Related
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?
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.
What ever you do, don't use a for loop:
# Don't do this
for file in $(find . -name "*.txt")
do
…code using "$file"
done
Three reasons:
For the for loop to even start, the find must run to completion.
If a file name has any whitespace (including space, tab or newline) in it, it will be treated as two separate names.
Although now unlikely, you can overrun your command line buffer. Imagine if your command line buffer holds 32KB, and your for loop returns 40KB of text. That last 8KB will be dropped right off your for loop and you'll never know it.
Always use a while read construct:
find . -name "*.txt" -print0 | while read -d $'\0' file
do
…code using "$file"
done
The loop will execute while the find command is executing. Plus, this command will work even if a file name is returned with whitespace in it. And, you won't overflow your command line buffer.
The -print0 will use the NULL as a file separator instead of a newline and the -d $'\0' will use NULL as the separator while reading.
find . -name "*.txt"|while read fname; do
echo "$fname"
done
Note: this method and the (second) method shown by bmargulies are safe to use with white space in the file/folder names.
In order to also have the - somewhat exotic - case of newlines in the file/folder names covered, you will have to resort to the -exec predicate of find like this:
find . -name '*.txt' -exec echo "{}" \;
The {} is the placeholder for the found item and the \; is used to terminate the -exec predicate.
And for the sake of completeness let me add another variant - you gotta love the *nix ways for their versatility:
find . -name '*.txt' -print0|xargs -0 -n 1 echo
This would separate the printed items with a \0 character that isn't allowed in any of the file systems in file or folder names, to my knowledge, and therefore should cover all bases. xargs picks them up one by one then ...
Filenames can include spaces and even control characters. Spaces are (default) delimiters for shell expansion in bash and as a result of that x=$(find . -name "*.txt") from the question is not recommended at all. If find gets a filename with spaces e.g. "the file.txt" you will get 2 separated strings for processing, if you process x in a loop. You can improve this by changing delimiter (bash IFS Variable) e.g. to \r\n, but filenames can include control characters - so this is not a (completely) safe method.
From my point of view, there are 2 recommended (and safe) patterns for processing files:
1. Use for loop & filename expansion:
for file in ./*.txt; do
[[ ! -e $file ]] && continue # continue, if file does not exist
# single filename is in $file
echo "$file"
# your code here
done
2. Use find-read-while & process substitution
while IFS= read -r -d '' file; do
# single filename is in $file
echo "$file"
# your code here
done < <(find . -name "*.txt" -print0)
Remarks
on Pattern 1:
bash returns the search pattern ("*.txt") if no matching file is found - so the extra line "continue, if file does not exist" is needed. see Bash Manual, Filename Expansion
shell option nullglob can be used to avoid this extra line.
"If the failglob shell option is set, and no matches are found, an error message is printed and the command is not executed." (from Bash Manual above)
shell option globstar: "If set, the pattern ‘**’ used in a filename expansion context will match all files and zero or more directories and subdirectories. If the pattern is followed by a ‘/’, only directories and subdirectories match." see Bash Manual, Shopt Builtin
other options for filename expansion: extglob, nocaseglob, dotglob & shell variable GLOBIGNORE
on Pattern 2:
filenames can contain blanks, tabs, spaces, newlines, ... to process filenames in a safe way, find with -print0 is used: filename is printed with all control characters & terminated with NUL. see also Gnu Findutils Manpage, Unsafe File Name Handling, safe File Name Handling, unusual characters in filenames. See David A. Wheeler below for detailed discussion of this topic.
There are some possible patterns to process find results in a while loop. Others (kevin, David W.) have shown how to do this using pipes:
files_found=1
find . -name "*.txt" -print0 |
while IFS= read -r -d '' file; do
# single filename in $file
echo "$file"
files_found=0 # not working example
# your code here
done
[[ $files_found -eq 0 ]] && echo "files found" || echo "no files found"
When you try this piece of code, you will see, that it does not work: files_found is always "true" & the code will always echo "no files found". Reason is: each command of a pipeline is executed in a separate subshell, so the changed variable inside the loop (separate subshell) does not change the variable in the main shell script. This is why I recommend using process substitution as the "better", more useful, more general pattern.See I set variables in a loop that's in a pipeline. Why do they disappear... (from Greg's Bash FAQ) for a detailed discussion on this topic.
Additional References & Sources:
Gnu Bash Manual, Pattern Matching
Filenames and Pathnames in Shell: How to do it Correctly, David A. Wheeler
Why you don't read lines with "for", Greg's Wiki
Why you shouldn't parse the output of ls(1), Greg's Wiki
Gnu Bash Manual, Process Substitution
(Updated to include #Socowi's execellent speed improvement)
With any $SHELL that supports it (dash/zsh/bash...):
find . -name "*.txt" -exec $SHELL -c '
for i in "$#" ; do
echo "$i"
done
' {} +
Done.
Original answer (shorter, but slower):
find . -name "*.txt" -exec $SHELL -c '
echo "$0"
' {} \;
If you can assume the file names don't contain newlines, you can read the output of find into a Bash array using the following command:
readarray -t x < <(find . -name '*.txt')
Note:
-t causes readarray to strip newlines.
It won't work if readarray is in a pipe, hence the process substitution.
readarray is available since Bash 4.
Bash 4.4 and up also supports the -d parameter for specifying the delimiter. Using the null character, instead of newline, to delimit the file names works also in the rare case that the file names contain newlines:
readarray -d '' x < <(find . -name '*.txt' -print0)
readarray can also be invoked as mapfile with the same options.
Reference: https://mywiki.wooledge.org/BashFAQ/005#Loading_lines_from_a_file_or_stream
# Doesn't handle whitespace
for x in `find . -name "*.txt" -print`; do
process_one $x
done
or
# Handles whitespace and newlines
find . -name "*.txt" -print0 | xargs -0 -n 1 process_one
I like to use find which is first assigned to variable and IFS switched to new line as follow:
FilesFound=$(find . -name "*.txt")
IFSbkp="$IFS"
IFS=$'\n'
counter=1;
for file in $FilesFound; do
echo "${counter}: ${file}"
let counter++;
done
IFS="$IFSbkp"
As commented by #Konrad Rudolph this will not work with "new lines" in file name. I still think it is handy as it covers most of the cases when you need to loop over command output.
As already posted on the top answer by Kevin, the best solution is to use a for loop with bash glob, but as bash glob is not recursive by default, this can be fixed by a bash recursive function:
#!/bin/bash
set -x
set -eu -o pipefail
all_files=();
function get_all_the_files()
{
directory="$1";
for item in "$directory"/* "$directory"/.[^.]*;
do
if [[ -d "$item" ]];
then
get_all_the_files "$item";
else
all_files+=("$item");
fi;
done;
}
get_all_the_files "/tmp";
for file_path in "${all_files[#]}"
do
printf 'My file is "%s"\n' "$file_path";
done;
Related questions:
Bash loop through directory including hidden file
Recursively list files from a given directory in Bash
ls command: how can I get a recursive full-path listing, one line per file?
List files recursively in Linux CLI with path relative to the current directory
Recursively List all directories and files
bash script, create array of all files in a directory
How can I creates array that contains the names of all the files in a folder?
How can I creates array that contains the names of all the files in a folder?
How to get the list of files in a directory in a shell script?
based on other answers and comment of #phk, using fd #3:
(which still allows to use stdin inside the loop)
while IFS= read -r f <&3; do
echo "$f"
done 3< <(find . -iname "*filename*")
You can put the filenames returned by find into an array like this:
array=()
while IFS= read -r -d ''; do
array+=("$REPLY")
done < <(find . -name '*.txt' -print0)
Now you can just loop through the array to access individual items and do whatever you want with them.
Note: It's white space safe.
You can store your find output in array if you wish to use the output later as:
array=($(find . -name "*.txt"))
Now to print the each element in new line, you can either use for loop iterating to all the elements of array, or you can use printf statement.
for i in ${array[#]};do echo $i; done
or
printf '%s\n' "${array[#]}"
You can also use:
for file in "`find . -name "*.txt"`"; do echo "$file"; done
This will print each filename in newline
To only print the find output in list form, you can use either of the following:
find . -name "*.txt" -print 2>/dev/null
or
find . -name "*.txt" -print | grep -v 'Permission denied'
This will remove error messages and only give the filename as output in new line.
If you wish to do something with the filenames, storing it in array is good, else there is no need to consume that space and you can directly print the output from find.
I think using this piece of code (piping the command after while done):
while read fname; do
echo "$fname"
done <<< "$(find . -name "*.txt")"
is better than this answer because while loop is executed in a subshell according to here, if you use this answer and variable changes cannot be seen after while loop if you want to modify variables inside the loop.
function loop_through(){
length_="$(find . -name '*.txt' | wc -l)"
length_="${length_#"${length_%%[![:space:]]*}"}"
length_="${length_%"${length_##*[![:space:]]}"}"
for i in {1..$length_}
do
x=$(find . -name '*.txt' | sort | head -$i | tail -1)
echo $x
done
}
To grab the length of the list of files for loop, I used the first command "wc -l".
That command is set to a variable.
Then, I need to remove the trailing white spaces from the variable so the for loop can read it.
find <path> -xdev -type f -name *.txt -exec ls -l {} \;
This will list the files and give details about attributes.
Another alternative is to not use bash, but call Python to do the heavy lifting. I recurred to this because bash solutions as my other answer were too slow.
With this solution, we build a bash array of files from inline Python script:
#!/bin/bash
set -eu -o pipefail
dsep=":" # directory_separator
base_directory=/tmp
all_files=()
all_files_string="$(python3 -c '#!/usr/bin/env python3
import os
import sys
dsep="'"$dsep"'"
base_directory="'"$base_directory"'"
def log(*args, **kwargs):
print(*args, file=sys.stderr, **kwargs)
def check_invalid_characther(file_path):
for thing in ("\\", "\n"):
if thing in file_path:
raise RuntimeError(f"It is not allowed {thing} on \"{file_path}\"!")
def absolute_path_to_relative(base_directory, file_path):
relative_path = os.path.commonprefix( [ base_directory, file_path ] )
relative_path = os.path.normpath( file_path.replace( relative_path, "" ) )
# if you use Windows Python, it accepts / instead of \\
# if you have \ on your files names, rename them or comment this
relative_path = relative_path.replace("\\", "/")
if relative_path.startswith( "/" ):
relative_path = relative_path[1:]
return relative_path
for directory, directories, files in os.walk(base_directory):
for file in files:
local_file_path = os.path.join(directory, file)
local_file_name = absolute_path_to_relative(base_directory, local_file_path)
log(f"local_file_name {local_file_name}.")
check_invalid_characther(local_file_name)
print(f"{base_directory}{dsep}{local_file_name}")
' | dos2unix)";
if [[ -n "$all_files_string" ]];
then
readarray -t temp <<< "$all_files_string";
all_files+=("${temp[#]}");
fi;
for item in "${all_files[#]}";
do
OLD_IFS="$IFS"; IFS="$dsep";
read -r base_directory local_file_name <<< "$item"; IFS="$OLD_IFS";
printf 'item "%s", base_directory "%s", local_file_name "%s".\n' \
"$item" \
"$base_directory" \
"$local_file_name";
done;
Related:
os.walk without hidden folders
How to do a recursive sub-folder search and return files in a list?
How to split a string into an array in Bash?
How about if you use grep instead of find?
ls | grep .txt$ > out.txt
Now you can read this file and the filenames are in the form of a list.
Within a certain directory I have many directories containing a bunch of text files. I’m trying to write a script that concatenates only those files in each directory that have the string ‘R1’ in their filename into one file within that specific directory, and those that have ‘R2’ in another . This is what I wrote but it’s not working.
#!/bin/bash
for f in */*.fastq; do
if grep 'R1' $f ; then
cat "$f" >> R1.fastq
fi
if grep 'R2' $f ; then
cat "$f" >> R2.fastq
fi
done
I get no errors and the files are created as intended but they are empty files. Can anyone tell me what I’m doing wrong?
Thank you all for the fast and detailed responses! I think I wasn't very clear in my question, but I need the script to only concatenate the files within each specific directory so that each directory has a new file ( R1 and R2). I tried doing
cat /*R1*.fastq >*/R1.fastq
but it gave me an ambiguous redirect error. I also tried Charles Duffy's for loop but looping through the directories and doing a nested loop to run though each file within a directory like so
for f in */; do
for d in "$f"/*.fastq;do
case "$d" in
*R1*) cat "$d" >&3
*R2*) cat "$d" >&4
esac
done 3>R1.fastq 4>R2.fastq
done
but it was giving an unexpected token error regarding ')'.
Sorry in advance if I'm missing something elementary, I'm still very new to bash.
A Note To The Reader
Please review edit history on the question in considering this answer; several parts have been made less relevant by question edits.
One cat Per Output File
For the purpose at hand, you can probably just let shell globbing do all the work (if R1 or R2 will be in the filenames, as opposed to the directory names):
set -x # log what's happening!
cat */*R1*.fastq >R1.fastq
cat */*R2*.fastq >R2.fastq
One find Per Output File
If it's a really large number of files, by contrast, you might need find:
find . -mindepth 2 -maxdepth 2 -type f -name '*R1*.fastq' -exec cat '{}' + >R1.fastq
find . -mindepth 2 -maxdepth 2 -type f -name '*R2*.fastq' -exec cat '{}' + >R2.fastq
...this is because of the OS-dependent limit on command-line length; the find command given above will put as many arguments onto each cat command as possible for efficiency, but will still split them up into multiple invocations where otherwise the limit would be exceeded.
Iterate-And-Test
If you really do want to iterate over everything, and then test the names, consider a case statement for the job, which is much more efficient than using grep to check just one line:
for f in */*.fastq; do
case $f in
*R1*) cat "$f" >&3
*R2*) cat "$f" >&4
esac
done 3>R1.fastq 4>R2.fastq
Note the use of file descriptors 3 and 4 to write to R1.fastq and R2.fastq respectively -- that way we're only opening the output files once (and thus truncating them exactly once) when the for loop starts, and reusing those file descriptors rather than re-opening the output files at the beginning of each cat. (That said, running cat once per file -- which find -exec {} + avoids -- is probably more overhead on balance).
Operating Per-Directory
All of the above can be updated to work on a per-directory basis quite trivially. For example:
for d in */; do
find "$d" -name R1.fastq -prune -o -name '*R1*.fastq' -exec cat '{}' + >"$d/R1.fastq"
find "$d" -name R2.fastq -prune -o -name '*R2*.fastq' -exec cat '{}' + >"$d/R2.fastq"
done
There are only two significant changes:
We're no longer specifying -mindepth, to ensure that our input files only come from subdirectories.
We're excluding R1.fastq and R2.fastq from our input files, so we never try to use the same file as both input and output. This is a consequence of the prior change: Previously, our output files couldn't be considered as input because they didn't meet the minimum depth.
Your grep is searching the file contents instead of file name. You could rewrite it this way:
for f in */*.fastq; do
[[ -f $f ]] || continue
if [[ $f = *R1* ]]; then
cat "$f" >> R1.fastq
elif [[ $f = *R2* ]]; then
cat "$f" >> R2.fastq
fi
done
Find in a forloop might suit this:
for i in R1 R2
do
find . -type f -name "*${i}*" -exec cat '{}' + >"$i.txt"
done
What do I have to type to get a list of files in the current directory satisfying the following conditions?
Hidden files (starting with ".") should NOT be included
Folder names should not be included
The filenames should include their extension
Filenames with spaces should not be broken up into multiple list items
(I intend to loop over the results in a foor loop in bash script.)
Using just bash:
files=()
for f in *; do [[ -d $f ]] || files+=("$f"); done
printf "%s\n" "${files[#]}"
How about just using * and then skipping over the directories as the first step in your loop?
for F in * ; do
if test -d "$F" ; then continue ; fi
echo "$F"
done
find . -maxdepth 1 ! -name '.*' -type f
should work fine for your needs
maxdepth 1 -> Searches only in current dir
! -name '.*' -> Searches files NOT matching name pattern '.*'
type f -> Searches only files, not dirs
You can try this:
find $folderPath -type f -printf "%f\n" | grep -v '^[.].*'
you only have to change the $folderPath.
Explanation
find $folderPath -type f -printf "%f\n"
With find command you can search into the folder with a several options.
'-type f' search only the files, if you want filter by folder, you only have to change the 'f' for 'd'
'-print "%f\n"' format the output of the command. '%f' extract the filename and '\n' add a return.
'|' is a pipe. With the pipe you can use the output of a command to use it like a input var in other command.
grep -v '^[.].*'
grep is a command to looking for a regex expresion into a input text.
with the option '-v '^[.].*', you exclude the values that contains the regex. In this case, the words that start with a . (dot).
To close the explanation, if you use another '|' (pipe) you can process every result of the command like the input for another. This has a better performance, because the output is in a Stream, and need less memory to process the result.
In the directories ~/temp/a/foo/ and ~/temp/b/foo foo/ I have some files named bar1, bar2, bar bar1, bar bar2, etc.
I am trying to write a line of Bash that copies all these files in a directory containing "foo" as last part of the name to the folder above the respective "foo" folder.
As long as there are no spaces in the file names, this is an easy task, but the two following commands fail when dealing with the foo foo directory:
for dir in `find . -type d -name '*foo'` ; do cp $dir/* "$(echo $dir|sed 's_foo__g')" ; done
(The cp command fails to see the last foo of "foo foo" as part of the same directory name.)
for dir in `find . -type d -name '*foo'` ; do cp "$dir/*" "$(echo $dir|sed 's_foo__g')" ; done
("$dir/*" is not expanded.)
Attempts like replacing $dir/* with "$(echo $dir/*)" have been even less successful.
Is there an easy way to expand $dir/* so that cp understands?
Not only is a for loop wrong -- sed is also not the right tool for this job.
while IFS= read -r -d '' dir; do
cp "$dir" "${dir/foo/}"
done < <(find . -type d -name '*foo' -print0)
Using -print0 on the find (and IFS= read -r -d '') ensures that filenames with newlines won't mess you up.
Using the < <(...) construct ensures that if the inside of your loop sets variables, changes directory state, or does similar things, those changes will survive (the right-hand side of a pipeline is in a subshell in bash, so piping into a while loop would mean that any changes to the shell's state made inside that while loop would be discarded on its exit otherwise).
Using ${dir/foo/} is vastly more efficient than invoking sed, as it does the string replacement internal to bash.
The problem here is not with cp, but with for, because by default it splits the output of your subshell by words, not by directory names.
A lazy workaround is to use while instead and process the list of directories line by line like this:
find . -type d -name '*foo' | while read dir; do cp "$dir"/* "$(echo $dir | sed 's_foo__g')" ; done
This should fix your problem with spaces, but this is by no means a foolproof solution.
See Charles Duffy's answer for a more accurate solution.
Rename ~/temp/b/foo foo/ to something without spaces, e.g. ~/temp/b/foo_foo/ and do what you were trying to do again. After that you can rename it back to the original, with space, if you really have to. BTW. myself I never use file names containing spaces, simply to avoid complications like the one you are facing now.
x=$(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?
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.
What ever you do, don't use a for loop:
# Don't do this
for file in $(find . -name "*.txt")
do
…code using "$file"
done
Three reasons:
For the for loop to even start, the find must run to completion.
If a file name has any whitespace (including space, tab or newline) in it, it will be treated as two separate names.
Although now unlikely, you can overrun your command line buffer. Imagine if your command line buffer holds 32KB, and your for loop returns 40KB of text. That last 8KB will be dropped right off your for loop and you'll never know it.
Always use a while read construct:
find . -name "*.txt" -print0 | while read -d $'\0' file
do
…code using "$file"
done
The loop will execute while the find command is executing. Plus, this command will work even if a file name is returned with whitespace in it. And, you won't overflow your command line buffer.
The -print0 will use the NULL as a file separator instead of a newline and the -d $'\0' will use NULL as the separator while reading.
find . -name "*.txt"|while read fname; do
echo "$fname"
done
Note: this method and the (second) method shown by bmargulies are safe to use with white space in the file/folder names.
In order to also have the - somewhat exotic - case of newlines in the file/folder names covered, you will have to resort to the -exec predicate of find like this:
find . -name '*.txt' -exec echo "{}" \;
The {} is the placeholder for the found item and the \; is used to terminate the -exec predicate.
And for the sake of completeness let me add another variant - you gotta love the *nix ways for their versatility:
find . -name '*.txt' -print0|xargs -0 -n 1 echo
This would separate the printed items with a \0 character that isn't allowed in any of the file systems in file or folder names, to my knowledge, and therefore should cover all bases. xargs picks them up one by one then ...
Filenames can include spaces and even control characters. Spaces are (default) delimiters for shell expansion in bash and as a result of that x=$(find . -name "*.txt") from the question is not recommended at all. If find gets a filename with spaces e.g. "the file.txt" you will get 2 separated strings for processing, if you process x in a loop. You can improve this by changing delimiter (bash IFS Variable) e.g. to \r\n, but filenames can include control characters - so this is not a (completely) safe method.
From my point of view, there are 2 recommended (and safe) patterns for processing files:
1. Use for loop & filename expansion:
for file in ./*.txt; do
[[ ! -e $file ]] && continue # continue, if file does not exist
# single filename is in $file
echo "$file"
# your code here
done
2. Use find-read-while & process substitution
while IFS= read -r -d '' file; do
# single filename is in $file
echo "$file"
# your code here
done < <(find . -name "*.txt" -print0)
Remarks
on Pattern 1:
bash returns the search pattern ("*.txt") if no matching file is found - so the extra line "continue, if file does not exist" is needed. see Bash Manual, Filename Expansion
shell option nullglob can be used to avoid this extra line.
"If the failglob shell option is set, and no matches are found, an error message is printed and the command is not executed." (from Bash Manual above)
shell option globstar: "If set, the pattern ‘**’ used in a filename expansion context will match all files and zero or more directories and subdirectories. If the pattern is followed by a ‘/’, only directories and subdirectories match." see Bash Manual, Shopt Builtin
other options for filename expansion: extglob, nocaseglob, dotglob & shell variable GLOBIGNORE
on Pattern 2:
filenames can contain blanks, tabs, spaces, newlines, ... to process filenames in a safe way, find with -print0 is used: filename is printed with all control characters & terminated with NUL. see also Gnu Findutils Manpage, Unsafe File Name Handling, safe File Name Handling, unusual characters in filenames. See David A. Wheeler below for detailed discussion of this topic.
There are some possible patterns to process find results in a while loop. Others (kevin, David W.) have shown how to do this using pipes:
files_found=1
find . -name "*.txt" -print0 |
while IFS= read -r -d '' file; do
# single filename in $file
echo "$file"
files_found=0 # not working example
# your code here
done
[[ $files_found -eq 0 ]] && echo "files found" || echo "no files found"
When you try this piece of code, you will see, that it does not work: files_found is always "true" & the code will always echo "no files found". Reason is: each command of a pipeline is executed in a separate subshell, so the changed variable inside the loop (separate subshell) does not change the variable in the main shell script. This is why I recommend using process substitution as the "better", more useful, more general pattern.See I set variables in a loop that's in a pipeline. Why do they disappear... (from Greg's Bash FAQ) for a detailed discussion on this topic.
Additional References & Sources:
Gnu Bash Manual, Pattern Matching
Filenames and Pathnames in Shell: How to do it Correctly, David A. Wheeler
Why you don't read lines with "for", Greg's Wiki
Why you shouldn't parse the output of ls(1), Greg's Wiki
Gnu Bash Manual, Process Substitution
(Updated to include #Socowi's execellent speed improvement)
With any $SHELL that supports it (dash/zsh/bash...):
find . -name "*.txt" -exec $SHELL -c '
for i in "$#" ; do
echo "$i"
done
' {} +
Done.
Original answer (shorter, but slower):
find . -name "*.txt" -exec $SHELL -c '
echo "$0"
' {} \;
If you can assume the file names don't contain newlines, you can read the output of find into a Bash array using the following command:
readarray -t x < <(find . -name '*.txt')
Note:
-t causes readarray to strip newlines.
It won't work if readarray is in a pipe, hence the process substitution.
readarray is available since Bash 4.
Bash 4.4 and up also supports the -d parameter for specifying the delimiter. Using the null character, instead of newline, to delimit the file names works also in the rare case that the file names contain newlines:
readarray -d '' x < <(find . -name '*.txt' -print0)
readarray can also be invoked as mapfile with the same options.
Reference: https://mywiki.wooledge.org/BashFAQ/005#Loading_lines_from_a_file_or_stream
# Doesn't handle whitespace
for x in `find . -name "*.txt" -print`; do
process_one $x
done
or
# Handles whitespace and newlines
find . -name "*.txt" -print0 | xargs -0 -n 1 process_one
I like to use find which is first assigned to variable and IFS switched to new line as follow:
FilesFound=$(find . -name "*.txt")
IFSbkp="$IFS"
IFS=$'\n'
counter=1;
for file in $FilesFound; do
echo "${counter}: ${file}"
let counter++;
done
IFS="$IFSbkp"
As commented by #Konrad Rudolph this will not work with "new lines" in file name. I still think it is handy as it covers most of the cases when you need to loop over command output.
As already posted on the top answer by Kevin, the best solution is to use a for loop with bash glob, but as bash glob is not recursive by default, this can be fixed by a bash recursive function:
#!/bin/bash
set -x
set -eu -o pipefail
all_files=();
function get_all_the_files()
{
directory="$1";
for item in "$directory"/* "$directory"/.[^.]*;
do
if [[ -d "$item" ]];
then
get_all_the_files "$item";
else
all_files+=("$item");
fi;
done;
}
get_all_the_files "/tmp";
for file_path in "${all_files[#]}"
do
printf 'My file is "%s"\n' "$file_path";
done;
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How can I creates array that contains the names of all the files in a folder?
How to get the list of files in a directory in a shell script?
based on other answers and comment of #phk, using fd #3:
(which still allows to use stdin inside the loop)
while IFS= read -r f <&3; do
echo "$f"
done 3< <(find . -iname "*filename*")
You can put the filenames returned by find into an array like this:
array=()
while IFS= read -r -d ''; do
array+=("$REPLY")
done < <(find . -name '*.txt' -print0)
Now you can just loop through the array to access individual items and do whatever you want with them.
Note: It's white space safe.
I think using this piece of code (piping the command after while done):
while read fname; do
echo "$fname"
done <<< "$(find . -name "*.txt")"
is better than this answer because while loop is executed in a subshell according to here, if you use this answer and variable changes cannot be seen after while loop if you want to modify variables inside the loop.
You can store your find output in array if you wish to use the output later as:
array=($(find . -name "*.txt"))
Now to print the each element in new line, you can either use for loop iterating to all the elements of array, or you can use printf statement.
for i in ${array[#]};do echo $i; done
or
printf '%s\n' "${array[#]}"
You can also use:
for file in "`find . -name "*.txt"`"; do echo "$file"; done
This will print each filename in newline
To only print the find output in list form, you can use either of the following:
find . -name "*.txt" -print 2>/dev/null
or
find . -name "*.txt" -print | grep -v 'Permission denied'
This will remove error messages and only give the filename as output in new line.
If you wish to do something with the filenames, storing it in array is good, else there is no need to consume that space and you can directly print the output from find.
function loop_through(){
length_="$(find . -name '*.txt' | wc -l)"
length_="${length_#"${length_%%[![:space:]]*}"}"
length_="${length_%"${length_##*[![:space:]]}"}"
for i in {1..$length_}
do
x=$(find . -name '*.txt' | sort | head -$i | tail -1)
echo $x
done
}
To grab the length of the list of files for loop, I used the first command "wc -l".
That command is set to a variable.
Then, I need to remove the trailing white spaces from the variable so the for loop can read it.
find <path> -xdev -type f -name *.txt -exec ls -l {} \;
This will list the files and give details about attributes.
Another alternative is to not use bash, but call Python to do the heavy lifting. I recurred to this because bash solutions as my other answer were too slow.
With this solution, we build a bash array of files from inline Python script:
#!/bin/bash
set -eu -o pipefail
dsep=":" # directory_separator
base_directory=/tmp
all_files=()
all_files_string="$(python3 -c '#!/usr/bin/env python3
import os
import sys
dsep="'"$dsep"'"
base_directory="'"$base_directory"'"
def log(*args, **kwargs):
print(*args, file=sys.stderr, **kwargs)
def check_invalid_characther(file_path):
for thing in ("\\", "\n"):
if thing in file_path:
raise RuntimeError(f"It is not allowed {thing} on \"{file_path}\"!")
def absolute_path_to_relative(base_directory, file_path):
relative_path = os.path.commonprefix( [ base_directory, file_path ] )
relative_path = os.path.normpath( file_path.replace( relative_path, "" ) )
# if you use Windows Python, it accepts / instead of \\
# if you have \ on your files names, rename them or comment this
relative_path = relative_path.replace("\\", "/")
if relative_path.startswith( "/" ):
relative_path = relative_path[1:]
return relative_path
for directory, directories, files in os.walk(base_directory):
for file in files:
local_file_path = os.path.join(directory, file)
local_file_name = absolute_path_to_relative(base_directory, local_file_path)
log(f"local_file_name {local_file_name}.")
check_invalid_characther(local_file_name)
print(f"{base_directory}{dsep}{local_file_name}")
' | dos2unix)";
if [[ -n "$all_files_string" ]];
then
readarray -t temp <<< "$all_files_string";
all_files+=("${temp[#]}");
fi;
for item in "${all_files[#]}";
do
OLD_IFS="$IFS"; IFS="$dsep";
read -r base_directory local_file_name <<< "$item"; IFS="$OLD_IFS";
printf 'item "%s", base_directory "%s", local_file_name "%s".\n' \
"$item" \
"$base_directory" \
"$local_file_name";
done;
Related:
os.walk without hidden folders
How to do a recursive sub-folder search and return files in a list?
How to split a string into an array in Bash?
How about if you use grep instead of find?
ls | grep .txt$ > out.txt
Now you can read this file and the filenames are in the form of a list.