characters the same way as find and xargs.

-Z
--null
Output a zero byte (the ASCII NUL character) instead of the character that normally follows a file name. For example, ‘grep -lZ’ outputs a zero byte after each file name instead of the usual newline. This option makes the output unambiguous, even in the presence of file names containing unusual characters like newlines. This option can be used with commands like ‘find -print0’, ‘perl -0’, ‘sort -z’, and ‘xargs -0’ to process arbitrary file names, even those that contain newline characters.

Use `tr` from GNU Coreutils

As the OP correctly points out, this flag is most useful when handling filenames on input or output. In order to actually convert grep output to use NUL characters as line endings, you'd need to use a tool like sed or tr to transform each line of output. For example:

find /etc/passwd -print0 |
    xargs -0 egrep -Z 'root|www' |
    tr "\n" "\0" |
    xargs -0 -n1

This pipeline will use NULs to separate filenames from find, and then convert newlines to NULs in the strings returned by egrep. This will pass NUL-terminated strings to the next command in the pipeline, which in this case is just xargs turning the output back into normal strings, but it could be anything you want.

回答2:

As you are already using GNU find you can use its internal regular expression pattern matching capabilities instead of these grep, eg:

find <somebasedirectory> -regex ".*stringinfilenamesIwant.*" ! -regex ".*stringinfilesnamesIdont.*" -exec dosomecommand {} +

回答3:

The newest version of the GNU grep source can now use -z/--null to separate the output by null characters, while it previously only worked in conjunction with -l:

http://git.savannah.gnu.org/cgit/grep.git/commit/?id=cce2fd5520bba35cf9b264de2f1b6131304f19d2

This means that your issue is solved automatically when using the newest version.

回答4:

Instead of using a pipe, you can use find's -exec with the + terminator. To chain multiple commands together, you can spawn a shell in -exec.

find ./ -type f -exec bash -c 'grep "$@" | grep -v something | xargs dosomething' -- {} +

回答5:

Use

find <somebasedirectory> -print0 | \
 grep -z stringinfilenamesIwant | \
 grep -zv stringinfilesnamesIdont | \
 xargs -0 dosomecommand

However, the pattern may not contain newline, see bug report.

回答6:

find <somebasedirectory> -print0 | xargs -0 -I % grep something '%'

来源：https://stackoverflow.com/questions/15976570/is-there-a-grep-equivalent-for-finds-print0-and-xargss-0-switches

标签

bash

unix

grep

find

xargs