I have a folder, e.g. named 'folder'. There are 50000 txt files under it, e.g, '00001.txt, 00002.txt, etc'.
Now I want to use one command line to show the head 10 lines in '00001.txt'. I have tried:
ls folder | head -1
which will show the filename of the first:
00001.txt
But I want to show the contents of folder/00001.txt
So, how do I do something like os.path.join(folder, xx) and show its head -10?
The better way to do this is not to use ls at all; see Why you shouldn't parse the output of ls, and the corresponding UNIX & Linux question Why not parse ls (and what to do instead?).
On a shell with arrays, you can glob into an array, and refer to items it contains by index.
#!/usr/bin/env bash
# ^^^^- bash, NOT sh; sh does not support arrays
# make array files contain entries like folder/0001.txt, folder/0002.txt, etc
files=( folder/* ) # note: if no files found, it will be files=( "folder/*" )
# make sure the first item in that array exists; if it does't, that means
# the glob failed to expand because no files matching the string exist.
if [[ -e ${files[0]} || -L ${files[0]} ]]; then
# file exists; pass the name to head
head -n 10 <"${files[0]}"
else
# file does not exist; spit out an error
echo "No files found in folder/" >&2
fi
If you wanted more control, I'd probably use find. For example, to skip directories, the -type f predicate can be used (with -maxdepth 1 to turn off recursion):
IFS= read -r -d '' file < <(find folder -maxdepth 1 -type f -print0 | sort -z)
head -10 -- "$file"
Although hard to understand what you are asking but I think something like this will work:
head -10 $(ls | head -1)
Basically, you get the file from $(ls | head -1) and then print the content.
If you invoke the ls command as ls "$PWD"/folder, it will include the absolute path of the file in the output.
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.
#!/bin/bash
outbound=/home/user/outbound/
putfile=DATA_FILE_PUT_*.CSV
cd $outbound
filecnt=0
for file in $putfile; do let filecnt=filecnt+1; done
echo "Filecount: " $filecnt
So this code works well when there are files located in the outbound directory. I can place files into the outbound path and as long as they match the putfile mask then the files are incremented as expected.
Where the problem comes in is if I run this while there are no files located in $outbound.
If there are zero files there $filecnt still returns a 1 but I'm looking to have it return a 0 if there are no files there.
Am I missing something simple?
Put set -x just below the #! line to watch what your script is doing.
If there is no matching file, then the wildcard is left unexpanded, and the loop runs once, with file having the value DATA_FILE_PUT_*.CSV.
To change that, set the nullglob option. Note that this only works in bash, not in sh.
shopt -s nullglob
putfile=DATA_FILE_PUT_*.CSV
for file in $putfile; do let filecnt=filecnt+1; done
Note that the putfile variable contains the wildcard pattern, not the list of file names. It might make more sense to put the list of matches in a variable instead. This needs to be an array variable, and you need to change the current directory first. The number of matching files is then the length of the array.
#!/bin/bash
shopt -s nullglob
outbound=/home/user/outbound/
cd "$outbound"
putfiles=(DATA_FILE_PUT_*.CSV)
echo "Filecount: " ${#putfiles}
If you need to iterate over the files, take care to protect the expansion of the array with double quotes, otherwise if a file name contains whitespace then it will be split over several words (and if a filename contains wildcard characters, they will be expanded).
#!/bin/bash
shopt -s nullglob
outbound=/home/user/outbound/
cd "$outbound"
putfiles=(DATA_FILE_PUT_*.CSV)
for file in "${putfiles[#]}"; do
echo "Processing $file"
done
You could test if file exists first
for file in $putfile; do
if [ -f "$file" ] ; then
let filecnt=filecnt+1
fi
done
Or look for your files with find
for file in $(find . -type f -name="$putfile"); do
let filecnt=filecnt+1
done
or simply (fixed)
filecnt=$(find . -type f -name "$putfile" | wc -l); echo $filecnt
This is because when no matches are found, bash by default expands the wildcard DATA_FILE_PUT_*.CSV to the word DATA_FILE_PUT_*.CSV and therefore you end up with a count of 1.
To disable this behavior, use shopt -s nullglob
Not sure why you need a piece of code here. Following one liner should do your job.
ls ${outbound}/${putfile} | wc -l
Or
find ${outbound} -maxdepth 1 -type f -name "${putfile}" | wc -l
Using bash, how can one get the number of files in a folder, excluding directories from a shell script without the interpreter complaining?
With the help of a friend, I've tried
$files=$(find ../ -maxdepth 1 -type f | sort -n)
$num=$("ls -l" | "grep ^-" | "wc -l")
which returns from the command line:
../1-prefix_blended_fused.jpg: No such file or directory
ls -l : command not found
grep ^-: command not found
wc -l: command not found
respectively. These commands work on the command line, but NOT with a bash script.
Given a file filled with image files formatted like 1-pano.jpg, I want to grab all the images in the directory to get the largest numbered file to tack onto the next image being processed.
Why the discrepancy?
The quotes are causing the error messages.
To get a count of files in the directory:
shopt -s nullglob
numfiles=(*)
numfiles=${#numfiles[#]}
which creates an array and then replaces it with the count of its elements. This will include files and directories, but not dotfiles or . or .. or other dotted directories.
Use nullglob so an empty directory gives a count of 0 instead of 1.
You can instead use find -type f or you can count the directories and subtract:
# continuing from above
numdirs=(*/)
numdirs=${#numdirs[#]}
(( numfiles -= numdirs ))
Also see "How can I find the latest (newest, earliest, oldest) file in a directory?"
You can have as many spaces as you want inside an execution block. They often aid in readability. The only downside is that they make the file a little larger and may slow initial parsing (only) slightly. There are a few places that must have spaces (e.g. around [, [[, ], ]] and = in comparisons) and a few that must not (e.g. around = in an assignment.
ls -l | grep -v ^d | wc -l
One line.
How about:
count=$(find .. -maxdepth 1 -type f|wc -l)
echo $count
let count=count+1 # Increase by one, for the next file number
echo $count
Note that this solution is not efficient: it spawns sub shells for the find and wc commands, but it should work.
file_num=$(ls -1 --file-type | grep -v '/$' | wc -l)
this is a bit lightweight than a find command, and count all files of the current directory.
The most straightforward, reliable way I can think of is using the find command to create a reliably countable output.
Counting characters output of find with wc:
find . -maxdepth 1 -type f -printf '.' | wc --char
or string length of the find output:
a=$(find . -maxdepth 1 -type f -printf '.')
echo ${#a}
or using find output to populate an arithmetic expression:
echo $(($(find . -maxdepth 1 -type f -printf '+1')))
Simple efficient method:
#!/bin/bash
RES=$(find ${SOURCE} -type f | wc -l)
Get rid of the quotes. The shell is treating them like one file, so it's looking for "ls -l".
REmove the qoutes and you will be fine
Expanding on the accepted answer (by Dennis W): when I tried this approach I got incorrect counts for dirs without subdirs in Bash 4.4.5.
The issue is that by default nullglob is not set in Bash and numdirs=(*/) sets an 1 element array with the glob pattern */. Likewise I suspect numfiles=(*) would have 1 element for an empty folder.
Setting shopt -s nullglob to disable nullglobbing resolves the issue for me. For an excellent discussion on why nullglob is not set by default on Bash see the answer here: Why is nullglob not default?
Note: I would have commented on the answer directly but lack the reputation points.
Here's one way you could do it as a function. Note: you can pass this example, dirs for (directory count), files for files count or "all" for count of everything in a directory. Does not traverse tree as we aren't looking to do that.
function get_counts_dir() {
# -- handle inputs (e.g. get_counts_dir "files" /path/to/folder)
[[ -z "${1,,}" ]] && type="files" || type="${1,,}"
[[ -z "${2,,}" ]] && dir="$(pwd)" || dir="${2,,}"
shopt -s nullglob
PWD=$(pwd)
cd ${dir}
numfiles=(*)
numfiles=${#numfiles[#]}
numdirs=(*/)
numdirs=${#numdirs[#]}
# -- handle input types files/dirs/or both
result=0
case "${type,,}" in
"files")
result=$((( numfiles -= numdirs )))
;;
"dirs")
result=${numdirs}
;;
*) # -- returns all files/dirs
result=${numfiles}
;;
esac
cd ${PWD}
shopt -u nullglob
# -- return result --
[[ -z ${result} ]] && echo 0 || echo ${result}
}
Examples of using the function :
folder="/home"
get_counts_dir "files" "${folder}"
get_counts_dir "dirs" "${folder}"
get_counts_dir "both" "${folder}"
Will print something like :
2
4
6
Short and sweet method which also ignores symlinked directories.
count=$(ls -l | grep ^- | wc -l)
or if you have a target:
count=$(ls -l /path/to/target | grep ^- | wc -l)
This is my first Bash script so forgive me if this question is trivial. I need to count the number of files within a specified directory $HOME/.junk. I thought this would be simple and assumed the following would work:
numfiles= find $HOME/.junk -type f | wc -l
echo "There are $numfiles files in the .junk directory."
Typing find $HOME/.junk -type f | wc -l at the command line works exactly how I expected it to, simply returning the number of files. Why is this not working when it is entered within my script? Am I missing some special notation when it comes to passing options to the utilities?
Thank you very much for your time and help.
You just need to surround it with backticks:
numfiles=`find $HOME/.junk -type f | wc -l`
The term for this is command substitution.
if you are using bash you can also use $() for command substitution, like so:
numfiles=$(find $HOME/.junk -type f | wc -l)
I find this to be slightly more readable than backquotes, as well as having the ability to nest several commands inside one another.
with bash 4 (if you want recursive)
#!/bin/bash
shopt -s globstar
for file in **
do
((i++))
done
echo "total files: $i"
if not
#!/bin/bash
shopt -s dotglob
shopt -s nullglob
for file in *
do
((i++))
done
echo "total files: $i"