How to loop through file names returned by find

Question

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

User · Answer

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

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TL DR  If you re just here for the most correct answer  you probably want my personal preference  find   -name    txt  -exec process        see the bottom of this post   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  lt  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

User · Answer

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

User · Answer

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  lt   lt  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  lt   lt  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

User · Answer

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  lt  amp 3  do     echo   f   done 3 lt   lt  find   -iname   filename

User · Answer

find  lt path gt  -xdev -type f -name   txt -exec ls -l        This will list the files and give details about attributes

User · Answer

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

User · Answer

You can put the filenames returned by find into an array like this   array    while IFS   read -r -d     do     array     REPLY   done  lt   lt  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

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How about if you use grep instead of find   ls   grep  txt   gt  out txt   Now you can read this file and the filenames are in the form of a list

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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  quot   txt quot   from the question is not recommended at all  If find gets a filename with spaces e g   quot the file txt quot  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  amp  filename expansion  for file in     txt  do          -e  file     amp  amp  continue    continue  if file does not exist       single filename is in  file     echo  quot  file quot        your code here done  2  Use find-read-while  amp  process substitution while IFS  read -r -d    file  do       single filename is in  file     echo  quot  file quot        your code here done  lt   lt  find   -name  quot   txt quot  -print0   Remarks on Pattern 1   bash returns the search pattern   quot   txt quot   if no matching file is found - so the extra line  quot continue  if file does not exist quot  is needed  see Bash Manual  Filename Expansion shell option nullglob can be used to avoid this extra line   quot If the failglob shell option is set  and no matches are found  an error message is printed and the command is not executed  quot   from Bash Manual above  shell option globstar   quot 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  quot  see Bash Manual  Shopt Builtin other options for filename expansion  extglob  nocaseglob  dotglob  amp  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  amp  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  quot   txt quot  -print0       while IFS  read -r -d    file  do          single filename in  file        echo  quot  file quot         files found 0     not working example          your code here    done     files found -eq 0     amp  amp  echo  quot files found quot     echo  quot no files found quot    When you try this piece of code  you will see  that it does not work  files found is always  quot true quot   amp  the code will always echo  quot no files found quot   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  quot better quot   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  amp  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  quot for quot   Greg s Wiki  Why you shouldn t parse the output of ls 1   Greg s Wiki  Gnu Bash Manual  Process Substitution

User · Answer

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 gt  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

User · Answer

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

User · Answer

I like to use find which is first assigned to variable and IFS switched to new line as follow  FilesFound   find   -name  quot   txt quot    IFSbkp  quot  IFS quot  IFS    n  counter 1  for file in  FilesFound  do     echo  quot   counter     file  quot      let counter    done IFS  quot  IFSbkp quot   As commented by  Konrad Rudolph this will not work with  quot new lines quot  in file name  I still think it is handy as it covers most of the cases when you need to loop over command output

[bash] How to loop through file names returned by find?

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