Not sure if this is possible...
I'm trying to write a terminal command (linux) that would find all video files with a specific extension and then convert them using HandBrakeCLI
I have the first half of that down:
find . -type f -name "*.avi*" -exec
And I have a working HandBrakeCLI command:
HandBrakeCLI -i file.mkv -o file2.mkv -e x265 --vfr -q 20 --all-audio --all-subtitles
What I have been unable to figure out is how to insert the file name/path for the files found in the find into the file.mkv and then output the converted file with the same file name but in an mkv format.
Is it possible to do this in one line or do I need to break this out in a bash script?
As a one-liner, try something like:
find . -type f -name "*.avi" -print0 | perl -pe 's/\.avi\0/\0/g' | xargs -0 -I% HandBrakeCLI -i %.avi -o %.mkv -e x265 --vfr -q 20 --all-audio --all-subtitles
-print0 option in find prints the filename on the standard output, followed by a null character.
The following perl snippet removes the .avi extention to supply the basename to xargs.
-I% option in xargs replaces "%" with names read from standard input.
I'm doing a find and locating several executables that I want to run with -v. I tried something like this:
find somefilters | xargs -I % % -v
Unfortuntely, xargs seems to require that the "utility" be a fixed binary rather than a binary provided by stdin. Does anyone have a recipe for doing this command line magic?
Use the -exec primary:
find ... -exec '{}' -v \;
Yet another way around this - use xargs to write a shell script for you:
find somefilters | xargs -n 1 -I % echo % -v | ${SHELL}
That won't work out so well if any of the programs require interactivity, but if the -v option is just to spit out the version numbers or something (one common meaning, the other being a verbose flag), it should work fine.
So after a lot of searching and trying to interpret others' questions and answers to my needs, I decided to ask for myself.
I'm trying to take a directory structure full of images and place all the images (regardless of extension) in a single folder. In addition to this, I want to be able to remove images matching certain filenames in the process. I have a find command working that outputs all the filepaths for me
find -type f -exec file -i -- {} + | grep -i image | sed 's/\:.*//'
but if I try to use that to copy files, I have trouble with the spaces in the filenames.
cp `find -type f -exec file -i -- {} + | grep -i image | sed 's/\:.*//'` out/
What am I doing wrong, and is there a better way to do this?
With the caveat that it won't work if files have newlines in their names:
find . -type f -exec file -i -- {} + |
awk -vFS=: -vOFS=: '$NF ~ /image/{NF--;printf "%s\0", $0}' |
xargs -0 cp -t out/
(Based on answer by Jonathan Leffler and subsequent comments discussion with him and #devnull.)
The find command works well if none of the file names contain any newlines. Within broad limits, the grep command works OK under the same circumstances. The sed command works fine as long as there are no colons in the file names. However, given that there are spaces in the names, the use of $(...) (command substitution, also indicated by back-ticks `...`) is a disaster. Unfortunately, xargs isn't readily a part of the solution; it splits on spaces by default. Because you have to run file and grep in the middle, you can't easily use the -print0 option to (GNU) find and the -0 option to (GNU) xargs.
In some respects, it is crude, but in many ways, it is easiest if you write an executable shell script that can be invoked by find:
#!/bin/bash
for file in "$#"
do
if file -i -- "$file" | grep -i -q "$file:.*image"
then cp "$file" out/
fi
done
This is a little painful in that it invokes file and grep separately for each name, but it is reliable. The file command is even safe if the file name contains a newline; the grep is probably not.
If that script is called 'copyimage.sh', then the find command becomes:
find . -type f -exec ./copyimage.sh {} +
And, given the way the grep command is written, the copyimage.sh file won't be copied, even though its name contains the magic word 'image'.
Pipe the results of your find command to
xargs -l --replace cp "{}" out/
Example of how this works for me on Ubuntu 10.04:
atomic#atomic-desktop:~/temp$ ls
img.png img space.png
atomic#atomic-desktop:~/temp$ mkdir out
atomic#atomic-desktop:~/temp$ find -type f -exec file -i \{\} \; | grep -i image | sed 's/\:.*//' | xargs -l --replace cp -v "{}" out/
`./img.png' -> `out/img.png'
`./img space.png' -> `out/img space.png'
atomic#atomic-desktop:~/temp$ ls out
img.png img space.png
atomic#atomic-desktop:~/temp$
I have a bash 'for loop' that does what I want
for i in *.data
do
./prog $i >dir/$i.bck
done
Can I turn this into an xargs construct ?
I've tried something like
ls *.data|xargs -n1 -I FILE ./prog FILE >dir/FILE.bck
But I have problems with the FILE rightside of '>'
thanks
Give this a try (you can use FILE instead of % if you prefer):
find -maxdepth 1 -name '*.data' -print0 | xargs -0 -n1 -I % sh -c './prog % > dir/%.bck'
GNU Parallel http://www.gnu.org/software/parallel/ is designed for this kind of tasks:
ls *.data | parallel ./prog {} '>'dir/{}.bck
IMHO this is more readable than the xargs solution provided.
Watch the intro video to learn more: http://www.youtube.com/watch?v=OpaiGYxkSuQ
How can I make xargs execute the command exactly once for each line of input given?
It's default behavior is to chunk the lines and execute the command once, passing multiple lines to each instance.
From http://en.wikipedia.org/wiki/Xargs:
find /path -type f -print0 | xargs -0 rm
In this example, find feeds the input of xargs with a long list of file names. xargs then splits this list into sublists and calls rm once for every sublist. This is more efficient than this functionally equivalent version:
find /path -type f -exec rm '{}' \;
I know that find has the "exec" flag. I am just quoting an illustrative example from another resource.
The following will only work if you do not have spaces in your input:
xargs -L 1
xargs --max-lines=1 # synonym for the -L option
from the man page:
-L max-lines
Use at most max-lines nonblank input lines per command line.
Trailing blanks cause an input line to be logically continued on
the next input line. Implies -x.
It seems to me all existing answers on this page are wrong, including the one marked as correct. That stems from the fact that the question is ambiguously worded.
Summary: If you want to execute the command "exactly once for each line of input," passing the entire line (without newline) to the command as a single argument, then this is the best UNIX-compatible way to do it:
... | tr '\n' '\0' | xargs -0 -n1 ...
If you are using GNU xargs and don't need to be compatible with all other UNIX's (FreeBSD, Mac OS X, etc.) then you can use the GNU-specific option -d:
... | xargs -d\\n -n1 ...
Now for the long explanation…
There are two issues to take into account when using xargs:
how does it split the input into "arguments"; and
how many arguments to pass the child command at a time.
To test xargs' behavior, we need an utility that shows how many times it's being executed and with how many arguments. I don't know if there is a standard utility to do that, but we can code it quite easily in bash:
#!/bin/bash
echo -n "-> "; for a in "$#"; do echo -n "\"$a\" "; done; echo
Assuming you save it as show in your current directory and make it executable, here is how it works:
$ ./show one two 'three and four'
-> "one" "two" "three and four"
Now, if the original question is really about point 2. above (as I think it is, after reading it a few times over) and it is to be read like this (changes in bold):
How can I make xargs execute the command exactly once for each argument of input given? Its default behavior is to chunk the input into arguments and execute the command as few times as possible, passing multiple arguments to each instance.
then the answer is -n 1.
Let's compare xargs' default behavior, which splits the input around whitespace and calls the command as few times as possible:
$ echo one two 'three and four' | xargs ./show
-> "one" "two" "three" "and" "four"
and its behavior with -n 1:
$ echo one two 'three and four' | xargs -n 1 ./show
-> "one"
-> "two"
-> "three"
-> "and"
-> "four"
If, on the other hand, the original question was about point 1. input splitting and it was to be read like this (many people coming here seem to think that's the case, or are confusing the two issues):
How can I make xargs execute the command with exactly one argument for each line of input given? Its default behavior is to chunk the lines around whitespace.
then the answer is more subtle.
One would think that -L 1 could be of help, but it turns out it doesn't change argument parsing. It only executes the command once for each input line, with as many arguments as were there on that input line:
$ echo $'one\ntwo\nthree and four' | xargs -L 1 ./show
-> "one"
-> "two"
-> "three" "and" "four"
Not only that, but if a line ends with whitespace, it is appended to the next:
$ echo $'one \ntwo\nthree and four' | xargs -L 1 ./show
-> "one" "two"
-> "three" "and" "four"
Clearly, -L is not about changing the way xargs splits the input into arguments.
The only argument that does so in a cross-platform fashion (excluding GNU extensions) is -0, which splits the input around NUL bytes.
Then, it's just a matter of translating newlines to NUL with the help of tr:
$ echo $'one \ntwo\nthree and four' | tr '\n' '\0' | xargs -0 ./show
-> "one " "two" "three and four"
Now the argument parsing looks all right, including the trailing whitespace.
Finally, if you combine this technique with -n 1, you get exactly one command execution per input line, whatever input you have, which may be yet another way to look at the original question (possibly the most intuitive, given the title):
$ echo $'one \ntwo\nthree and four' | tr '\n' '\0' | xargs -0 -n1 ./show
-> "one "
-> "two"
-> "three and four"
As mentioned above, if you are using GNU xargs you can replace the tr with the GNU-specific option -d:
$ echo $'one \ntwo\nthree and four' | xargs -d\\n -n1 ./show
-> "one "
-> "two"
-> "three and four"
If you want to run the command for every line (i.e. result) coming from find, then what do you need the xargs for?
Try:
find path -type f -exec your-command {} \;
where the literal {} gets substituted by the filename and the literal \; is needed for find to know that the custom command ends there.
EDIT:
(after the edit of your question clarifying that you know about -exec)
From man xargs:
-L max-lines
Use at most max-lines nonblank input lines per command line. Trailing
blanks cause an input line to be logically continued on the next input line.
Implies -x.
Note that filenames ending in blanks would cause you trouble if you use xargs:
$ mkdir /tmp/bax; cd /tmp/bax
$ touch a\ b c\ c
$ find . -type f -print | xargs -L1 wc -l
0 ./c
0 ./c
0 total
0 ./b
wc: ./a: No such file or directory
So if you don't care about the -exec option, you better use -print0 and -0:
$ find . -type f -print0 | xargs -0L1 wc -l
0 ./c
0 ./c
0 ./b
0 ./a
How can I make xargs execute the command exactly once for each line of input given?
-L 1 is the simple solution but it does not work if any of the files contain spaces in them. This is a key function of find's -print0 argument – to separate the arguments by '\0' character instead of whitespace. Here's an example:
echo "file with space.txt" | xargs -L 1 ls
ls: file: No such file or directory
ls: with: No such file or directory
ls: space.txt: No such file or directory
A better solution is to use tr to convert newlines to null (\0) characters, and then use the xargs -0 argument. Here's an example:
echo "file with space.txt" | tr '\n' '\0' | xargs -0 ls
file with space.txt
If you then need to limit the number of calls you can use the -n 1 argument to make one call to the program for each input:
echo "file with space.txt" | tr '\n' '\0' | xargs -0 -n 1 ls
This also allows you to filter the output of find before converting the breaks into nulls.
find . -name \*.xml | grep -v /target/ | tr '\n' '\0' | xargs -0 tar -cf xml.tar
These two ways also work, and will work for other commands that are not using find!
xargs -I '{}' rm '{}'
xargs -i rm '{}'
example use case:
find . -name "*.pyc" | xargs -i rm '{}'
will delete all pyc files under this directory even if the pyc files contain spaces.
Another alternative...
find /path -type f | while read ln; do echo "processing $ln"; done
find path -type f | xargs -L1 command
is all you need.
The following command will find all the files (-type f) in /path and then copy them using cp to the current folder. Note the use if -I % to specify a placeholder character in the cp command line so that arguments can be placed after the file name.
find /path -type f -print0 | xargs -0 -I % cp % .
Tested with xargs (GNU findutils) 4.4.0
You can limit the number of lines, or arguments (if there are spaces between each argument) using the --max-lines or --max-args flags, respectively.
-L max-lines
Use at most max-lines nonblank input lines per command line. Trailing blanks cause an input line to be logically continued on the next input
line. Implies -x.
--max-lines[=max-lines], -l[max-lines]
Synonym for the -L option. Unlike -L, the max-lines argument is optional. If max-args is not specified, it defaults to one. The -l option
is deprecated since the POSIX standard specifies -L instead.
--max-args=max-args, -n max-args
Use at most max-args arguments per command line. Fewer than max-args arguments will be used if the size (see the -s option) is exceeded,
unless the -x option is given, in which case xargs will exit.
#Draemon answers seems to be right with "-0" even with space in the file.
I was trying the xargs command and I found that "-0" works perfectly with "-L". even the spaces are treated (if input was null terminated ). the following is an example :
#touch "file with space"
#touch "file1"
#touch "file2"
The following will split the nulls and execute the command on each argument in the list :
#find . -name 'file*' -print0 | xargs -0 -L1
./file with space
./file1
./file2
so -L1 will execute the argument on each null terminated character if used with "-0". To see the difference try :
#find . -name 'file*' -print0 | xargs -0 | xargs -L1
./file with space ./file1 ./file2
even this will execute once :
#find . -name 'file*' -print0 | xargs -0 | xargs -0 -L1
./file with space ./file1 ./file2
The command will execute once as the "-L" now doesn't split on null byte. you need to provide both "-0" and "-L" to work.
It seems I don't have enough reputation to add a comment to Tobia's answer above, so I am adding this "answer" to help those of us wanting to experiment with xargs the same way on the Windows platforms.
Here is a windows batch file that does the same thing as Tobia's quickly coded "show" script:
#echo off
REM
REM cool trick of using "set" to echo without new line
REM (from: http://www.psteiner.com/2012/05/windows-batch-echo-without-new-line.html)
REM
if "%~1" == "" (
exit /b
)
<nul set /p=Args: "%~1"
shift
:start
if not "%~1" == "" (
<nul set /p=, "%~1"
shift
goto start
)
echo.
In your example, the point of piping the output of find to xargs is that the standard behavior of find's -exec option is to execute the command once for each found file. If you're using find, and you want its standard behavior, then the answer is simple - don't use xargs to begin with.
execute ant task clean-all on every build.xml on current or sub-folder.
find . -name 'build.xml' -exec ant -f {} clean-all \;