I use command of find, for example:
find . -name "*.log" -exec grep "running" {} \;
why the command of find need {} , a blank and \?
This is because of the -exec parameter: the {} is a placeholder for the file that will be passed to the command.
the semicolon (;) tells find that the -exec argument list is over, but since ; is also a shell operator, you need to escape it so that it reaches find: \;
-exec works like this: for every file that is found, the first argument after -exec (the command) is executed and all parameters up until the ; are passed as arguments to the command. The {} is then replaced by the current filename that is found by find.
{} is a placeholder for path, which find replaces with the actual found path.
\; terminates find's exec arguments. Without \ shell would treat it as shell statement terminator, hence it needs to be quoted with \ for the shell to pass ; it to find.
I'd say that ; was an unfortunate choice for find exec command terminator.
Note that {} \; sequence can be replaced with {} +:
-exec command {} +
This variant of the -exec action runs the specified command on
the selected files, but the command line is built by appending
each selected file name at the end; the total number of invoca‐
tions of the command will be much less than the number of
matched files. The command line is built in much the same way
that xargs builds its command lines. Only one instance of `{}'
is allowed within the command. The command is executed in the
starting directory.
Just read the manpages
-exec command ;
Execute command; true if 0 status is returned. All following
arguments to find are taken to be arguments to the command until
an argument consisting of `;' is encountered. The string `{}'
is replaced by the current file name being processed everywhere
it occurs in the arguments to the command, not just in arguments
where it is alone, as in some versions of find. Both of these
constructions might need to be escaped (with a `\') or quoted to
protect them from expansion by the shell. See the EXAMPLES sec‐
tion for examples of the use of the -exec option. The specified
command is run once for each matched file. The command is exe‐
cuted in the starting directory. There are unavoidable secu‐
rity problems surrounding use of the -exec action; you should
use the -execdir option instead.
The backslash is an escape to protect the semicolon from being misinterpreted.
The braces are placeholders for the full path outputted by find.
Related
Why does running this command give me error message: No such file or directory ?
for i in `find ~/desktop -name '*.py'` ; do ./$i ; done
The complete error message makes it much more clear what the problem is:
bash: .//home/youruser/desktop/foo.py: No such file or directory
You can see that there is indeed no such file:
$ .//home/youruser/desktop/foo.py
bash: .//home/youruser/desktop/foo.py: No such file or directory
$ ls -l .//home/youruser/desktop/foo.py
ls: cannot access './/home/youruser/desktop/foo.py': No such file or directory
Here's instead how you can run a file /home/youruser/desktop/foo.py:
$ /home/youruser/desktop/foo.py
Hello World
So to run it in your loop, you can do:
for i in `find ~/desktop -name '*.py'` ; do $i ; done
Here's a better way of doing the same thing:
find ~/desktop -name '*.py' -exec {} \;
or with a shell loop:
find ~/desktop -name '*.py' -print0 | while IFS= read -d '' -r file; do "$file"; done
For an explanation of what ./ is and does, and why it makes no sense here, see this question
Try find and exec option. http://man7.org/linux/man-pages/man1/find.1.html
-exec command ;
Execute command; true if 0 status is returned. All following
arguments to find are taken to be arguments to the command
until an argument consisting of `;' is encountered. The
string `{}' is replaced by the current file name being
processed everywhere it occurs in the arguments to the
command, not just in arguments where it is alone, as in some
versions of find. Both of these constructions might need to
be escaped (with a `\') or quoted to protect them from
expansion by the shell. See the EXAMPLES section for examples
of the use of the -exec option. The specified command is run
once for each matched file. The command is executed in the
starting directory. There are unavoidable security problems
surrounding use of the -exec action; you should use the
-execdir option instead.
-exec command {} +
This variant of the -exec action runs the specified command on
the selected files, but the command line is built by appending
each selected file name at the end; the total number of
invocations of the command will be much less than the number
of matched files. The command line is built in much the same
way that xargs builds its command lines. Only one instance of
`{}' is allowed within the command, and (when find is being
invoked from a shell) it should be quoted (for example, '{}')
to protect it from interpretation by shells. The command is
executed in the starting directory. If any invocation with
the `+' form returns a non-zero value as exit status, then
find returns a non-zero exit status. If find encounters an
error, this can sometimes cause an immediate exit, so some
pending commands may not be run at all. This variant of -exec
always returns true.
The paths returned by the find statement will be absolute paths, like ~/desktop/program.py. If you put ./ in front of them, you get paths like ./~/desktop/ which don’t exist.
Replace ./$i with "$i" (the quotes to take care of file names with spaces etc.).
You should use $i and not ./$i
I was doing the same thing this exact moment. I wanted a script to find if there's any flac files in the directory and convert it to opus.
Here is my solution:
if test -n "$(find ./ -maxdepth 1 -name '*.flac' -print -quit)"
then
do this
else
do nothing
fi
This question already has answers here:
Why are the backslash and semicolon required with the find command's -exec option?
(2 answers)
Closed 9 years ago.
This is a relatively simple command, so if a duplicate exists and someone could refer me, I'm sorry and I'll delete/close this question.
Man page for find
find . -type f -exec file '{}' \;
Runs 'file' on every file in or below the current directory. Notice that the braces are enclosed in single quote marks to protect them from interpretation
as shell script punctuation. The semicolon is similarly protected by the use of a backslash, though ';' could have been used in that case also.
I do not understand the notation \;. What in the world is that?
In the find command, the action -exec is followed by a command and that command's arguments. Because there can be any number of arguments, find needs some way of knowing when it ends. The semicolon is what tells find that it has reached the end of the command's arguments.
Left to their own devices, most shells would eat the semicolon. We want that semicolon to be passed to the find command. Therefore, we escape it with a backslash. This tells the shell to treat the semicolon as just one of the arguments to the find command.
MORE: Why not, one may ask, just assume that the exec command's argument just go to the end of the line? Why do we need to signal an end to the exec command's arguments at all? The reason is that find has advanced features. Just for example, consider:
find . -name '*.pdf' -exec echo Yes, we have a pdf: {} \; -o -exec echo No, not a pdf: {} \;
I have begun to combine different commands in the linux terminal. I am wondering why the backslash and semicolon are required for a command such as:
find ./ -name 'blabla' -exec cp {} ./test \;
when a simple cp command is simply:
cp randomfile ./test
without the \;
Are they to clearly indicate the end of a command, or is it simply required in the documentation? What is the underlying principle?
The backslash before the semicolon is used, because ; is one of list operators (or &&, ||) for separating shell commands. In example:
command1; command2
The find utility is using ; or + to terminate the shell commands invoked by -exec.
So to avoid special shell characters from interpretation, they need to be escaped with a backslash to remove any special meaning for the next character read and for line continuation.
Therefore the following example syntax is allowed for find command:
find . -exec echo {} \;
find . -exec echo {} ';'
find . -exec echo {} ";"
find . -exec echo {} \+
find . -exec echo {} +
See also:
Using semicolon (;) vs plus (+) with exec in find
Simple unix command, what is the {} and \; for
from "man find":
All following
arguments to find are taken to be arguments to the command until
an argument consisting of ';' is encountered.
find needs to know when the arguments of exec are terminated. It is natural to terminate a shell command with ; because also the shell uses this character. For the very same reason such a character must be escaped when inserted through the shell.
I would like to pass the output list of elements of a command as a parameter of another command. I have found some other pages:
How to display the output of a Linux command on stdout and also pipe it to another command?
Use output of bash command (with pipe) as a parameter for another command
but they seem to be more complex.
I just would like to copy a file to every result of a call to the Linux find command.
What is wrong here?:
find . -name myFile 2>&1 | cp /home/myuser/myFile $1
Thanks
This is what you want:
find . -name myFile -exec cp /home/myuser/myFile {} ';'
A breakdown / explanation of this:
find: invoking the find command
.: start search from current working directory.
Since no depth flags are specified, this will search recursively for all subfolders
-name myFile: find files with the explicit name myFile
-exec: for the search results, perform additional commands with them
cp /home/myuser/myFile {}: copies /home/myuser/myFile to overwrite each result returned by find to ; think of {} as where each search result goes.
';': used to separate different commands to be run after find
There are a couple of ways to solve this, depending on whether you need to worry about files with spaces or other special characters in their names.
If none of the filenames have spaces or special characters (they consist only of letters, numbers, dashes, and underscores), then the following is a simple solution that will work. You can use $(command) to execute a command, and substitute the results into the arguments of another command. The shell will split the result on spaces, tabs, or newlines, and for assign each value to $f in turn, and run the command on each value.
for f in $(find . -name myFile)
do
cp something $f
done
If you do have spaces or tabs, you could use find's -exec option. You pass -exec command args, putting {} where you want the filename to be substituted, and ending the arguments with a ;. You need to quote the {} and ; so that the shell doesn't interpret them.
find . -name myFile -exec cp something "{}" \;
Sometimes -exec is not sufficient. For example, in this question, they wanted to use Bash parameter expansion to compute the filename. In order to do that, you need to pass -exec bash -c 'your command', but then you will run into quoting problems with the {} substitution. To solve this, you can use -print0 from find to print the results delimited with null characters (which are invalid in filenames), and pipe it to a while read loop that splits parameters on nulls:
find . -name myFile -print0 | (while read -d $'\0' f; do
cp something "$f"
done)
The pipe will send the output of one program to the input of another. cp does not read from its input stream at the terminal, it merely uses the arguments on the command line.
You want to either use xargs with the pipe or find's exec argument instead of pipes.
find . -name myFile 2>&1 | xargs -I {} cp /home/myuser/myFile {}
Note: option -I {} defines {} as the place holder you could alternatively use someother placeholder if it conflicts with command to be executed.
I managed to find several files with the find command.
the files are of the type file_sakfksanf.txt, file_afsjnanfs.pdf, file_afsnjnjans.cpp,
now I want to rename them with the rename and -exec command to
mywish_sakfksanf.txt, mywish_afsjnanfs.pdf, mywish_afsnjnjans.cpp
that only the first prefix is changed. I am trying for some time, so don't blame me for being stupid.
If you read through the -exec section of the man pages for find you will come across the {} string that allows you to use the matches as arguments within -exec. This will allow you to use rename on your find matches in the following way:
find . -name 'file_*' -exec rename 's/file_/mywish_/' {} \;
From the manual:
-exec command ;
Execute command; true if 0 status is returned. All following
arguments to find are taken to be arguments to the command until an
argument consisting of ;' is encountered. The string{}' is replaced
by the current file name being processed everywhere it occurs in the
arguments to the command, not just in arguments where it is alone, as
in some versions of find. Both of these constructions might need to
be escaped (with a `\') or quoted to protect them from expansion by
the shell. See the EXAMPLES section for examples of the use of the
-exec option. The specified command is run once for each matched file. The command is executed in the starting directory.There are
unavoidable security problems surrounding use of the -exec action;
you should use the -execdir option instead.
Although you asked for a find/exec solution, as Mark Reed suggested, you might want to consider piping your results to xargs. If you do, make sure to use the -print0 option with find and either the -0 or -null option with xargs to avoid unexpected behaviour resulting from whitespace or shell metacharacters appearing in your file names. Also, consider using the + version of -exec (also in the manual) as this is the POSIX spec for find and should therefore be more portable if you are wanting to run your command elsewhere (not always true); it also builds its command line in a way similar to xargs which should result in less invocations of rename.
Don't think there's a way you can do this with just find, you'll need to create a script:
#!/bin/bash
NEW=`echo $1 | sed -e 's/file_/mywish_/'`
mv $1 ${NEW}
THen you can:
find ./ -name 'file_*' -exec my_script {} \;