x=$(find . -name "*.txt") echo $x
if I run the above piece of code in Bash shell, what I get is a string containing several file names separated by blank, not a list.
Of course, I can further separate them by blank to get a list, but I'm sure there is a better way to do it.
So what is the best way to loop through the results of a find
command?
Execute the following command to insert the file's name, followed by a newline, followed by the text Loops Rule! into each file: for FILE in *; do echo -e "$FILE\nLoops Rule\!" > $FILE; done.
Shopt is a built-in command in Unix-like operating systems, such as macOS and Linux distributions. The “shopt” command provides control over many settings that are used to tweak the operations in a Bash shell.
TL;DR: If you're just here for the most correct answer, you probably want my personal preference (see the bottom of this post):
# execute `process` once for each file find . -name '*.txt' -exec process {} \;
If you have time, read through the rest to see several different ways and the problems with most of them.
The full answer:
The best way depends on what you want to do, but here are a few options. As long as no file or folder in the subtree has whitespace in its name, you can just loop over the files:
for i in $x; do # Not recommended, will break on whitespace process "$i" done
Marginally better, cut out the temporary variable x
:
for i in $(find -name \*.txt); do # Not recommended, will break on whitespace process "$i" done
It is much better to glob when you can. White-space safe, for files in the current directory:
for i in *.txt; do # Whitespace-safe but not recursive. process "$i" done
By enabling the globstar
option, you can glob all matching files in this directory and all subdirectories:
# Make sure globstar is enabled shopt -s globstar for i in **/*.txt; do # Whitespace-safe and recursive process "$i" done
In some cases, e.g. if the file names are already in a file, you may need to use read
:
# IFS= makes sure it doesn't trim leading and trailing whitespace # -r prevents interpretation of \ escapes. while IFS= read -r line; do # Whitespace-safe EXCEPT newlines process "$line" done < filename
read
can be used safely in combination with find
by setting the delimiter appropriately:
find . -name '*.txt' -print0 | while IFS= read -r -d '' line; do process "$line" done
For more complex searches, you will probably want to use find
, either with its -exec
option or with -print0 | xargs -0
:
# execute `process` once for each file find . -name \*.txt -exec process {} \; # execute `process` once with all the files as arguments*: find . -name \*.txt -exec process {} + # using xargs* find . -name \*.txt -print0 | xargs -0 process # using xargs with arguments after each filename (implies one run per filename) find . -name \*.txt -print0 | xargs -0 -I{} process {} argument
find
can also cd into each file's directory before running a command by using -execdir
instead of -exec
, and can be made interactive (prompt before running the command for each file) using -ok
instead of -exec
(or -okdir
instead of -execdir
).
*: Technically, both find
and xargs
(by default) will run the command with as many arguments as they can fit on the command line, as many times as it takes to get through all the files. In practice, unless you have a very large number of files it won't matter, and if you exceed the length but need them all on the same command line, you're SOL find a different way.
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