Related
Here is my code:
ls | grep -E '^application--[0-9]{4}-[0-9]{2}.tar.gz$' | awk '{if($1<"application--'"${CLEAR_DATE_LEVEL0}"'.tar.gz") print $1}' | xargs -r echo
ls | grep -E '^application--[0-9]{4}-[0-9]{2}.tar.gz$' | awk '{if($1<"application--'"${CLEAR_DATE_LEVEL0}"'.tar.gz") print $1}' | xargs -r rm
As you can see it will get a list of files, show it on screen (for logging purpose) and then delete it.
The issue is that if a file was created between first and second line gets executed, I will delete a file without logging that fact.
Is there a way to create a script that will read the same pipe twice, so the awk result will be piped to both xargs echo and xargs rm commands?
I know I can use a file as a temporary buffer, but I would like to avoid that.
You can change your command to something like
touch example
ls example* | tee >(xargs rm)
I would prefer to avoid parsing ls:
while IFS= read -r file; do
if [[ "$1" < "application--${CLEAR_DATE_LEVEL0}.tar.gz" ]]; then
echo "Removing ${file}"
rm "${file}"
fi
done < <(find . -regextype egrep -regex "./application--[0-9]{4}-[0-9]{2}.tar.gz")
EDIT: An improvement:
As #tripleee mentioned is their answer, using rm -v avoids the additional echo and will also avoid an echo when removing a file failed.
For your specific case, you don't need to read the pipe twice, you can just use rm -v to have rm itself also "echo" each file.
Also, in cases like this, it is better for shell scripts to use globs instead grep ..., both for robustness and performance reasons.
And once you do that, even better: you can loop on the glob and not go through any pipes at all (even more robust in the general case, because there are even less places to worry "could a character in this be special to that program?", and might perform better because everything stays in one process):
for file in application--[0-9][0-9][0-9][0-9]-[0-9][0-9].tar.gz
do
if [[ "$file" < "application--${CLEAR_DATE_LEVEL0}.tar.gz" ]]
then
# echo "$file"
# rm "$file"
rm -v "$file"
fi
done
But if you find yourself in a situation where you really do need to get data from a pipe and a glob won't work, there are a couple ways:
One neat trick in the shell is that loops and other compound commands can be pipes - so a loop can read a pipe, and the inside of the loop can have all the commands you wanted to have read from the pipe:
ls ... | awk ... | while IFS="" read -r file
do
# echo "$file"
# rm "$file"
rm -v "$file"
done
(As a general best practice, you'd want to set IFS= to the empty string for the read command so that read doesn't split the input on characters like spaces, and give read the -r argument to tell it to not interpret special characters like backslashes. In your specific case it doesn't matter.)
But if a loop doesn't work for what you need, then in the general case, you can catch the result of a pipe in a shell variable:
pipe_contents="$(ls application--[0-9][0-9][0-9][0-9]-[0-9][0-9].tar.gz | awk '{if($1<"application--'"${CLEAR_DATE_LEVEL0}"'.tar.gz") print $1}')"
echo "$pipe_contents"
rm $pipe_contents
(This works fine unless your pipe output contains characters that would be special to the shell at the point that the pipe output has to be unquoted - in this case, it needs to be unquoted for the rm, because if it's quoted then the shell won't split the captured pipe output on whitespace, and rm will end up looking for one big file name that looks like the entire pipe output. Part of why looping on a glob is more robust is that it doesn't have these kinds of problems: the pipe combines all file names into one big text that needs to be re-split on whitespace. Luckily in your case, your file names don't have whitespace nor globbing characters, so leaving the pipe output unquoted ends up being fine.)
Also, since you're using bash and your pipe data is multiple separate things, you can use an array variable (bash extension, also found in shells like zsh) instead of a regular variable:
files=($(ls application--[0-9][0-9][0-9][0-9]-[0-9][0-9].tar.gz | awk '{if($1<"application--'"${CLEAR_DATE_LEVEL0}"'.tar.gz") print $1}'))
echo "${files[#]}"
rm "${files[#]}"
(Note that an unquoted expansion still happens with the array, it just happens when defining the array instead of when passing the pipe contents to rm. A small advantage is that if you had multiple commands which needed the unquoted contents, using an array does the splitting only once. A big advantage is that once you recognize array syntax, it does a better job of expressing your big-picture intent through the code itself.)
You can also use a temporary file instead of a shell variable, but you said you want to avoid that. I also prefer a variable when the data fits in memory because Linux/UNIX does not give shell scripts a reliable way to clean up external resources (you can use trap but for example traps can't run on uncatchable signals).
P.S. ideally, in the general habit, you should use printf '%s\n' "$foo" instead of echo "$foo", because echo has various special cases (and portability inconsistencies, but that doesn't matter as much if you always use bash until you need to care about portable sh). In modern featureful shells like bash, you can also use %q instead of %s in printf, which is great because for example printf '%q\n' "${files[#]}" will actually print each file with any special characters properly quoted or escaped, which can help with debugging if you ever are dealing with files that have special whitespace or globbing characters in them.
No, a pipe is a stream - once you read something from it, it is forever gone from the pipe.
A good general solution is to use a temporary file; this lets you rewind and replay it. Just take care to remove it when you're done.
temp=$(mktemp -t) || exit
trap 'rm -f "$temp"' ERR EXIT
cat >"$temp"
cat "$temp"
xargs rm <"$temp"
The ERR and EXIT pseudo-signals are Bash extensions. For POSIX portability, you need a somewhat more involved set of trap commands.
Properly speaking, mktemp should receive an argument which is used as a template for the temporary file's name, so that the user can see which temporary file belongs to which tool. For example, if this script was called rmsponge, you could use mktemp rmspongeXXXXXXXXX to have mktemp generate a temporary file name which begins with rmsponge.
If you only expect a limited amount of input, perhaps just capture the input in a variable. However, this scales poorly, and could have rather unfortunate problems if the input data exceeds available memory;
# XXX avoid: scales poorly
values=$(cat)
xargs printf "%s\n" <<<"$values"
xargs rm <<<"$values"
The <<< "here string" syntax is also a Bash extension. This also suffers from the various issues from https://mywiki.wooledge.org/BashFAQ/020 but this is inherent to your problem articulation.
Of course, in this individual case, just use rm -v to see which files rm removes.
i trying to make a script to organize a pair of list i have, and process with other programs, but im a little bit stuck now.
I want from a List in Txt process every line first creating a folder to each line in the list and then process due to different scripts i have.
But my problem is is the list i give to the script is like 3-4 elements works great and create there own directory, but if i put a list with +1000 lines, then my script process only a few elements thru the scripts.
EDIT: the process are like 30-35 scripts, different language python,bash,python and golang
Any suggestions?
cat $STORES+NEW.txt | while read NEWSTORES
do
cd $STORES && mkdir $NEWSTORES && cd $NEWSTORES && mkdir .Files
python3 checkstatus.py -n $NEWSTORES
checkemployes $NEWSTORES -status
storemanagers -s $NEWSTORES -o $NEWSTORES+managers.txt
curl -s https://redacted.com/store?=$NEWSTORES | grep -vE "<|^[\*]*[\.]*$NEWSTORES" | sort -u | awk 'NF' > $NEWSTORES+site.txt
..
..
..
..
..
..
cd ../..
done
I'm not supposed to give an answer yet but I mistakenly answered my what should be a comment reply. Anyway here a few things I can suggest:
Avoid unnecessary use of cat.
Open your input file using another FD to prevent commands that read input inside the loop from eating the input: IFS= read -ru 3 NEWSTORES; do ...; done 3< "$STORES+NEW.txt" or { IFS= read -ru "$FD" NEWSTORES; do ...; done; } {FD}< "$STORES+NEW.txt". Also see https://stackoverflow.com/a/28837793/445221.
Not completely related but don't use while loop in a pipeline since it will execute in a subshell. In the future if you try to alter a variable and expect it to be saved outside the loop, it won't. You can use lastpipe to avoid it but it's unnecessary most of the time.
Place your variable expansions around double quotes to prevent unwanted word splitting and filename expansion.
Use -r option unless you want backslashes to escape characters.
Specify IFS= before read to prevent stripping of leading and trailing spaces.
Using readarray or mapfile makes it more convenient: readarray -t ALL_STORES_DATA < "$STORES+NEW.txt"; for NEWSTORES IN "${ALL_STORES_DATA[#]}"; do ...; done
Use lowercase characters on your variables when you don't use them in a global manner to avoid conflict with bash's variables.
I have a directory with about 2000 files. How can I select a random sample of N files through using either a bash script or a list of piped commands?
Here's a script that uses GNU sort's random option:
ls |sort -R |tail -$N |while read file; do
# Something involving $file, or you can leave
# off the while to just get the filenames
done
You can use shuf (from the GNU coreutils package) for that. Just feed it a list of file names and ask it to return the first line from a random permutation:
ls dirname | shuf -n 1
# probably faster and more flexible:
find dirname -type f | shuf -n 1
# etc..
Adjust the -n, --head-count=COUNT value to return the number of wanted lines. For example to return 5 random filenames you would use:
find dirname -type f | shuf -n 5
Here are a few possibilities that don't parse the output of ls and that are 100% safe regarding files with spaces and funny symbols in their name. All of them will populate an array randf with a list of random files. This array is easily printed with printf '%s\n' "${randf[#]}" if needed.
This one will possibly output the same file several times, and N needs to be known in advance. Here I chose N=42.
a=( * )
randf=( "${a[RANDOM%${#a[#]}]"{1..42}"}" )
This feature is not very well documented.
If N is not known in advance, but you really liked the previous possibility, you can use eval. But it's evil, and you must really make sure that N doesn't come directly from user input without being thoroughly checked!
N=42
a=( * )
eval randf=( \"\${a[RANDOM%\${#a[#]}]\"\{1..$N\}\"}\" )
I personally dislike eval and hence this answer!
The same using a more straightforward method (a loop):
N=42
a=( * )
randf=()
for((i=0;i<N;++i)); do
randf+=( "${a[RANDOM%${#a[#]}]}" )
done
If you don't want to possibly have several times the same file:
N=42
a=( * )
randf=()
for((i=0;i<N && ${#a[#]};++i)); do
((j=RANDOM%${#a[#]}))
randf+=( "${a[j]}" )
a=( "${a[#]:0:j}" "${a[#]:j+1}" )
done
Note. This is a late answer to an old post, but the accepted answer links to an external page that shows terrible bash practice, and the other answer is not much better as it also parses the output of ls. A comment to the accepted answer points to an excellent answer by Lhunath which obviously shows good practice, but doesn't exactly answer the OP.
ls | shuf -n 10 # ten random files
A simple solution for selecting 5 random files while avoiding to parse ls. It also works with files containing spaces, newlines and other special characters:
shuf -ezn 5 * | xargs -0 -n1 echo
Replace echo with the command you want to execute for your files.
This is an even later response to #gniourf_gniourf's late answer, which I just upvoted because it's by far the best answer, twice over. (Once for avoiding eval and once for safe filename handling.)
But it took me a few minutes to untangle the "not very well documented" feature(s) this answer uses. If your Bash skills are solid enough that you saw immediately how it works, then skip this comment. But I didn't, and having untangled it I think it's worth explaining.
Feature #1 is the shell's own file globbing. a=(*) creates an array, $a, whose members are the files in the current directory. Bash understands all the weirdnesses of filenames, so that list is guaranteed correct, guaranteed escaped, etc. No need to worry about properly parsing textual file names returned by ls.
Feature #2 is Bash parameter expansions for arrays, one nested within another. This starts with ${#ARRAY[#]}, which expands to the length of $ARRAY.
That expansion is then used to subscript the array. The standard way to find a random number between 1 and N is to take the value of random number modulo N. We want a random number between 0 and the length of our array. Here's the approach, broken into two lines for clarity's sake:
LENGTH=${#ARRAY[#]}
RANDOM=${a[RANDOM%$LENGTH]}
But this solution does it in a single line, removing the unnecessary variable assignment.
Feature #3 is Bash brace expansion, although I have to confess I don't entirely understand it. Brace expansion is used, for instance, to generate a list of 25 files named filename1.txt, filename2.txt, etc: echo "filename"{1..25}".txt".
The expression inside the subshell above, "${a[RANDOM%${#a[#]}]"{1..42}"}", uses that trick to produce 42 separate expansions. The brace expansion places a single digit in between the ] and the }, which at first I thought was subscripting the array, but if so it would be preceded by a colon. (It would also have returned 42 consecutive items from a random spot in the array, which is not at all the same thing as returning 42 random items from the array.) I think it's just making the shell run the expansion 42 times, thereby returning 42 random items from the array. (But if someone can explain it more fully, I'd love to hear it.)
The reason N has to be hardcoded (to 42) is that brace expansion happens before variable expansion.
Finally, here's Feature #4, if you want to do this recursively for a directory hierarchy:
shopt -s globstar
a=( ** )
This turns on a shell option that causes ** to match recursively. Now your $a array contains every file in the entire hierarchy.
If you have Python installed (works with either Python 2 or Python 3):
To select one file (or line from an arbitrary command), use
ls -1 | python -c "import sys; import random; print(random.choice(sys.stdin.readlines()).rstrip())"
To select N files/lines, use (note N is at the end of the command, replace this by a number)
ls -1 | python -c "import sys; import random; print(''.join(random.sample(sys.stdin.readlines(), int(sys.argv[1]))).rstrip())" N
If you want to copy a sample of those files to another folder:
ls | shuf -n 100 | xargs -I % cp % ../samples/
make samples directory first obviously.
MacOS does not have the sort -R and shuf commands, so I needed a bash only solution that randomizes all files without duplicates and did not find that here. This solution is similar to gniourf_gniourf's solution #4, but hopefully adds better comments.
The script should be easy to modify to stop after N samples using a counter with if, or gniourf_gniourf's for loop with N. $RANDOM is limited to ~32000 files, but that should do for most cases.
#!/bin/bash
array=(*) # this is the array of files to shuffle
# echo ${array[#]}
for dummy in "${array[#]}"; do # do loop length(array) times; once for each file
length=${#array[#]}
randomi=$(( $RANDOM % $length )) # select a random index
filename=${array[$randomi]}
echo "Processing: '$filename'" # do something with the file
unset -v "array[$randomi]" # set the element at index $randomi to NULL
array=("${array[#]}") # remove NULL elements introduced by unset; copy array
done
If you have more files in your folder, you can use the below piped command I found in unix stackexchange.
find /some/dir/ -type f -print0 | xargs -0 shuf -e -n 8 -z | xargs -0 cp -vt /target/dir/
Here I wanted to copy the files, but if you want to move files or do something else, just change the last command where I have used cp.
This is the only script I can get to play nice with bash on MacOS. I combined and edited snippets from the following two links:
ls command: how can I get a recursive full-path listing, one line per file?
http://www.linuxquestions.org/questions/linux-general-1/is-there-a-bash-command-for-picking-a-random-file-678687/
#!/bin/bash
# Reads a given directory and picks a random file.
# The directory you want to use. You could use "$1" instead if you
# wanted to parametrize it.
DIR="/path/to/"
# DIR="$1"
# Internal Field Separator set to newline, so file names with
# spaces do not break our script.
IFS='
'
if [[ -d "${DIR}" ]]
then
# Runs ls on the given dir, and dumps the output into a matrix,
# it uses the new lines character as a field delimiter, as explained above.
# file_matrix=($(ls -LR "${DIR}"))
file_matrix=($(ls -R $DIR | awk '; /:$/&&f{s=$0;f=0}; /:$/&&!f{sub(/:$/,"");s=$0;f=1;next}; NF&&f{ print s"/"$0 }'))
num_files=${#file_matrix[*]}
# This is the command you want to run on a random file.
# Change "ls -l" by anything you want, it's just an example.
ls -l "${file_matrix[$((RANDOM%num_files))]}"
fi
exit 0
I use this: it uses temporary file but goes deeply in a directory until it find a regular file and return it.
# find for a quasi-random file in a directory tree:
# directory to start search from:
ROOT="/";
tmp=/tmp/mytempfile
TARGET="$ROOT"
FILE="";
n=
r=
while [ -e "$TARGET" ]; do
TARGET="$(readlink -f "${TARGET}/$FILE")" ;
if [ -d "$TARGET" ]; then
ls -1 "$TARGET" 2> /dev/null > $tmp || break;
n=$(cat $tmp | wc -l);
if [ $n != 0 ]; then
FILE=$(shuf -n 1 $tmp)
# or if you dont have/want to use shuf:
# r=$(($RANDOM % $n)) ;
# FILE=$(tail -n +$(( $r + 1 )) $tmp | head -n 1);
fi ;
else
if [ -f "$TARGET" ] ; then
rm -f $tmp
echo $TARGET
break;
else
# is not a regular file, restart:
TARGET="$ROOT"
FILE=""
fi
fi
done;
How about a Perl solution slightly doctored from Mr. Kang over here:
How can I shuffle the lines of a text file on the Unix command line or in a shell script?
$ ls | perl -MList::Util=shuffle -e '#lines = shuffle(<>); print
#lines[0..4]'
Suppose I've got a list of files
file1
"file 1"
file2
a for...in loop breaks it up between whitespace, not newlines:
for x in $( ls ); do
echo $x
done
results:
file
1
file1
file2
I want to execute a command on each file. "file" and "1" above are not actual files. How can I do that if the filenames contains things like spaces or commas?
It's a little trickier than I think find -print0 | xargs -0 could handle, because I actually want the command to be something like "convert input/file1.jpg .... output/file1.jpg" so I need to permutate the filename in the process.
Actually, Mark's suggestion works fine without even doing anything to the internal field separator. The problem is running ls in a subshell, whether by backticks or $( ) causes the for loop to be unable to distinguish between spaces in names. Simply using
for f in *
instead of the ls solves the problem.
#!/bin/bash
for f in *
do
echo "$f"
done
UPDATE BY OP: this answer sucks and shouldn't be on top ... #Jordan's post below should be the accepted answer.
one possible way:
ls -1 | while read x; do
echo $x
done
I know this one is LONG past "answered", and with all due respect to eduffy, I came up with a better way and I thought I'd share it.
What's "wrong" with eduffy's answer isn't that it's wrong, but that it imposes what for me is a painful limitation: there's an implied creation of a subshell when the output of the ls is piped and this means that variables set inside the loop are lost after the loop exits. Thus, if you want to write some more sophisticated code, you have a pain in the buttocks to deal with.
My solution was to take the "readline" function and write a program out of it in which you can specify any specific line number that you may want that results from any given function call. ... As a simple example, starting with eduffy's:
ls_output=$(ls -1)
# The cut at the end of the following line removes any trailing new line character
declare -i line_count=$(echo "$ls_output" | wc -l | cut -d ' ' -f 1)
declare -i cur_line=1
while [ $cur_line -le $line_count ] ;
do
# NONE of the values in the variables inside this do loop are trapped here.
filename=$(echo "$ls_output" | readline -n $cur_line)
# Now line contains a filename from the preceeding ls command
cur_line=cur_line+1
done
Now you have wrapped up all the subshell activity into neat little contained packages and can go about your shell coding without having to worry about the scope of your variable values getting trapped in subshells.
I wrote my version of readline in gnuc if anyone wants a copy, it's a little big to post here, but maybe we can find a way...
Hope this helps,
RT
I have a directory with about 2000 files. How can I select a random sample of N files through using either a bash script or a list of piped commands?
Here's a script that uses GNU sort's random option:
ls |sort -R |tail -$N |while read file; do
# Something involving $file, or you can leave
# off the while to just get the filenames
done
You can use shuf (from the GNU coreutils package) for that. Just feed it a list of file names and ask it to return the first line from a random permutation:
ls dirname | shuf -n 1
# probably faster and more flexible:
find dirname -type f | shuf -n 1
# etc..
Adjust the -n, --head-count=COUNT value to return the number of wanted lines. For example to return 5 random filenames you would use:
find dirname -type f | shuf -n 5
Here are a few possibilities that don't parse the output of ls and that are 100% safe regarding files with spaces and funny symbols in their name. All of them will populate an array randf with a list of random files. This array is easily printed with printf '%s\n' "${randf[#]}" if needed.
This one will possibly output the same file several times, and N needs to be known in advance. Here I chose N=42.
a=( * )
randf=( "${a[RANDOM%${#a[#]}]"{1..42}"}" )
This feature is not very well documented.
If N is not known in advance, but you really liked the previous possibility, you can use eval. But it's evil, and you must really make sure that N doesn't come directly from user input without being thoroughly checked!
N=42
a=( * )
eval randf=( \"\${a[RANDOM%\${#a[#]}]\"\{1..$N\}\"}\" )
I personally dislike eval and hence this answer!
The same using a more straightforward method (a loop):
N=42
a=( * )
randf=()
for((i=0;i<N;++i)); do
randf+=( "${a[RANDOM%${#a[#]}]}" )
done
If you don't want to possibly have several times the same file:
N=42
a=( * )
randf=()
for((i=0;i<N && ${#a[#]};++i)); do
((j=RANDOM%${#a[#]}))
randf+=( "${a[j]}" )
a=( "${a[#]:0:j}" "${a[#]:j+1}" )
done
Note. This is a late answer to an old post, but the accepted answer links to an external page that shows terrible bash practice, and the other answer is not much better as it also parses the output of ls. A comment to the accepted answer points to an excellent answer by Lhunath which obviously shows good practice, but doesn't exactly answer the OP.
ls | shuf -n 10 # ten random files
A simple solution for selecting 5 random files while avoiding to parse ls. It also works with files containing spaces, newlines and other special characters:
shuf -ezn 5 * | xargs -0 -n1 echo
Replace echo with the command you want to execute for your files.
This is an even later response to #gniourf_gniourf's late answer, which I just upvoted because it's by far the best answer, twice over. (Once for avoiding eval and once for safe filename handling.)
But it took me a few minutes to untangle the "not very well documented" feature(s) this answer uses. If your Bash skills are solid enough that you saw immediately how it works, then skip this comment. But I didn't, and having untangled it I think it's worth explaining.
Feature #1 is the shell's own file globbing. a=(*) creates an array, $a, whose members are the files in the current directory. Bash understands all the weirdnesses of filenames, so that list is guaranteed correct, guaranteed escaped, etc. No need to worry about properly parsing textual file names returned by ls.
Feature #2 is Bash parameter expansions for arrays, one nested within another. This starts with ${#ARRAY[#]}, which expands to the length of $ARRAY.
That expansion is then used to subscript the array. The standard way to find a random number between 1 and N is to take the value of random number modulo N. We want a random number between 0 and the length of our array. Here's the approach, broken into two lines for clarity's sake:
LENGTH=${#ARRAY[#]}
RANDOM=${a[RANDOM%$LENGTH]}
But this solution does it in a single line, removing the unnecessary variable assignment.
Feature #3 is Bash brace expansion, although I have to confess I don't entirely understand it. Brace expansion is used, for instance, to generate a list of 25 files named filename1.txt, filename2.txt, etc: echo "filename"{1..25}".txt".
The expression inside the subshell above, "${a[RANDOM%${#a[#]}]"{1..42}"}", uses that trick to produce 42 separate expansions. The brace expansion places a single digit in between the ] and the }, which at first I thought was subscripting the array, but if so it would be preceded by a colon. (It would also have returned 42 consecutive items from a random spot in the array, which is not at all the same thing as returning 42 random items from the array.) I think it's just making the shell run the expansion 42 times, thereby returning 42 random items from the array. (But if someone can explain it more fully, I'd love to hear it.)
The reason N has to be hardcoded (to 42) is that brace expansion happens before variable expansion.
Finally, here's Feature #4, if you want to do this recursively for a directory hierarchy:
shopt -s globstar
a=( ** )
This turns on a shell option that causes ** to match recursively. Now your $a array contains every file in the entire hierarchy.
If you have Python installed (works with either Python 2 or Python 3):
To select one file (or line from an arbitrary command), use
ls -1 | python -c "import sys; import random; print(random.choice(sys.stdin.readlines()).rstrip())"
To select N files/lines, use (note N is at the end of the command, replace this by a number)
ls -1 | python -c "import sys; import random; print(''.join(random.sample(sys.stdin.readlines(), int(sys.argv[1]))).rstrip())" N
If you want to copy a sample of those files to another folder:
ls | shuf -n 100 | xargs -I % cp % ../samples/
make samples directory first obviously.
MacOS does not have the sort -R and shuf commands, so I needed a bash only solution that randomizes all files without duplicates and did not find that here. This solution is similar to gniourf_gniourf's solution #4, but hopefully adds better comments.
The script should be easy to modify to stop after N samples using a counter with if, or gniourf_gniourf's for loop with N. $RANDOM is limited to ~32000 files, but that should do for most cases.
#!/bin/bash
array=(*) # this is the array of files to shuffle
# echo ${array[#]}
for dummy in "${array[#]}"; do # do loop length(array) times; once for each file
length=${#array[#]}
randomi=$(( $RANDOM % $length )) # select a random index
filename=${array[$randomi]}
echo "Processing: '$filename'" # do something with the file
unset -v "array[$randomi]" # set the element at index $randomi to NULL
array=("${array[#]}") # remove NULL elements introduced by unset; copy array
done
If you have more files in your folder, you can use the below piped command I found in unix stackexchange.
find /some/dir/ -type f -print0 | xargs -0 shuf -e -n 8 -z | xargs -0 cp -vt /target/dir/
Here I wanted to copy the files, but if you want to move files or do something else, just change the last command where I have used cp.
This is the only script I can get to play nice with bash on MacOS. I combined and edited snippets from the following two links:
ls command: how can I get a recursive full-path listing, one line per file?
http://www.linuxquestions.org/questions/linux-general-1/is-there-a-bash-command-for-picking-a-random-file-678687/
#!/bin/bash
# Reads a given directory and picks a random file.
# The directory you want to use. You could use "$1" instead if you
# wanted to parametrize it.
DIR="/path/to/"
# DIR="$1"
# Internal Field Separator set to newline, so file names with
# spaces do not break our script.
IFS='
'
if [[ -d "${DIR}" ]]
then
# Runs ls on the given dir, and dumps the output into a matrix,
# it uses the new lines character as a field delimiter, as explained above.
# file_matrix=($(ls -LR "${DIR}"))
file_matrix=($(ls -R $DIR | awk '; /:$/&&f{s=$0;f=0}; /:$/&&!f{sub(/:$/,"");s=$0;f=1;next}; NF&&f{ print s"/"$0 }'))
num_files=${#file_matrix[*]}
# This is the command you want to run on a random file.
# Change "ls -l" by anything you want, it's just an example.
ls -l "${file_matrix[$((RANDOM%num_files))]}"
fi
exit 0
I use this: it uses temporary file but goes deeply in a directory until it find a regular file and return it.
# find for a quasi-random file in a directory tree:
# directory to start search from:
ROOT="/";
tmp=/tmp/mytempfile
TARGET="$ROOT"
FILE="";
n=
r=
while [ -e "$TARGET" ]; do
TARGET="$(readlink -f "${TARGET}/$FILE")" ;
if [ -d "$TARGET" ]; then
ls -1 "$TARGET" 2> /dev/null > $tmp || break;
n=$(cat $tmp | wc -l);
if [ $n != 0 ]; then
FILE=$(shuf -n 1 $tmp)
# or if you dont have/want to use shuf:
# r=$(($RANDOM % $n)) ;
# FILE=$(tail -n +$(( $r + 1 )) $tmp | head -n 1);
fi ;
else
if [ -f "$TARGET" ] ; then
rm -f $tmp
echo $TARGET
break;
else
# is not a regular file, restart:
TARGET="$ROOT"
FILE=""
fi
fi
done;
How about a Perl solution slightly doctored from Mr. Kang over here:
How can I shuffle the lines of a text file on the Unix command line or in a shell script?
$ ls | perl -MList::Util=shuffle -e '#lines = shuffle(<>); print
#lines[0..4]'