Make xargs execute the command once for each line of input

Question

How can I make xargs execute the command exactly once for each line of input given  It s default behavior is to chunk the lines and execute the command once  passing multiple lines to each instance       From http   en wikipedia org wiki Xargs        find  path -type f -print0   xargs -0 rm      In this example  find feeds the input of xargs with a long list of file names  xargs then splits this list into sublists and calls rm once for every sublist  This is more efficient than this functionally equivalent version       find  path -type f -exec rm           I know that find has the  exec  flag   I am just quoting an illustrative example from another resource

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execute ant task clean-all on every build xml on current or sub-folder   find   -name  build xml  -exec ant -f    clean-all

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In your example  the point of piping the output of find to xargs is that the standard behavior of find s -exec option is to execute the command once for each found file  If you re using find  and you want its standard behavior  then the answer is simple - don t use xargs to begin with

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You can limit the number of lines  or arguments  if there are spaces between each argument  using the --max-lines or --max-args flags  respectively     -L max-lines          Use at most max-lines nonblank input lines per command line   Trailing blanks cause an input line to be logically continued on the next  input          line   Implies -x     --max-lines  max-lines   -l max-lines           Synonym  for  the -L option   Unlike -L  the max-lines argument is optional   If max-args is not specified  it defaults to one   The -l option          is deprecated since the POSIX standard specifies -L instead     --max-args max-args  -n max-args          Use at most max-args arguments per command line   Fewer than max-args arguments will be used if the size  see  the  -s  option   is  exceeded           unless the -x option is given  in which case xargs will exit

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In your example  the point of piping the output of find to xargs is that the standard behavior of find s -exec option is to execute the command once for each found file  If you re using find  and you want its standard behavior  then the answer is simple - don t use xargs to begin with

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How can I make xargs execute the command exactly once for each line of input given    -L 1 is the simple solution but it does not work if any of the files contain spaces in them   This is a key function of find s -print0 argument     to separate the arguments by   0  character instead of whitespace   Here s an example   echo  file with space txt    xargs -L 1 ls ls  file  No such file or directory ls  with  No such file or directory ls  space txt  No such file or directory   A better solution is to use tr to convert newlines to null   0  characters  and then use the xargs -0 argument   Here s an example   echo  file with space txt    tr   n    0    xargs -0 ls file with space txt   If you then need to limit the number of calls you can use the -n 1 argument to make one call to the program for each input   echo  file with space txt    tr   n    0    xargs -0 -n 1 ls   This also allows you to filter the output of find before converting the breaks into nulls   find   -name    xml   grep -v  target    tr   n    0    xargs -0 tar -cf xml tar

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The following will only work if you do not have spaces in your input   xargs -L 1 xargs --max-lines 1   synonym for the -L option    from the man page   -L max-lines           Use at most max-lines nonblank input lines per command line            Trailing blanks cause an input line to be logically continued  on           the next input line   Implies -x

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How can I make xargs execute the command exactly once for each line of input given    -L 1 is the simple solution but it does not work if any of the files contain spaces in them   This is a key function of find s -print0 argument     to separate the arguments by   0  character instead of whitespace   Here s an example   echo  file with space txt    xargs -L 1 ls ls  file  No such file or directory ls  with  No such file or directory ls  space txt  No such file or directory   A better solution is to use tr to convert newlines to null   0  characters  and then use the xargs -0 argument   Here s an example   echo  file with space txt    tr   n    0    xargs -0 ls file with space txt   If you then need to limit the number of calls you can use the -n 1 argument to make one call to the program for each input   echo  file with space txt    tr   n    0    xargs -0 -n 1 ls   This also allows you to filter the output of find before converting the breaks into nulls   find   -name    xml   grep -v  target    tr   n    0    xargs -0 tar -cf xml tar

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execute ant task clean-all on every build xml on current or sub-folder   find   -name  build xml  -exec ant -f    clean-all

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If you want to run the command for every line  i e  result  coming from find  then what do you need the xargs for   Try   find path -type f -exec your-command        where the literal    gets substituted by the filename and the literal    is needed for find to know that the custom command ends there   EDIT    after the edit of your question clarifying that you know about -exec   From man xargs      -L max-lines    Use at most max-lines nonblank input lines per command line   Trailing    blanks cause an input line to be logically continued on the next input line     Implies -x    Note that filenames ending in blanks would cause you trouble if you use xargs     mkdir  tmp bax  cd  tmp bax   touch a   b c   c   find   -type f -print   xargs -L1 wc -l 0   c 0   c 0 total 0   b wc    a  No such file or directory   So if you don t care about the -exec option  you better use -print0 and -0     find   -type f -print0   xargs -0L1 wc -l 0   c 0   c 0   b 0   a

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You can limit the number of lines  or arguments  if there are spaces between each argument  using the --max-lines or --max-args flags  respectively     -L max-lines          Use at most max-lines nonblank input lines per command line   Trailing blanks cause an input line to be logically continued on the next  input          line   Implies -x     --max-lines  max-lines   -l max-lines           Synonym  for  the -L option   Unlike -L  the max-lines argument is optional   If max-args is not specified  it defaults to one   The -l option          is deprecated since the POSIX standard specifies -L instead     --max-args max-args  -n max-args          Use at most max-args arguments per command line   Fewer than max-args arguments will be used if the size  see  the  -s  option   is  exceeded           unless the -x option is given  in which case xargs will exit

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If you want to run the command for every line  i e  result  coming from find  then what do you need the xargs for   Try   find path -type f -exec your-command        where the literal    gets substituted by the filename and the literal    is needed for find to know that the custom command ends there   EDIT    after the edit of your question clarifying that you know about -exec   From man xargs      -L max-lines    Use at most max-lines nonblank input lines per command line   Trailing    blanks cause an input line to be logically continued on the next input line     Implies -x    Note that filenames ending in blanks would cause you trouble if you use xargs     mkdir  tmp bax  cd  tmp bax   touch a   b c   c   find   -type f -print   xargs -L1 wc -l 0   c 0   c 0 total 0   b wc    a  No such file or directory   So if you don t care about the -exec option  you better use -print0 and -0     find   -type f -print0   xargs -0L1 wc -l 0   c 0   c 0   b 0   a

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Another alternative     find  path -type f   while read ln  do echo  processing  ln   done

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The following will only work if you do not have spaces in your input   xargs -L 1 xargs --max-lines 1   synonym for the -L option    from the man page   -L max-lines           Use at most max-lines nonblank input lines per command line            Trailing blanks cause an input line to be logically continued  on           the next input line   Implies -x

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You can limit the number of lines  or arguments  if there are spaces between each argument  using the --max-lines or --max-args flags  respectively     -L max-lines          Use at most max-lines nonblank input lines per command line   Trailing blanks cause an input line to be logically continued on the next  input          line   Implies -x     --max-lines  max-lines   -l max-lines           Synonym  for  the -L option   Unlike -L  the max-lines argument is optional   If max-args is not specified  it defaults to one   The -l option          is deprecated since the POSIX standard specifies -L instead     --max-args max-args  -n max-args          Use at most max-args arguments per command line   Fewer than max-args arguments will be used if the size  see  the  -s  option   is  exceeded           unless the -x option is given  in which case xargs will exit

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It seems I don t have enough reputation to add a comment to Tobia s answer above  so I am adding this  answer  to help those of us wanting to experiment with xargs the same way on the Windows platforms   Here is a windows batch file that does the same thing as Tobia s quickly coded  show  script    echo off REM REM  cool trick of using  set  to echo without new line REM   from   http   www psteiner com 2012 05 windows-batch-echo-without-new-line html  REM if    1              exit  b     lt nul set  p Args      1  shift   start if not    1               lt nul set  p      1      shift     goto start   echo

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find path -type f   xargs -L1 command    is all you need

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If you want to run the command for every line  i e  result  coming from find  then what do you need the xargs for   Try   find path -type f -exec your-command        where the literal    gets substituted by the filename and the literal    is needed for find to know that the custom command ends there   EDIT    after the edit of your question clarifying that you know about -exec   From man xargs      -L max-lines    Use at most max-lines nonblank input lines per command line   Trailing    blanks cause an input line to be logically continued on the next input line     Implies -x    Note that filenames ending in blanks would cause you trouble if you use xargs     mkdir  tmp bax  cd  tmp bax   touch a   b c   c   find   -type f -print   xargs -L1 wc -l 0   c 0   c 0 total 0   b wc    a  No such file or directory   So if you don t care about the -exec option  you better use -print0 and -0     find   -type f -print0   xargs -0L1 wc -l 0   c 0   c 0   b 0   a

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Draemon answers seems to be right with  -0  even with space in the file   I was trying the xargs command and I found that  -0  works perfectly with  -L   even the spaces are treated  if input was null terminated    the following is an example     touch  file with space   touch  file1   touch  file2    The following will split the nulls and execute the command on each argument in the list      find   -name  file   -print0   xargs -0 -L1   file with space   file1   file2   so -L1 will execute the argument on each null terminated character if used with  -0   To see the difference try      find   -name  file   -print0   xargs -0   xargs -L1    file with space   file1   file2   even this will execute once      find   -name  file   -print0    xargs -0    xargs -0 -L1   file with space   file1   file2   The command will execute once as the  -L  now doesn t split on null byte  you need to provide both  -0  and  -L  to work

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It seems I don t have enough reputation to add a comment to Tobia s answer above  so I am adding this  answer  to help those of us wanting to experiment with xargs the same way on the Windows platforms   Here is a windows batch file that does the same thing as Tobia s quickly coded  show  script    echo off REM REM  cool trick of using  set  to echo without new line REM   from   http   www psteiner com 2012 05 windows-batch-echo-without-new-line html  REM if    1              exit  b     lt nul set  p Args      1  shift   start if not    1               lt nul set  p      1      shift     goto start   echo

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In your example  the point of piping the output of find to xargs is that the standard behavior of find s -exec option is to execute the command once for each found file  If you re using find  and you want its standard behavior  then the answer is simple - don t use xargs to begin with

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These two ways also work  and will work for other commands that are not using find   xargs -I      rm      xargs -i rm        example use case   find   -name    pyc    xargs -i rm        will delete all pyc files under this directory even if the pyc files contain spaces

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Another alternative     find  path -type f   while read ln  do echo  processing  ln   done

User · Answer

find path -type f   xargs -L1 command    is all you need

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Draemon answers seems to be right with  -0  even with space in the file   I was trying the xargs command and I found that  -0  works perfectly with  -L   even the spaces are treated  if input was null terminated    the following is an example     touch  file with space   touch  file1   touch  file2    The following will split the nulls and execute the command on each argument in the list      find   -name  file   -print0   xargs -0 -L1   file with space   file1   file2   so -L1 will execute the argument on each null terminated character if used with  -0   To see the difference try      find   -name  file   -print0   xargs -0   xargs -L1    file with space   file1   file2   even this will execute once      find   -name  file   -print0    xargs -0    xargs -0 -L1   file with space   file1   file2   The command will execute once as the  -L  now doesn t split on null byte  you need to provide both  -0  and  -L  to work

User · Answer

find path -type f   xargs -L1 command    is all you need

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These two ways also work  and will work for other commands that are not using find   xargs -I      rm      xargs -i rm        example use case   find   -name    pyc    xargs -i rm        will delete all pyc files under this directory even if the pyc files contain spaces

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The following command will find all the files  -type f  in  path and then copy them using cp to the current folder   Note the use if -I   to specify a placeholder character in the cp command line so that arguments can be placed after the file name   find  path -type f -print0   xargs -0 -I   cp      Tested with xargs  GNU findutils  4 4 0

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It seems to me all existing answers on this page are wrong  including the one marked as correct  That stems from the fact that the question is ambiguously worded  Summary     If you want to execute the command  quot exactly once for each line of input  quot  passing the entire line  without newline  to the command as a single argument  then this is the best UNIX-compatible way to do it        tr   n    0    xargs -0 -n1      If you are using GNU xargs and don t need to be compatible with all other UNIX s  FreeBSD  Mac OS X  etc   then you can use the GNU-specific option -d        xargs -d  n -n1      Now for the long explanation     There are two issues to take into account when using xargs   how does it split the input into  quot arguments quot   and how many arguments to pass the child command at a time   To test xargs  behavior  we need an utility that shows how many times it s being executed and with how many arguments  I don t know if there is a standard utility to do that  but we can code it quite easily in bash     bin bash echo -n  quot - gt   quot   for a in  quot    quot   do echo -n  quot   quot  a  quot   quot   done  echo  Assuming you save it as show in your current directory and make it executable  here is how it works      show one two  three and four  - gt   quot one quot   quot two quot   quot three and four quot    Now  if the original question is really about point 2  above  as I think it is  after reading it a few times over  and it is to be read like this  changes in bold    How can I make xargs execute the command exactly once for each argument of input given  Its default behavior is to chunk the input into arguments and execute the command as few times as possible  passing multiple arguments to each instance   then the answer is -n 1  Let s compare xargs  default behavior  which splits the input around whitespace and calls the command as few times as possible    echo one two  three and four    xargs   show  - gt   quot one quot   quot two quot   quot three quot   quot and quot   quot four quot    and its behavior with -n 1    echo one two  three and four    xargs -n 1   show  - gt   quot one quot   - gt   quot two quot   - gt   quot three quot   - gt   quot and quot   - gt   quot four quot    If  on the other hand  the original question was about point 1  input splitting and it was to be read like this  many people coming here seem to think that s the case  or are confusing the two issues    How can I make xargs execute the command with exactly one argument for each line of input given  Its default behavior is to chunk the lines around whitespace   then the answer is more subtle  One would think that -L 1 could be of help  but it turns out it doesn t change argument parsing  It only executes the command once for each input line  with as many arguments as were there on that input line    echo   one ntwo nthree and four    xargs -L 1   show  - gt   quot one quot   - gt   quot two quot   - gt   quot three quot   quot and quot   quot four quot    Not only that  but if a line ends with whitespace  it is appended to the next    echo   one  ntwo nthree and four    xargs -L 1   show  - gt   quot one quot   quot two quot   - gt   quot three quot   quot and quot   quot four quot    Clearly  -L is not about changing the way xargs splits the input into arguments  The only argument that does so in a cross-platform fashion  excluding GNU extensions  is -0  which splits the input around NUL bytes  Then  it s just a matter of translating newlines to NUL with the help of tr    echo   one  ntwo nthree and four    tr   n    0    xargs -0   show  - gt   quot one  quot   quot two quot   quot three and four quot    Now the argument parsing looks all right  including the trailing whitespace  Finally  if you combine this technique with -n 1  you get exactly one command execution per input line  whatever input you have  which may be yet another way to look at the original question  possibly the most intuitive  given the title     echo   one  ntwo nthree and four    tr   n    0    xargs -0 -n1   show  - gt   quot one  quot   - gt   quot two quot   - gt   quot three and four quot    As mentioned above  if you are using GNU xargs you can replace the tr with the GNU-specific option -d    echo   one  ntwo nthree and four    xargs -d  n -n1   show  - gt   quot one  quot   - gt   quot two quot   - gt   quot three and four quot

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The following will only work if you do not have spaces in your input   xargs -L 1 xargs --max-lines 1   synonym for the -L option    from the man page   -L max-lines           Use at most max-lines nonblank input lines per command line            Trailing blanks cause an input line to be logically continued  on           the next input line   Implies -x

User · Answer

The following will only work if you do not have spaces in your input   xargs -L 1 xargs --max-lines 1   synonym for the -L option    from the man page   -L max-lines           Use at most max-lines nonblank input lines per command line            Trailing blanks cause an input line to be logically continued  on           the next input line   Implies -x

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find path -type f   xargs -L1 command    is all you need

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It seems to me all existing answers on this page are wrong  including the one marked as correct  That stems from the fact that the question is ambiguously worded  Summary     If you want to execute the command  quot exactly once for each line of input  quot  passing the entire line  without newline  to the command as a single argument  then this is the best UNIX-compatible way to do it        tr   n    0    xargs -0 -n1      If you are using GNU xargs and don t need to be compatible with all other UNIX s  FreeBSD  Mac OS X  etc   then you can use the GNU-specific option -d        xargs -d  n -n1      Now for the long explanation     There are two issues to take into account when using xargs   how does it split the input into  quot arguments quot   and how many arguments to pass the child command at a time   To test xargs  behavior  we need an utility that shows how many times it s being executed and with how many arguments  I don t know if there is a standard utility to do that  but we can code it quite easily in bash     bin bash echo -n  quot - gt   quot   for a in  quot    quot   do echo -n  quot   quot  a  quot   quot   done  echo  Assuming you save it as show in your current directory and make it executable  here is how it works      show one two  three and four  - gt   quot one quot   quot two quot   quot three and four quot    Now  if the original question is really about point 2  above  as I think it is  after reading it a few times over  and it is to be read like this  changes in bold    How can I make xargs execute the command exactly once for each argument of input given  Its default behavior is to chunk the input into arguments and execute the command as few times as possible  passing multiple arguments to each instance   then the answer is -n 1  Let s compare xargs  default behavior  which splits the input around whitespace and calls the command as few times as possible    echo one two  three and four    xargs   show  - gt   quot one quot   quot two quot   quot three quot   quot and quot   quot four quot    and its behavior with -n 1    echo one two  three and four    xargs -n 1   show  - gt   quot one quot   - gt   quot two quot   - gt   quot three quot   - gt   quot and quot   - gt   quot four quot    If  on the other hand  the original question was about point 1  input splitting and it was to be read like this  many people coming here seem to think that s the case  or are confusing the two issues    How can I make xargs execute the command with exactly one argument for each line of input given  Its default behavior is to chunk the lines around whitespace   then the answer is more subtle  One would think that -L 1 could be of help  but it turns out it doesn t change argument parsing  It only executes the command once for each input line  with as many arguments as were there on that input line    echo   one ntwo nthree and four    xargs -L 1   show  - gt   quot one quot   - gt   quot two quot   - gt   quot three quot   quot and quot   quot four quot    Not only that  but if a line ends with whitespace  it is appended to the next    echo   one  ntwo nthree and four    xargs -L 1   show  - gt   quot one quot   quot two quot   - gt   quot three quot   quot and quot   quot four quot    Clearly  -L is not about changing the way xargs splits the input into arguments  The only argument that does so in a cross-platform fashion  excluding GNU extensions  is -0  which splits the input around NUL bytes  Then  it s just a matter of translating newlines to NUL with the help of tr    echo   one  ntwo nthree and four    tr   n    0    xargs -0   show  - gt   quot one  quot   quot two quot   quot three and four quot    Now the argument parsing looks all right  including the trailing whitespace  Finally  if you combine this technique with -n 1  you get exactly one command execution per input line  whatever input you have  which may be yet another way to look at the original question  possibly the most intuitive  given the title     echo   one  ntwo nthree and four    tr   n    0    xargs -0 -n1   show  - gt   quot one  quot   - gt   quot two quot   - gt   quot three and four quot    As mentioned above  if you are using GNU xargs you can replace the tr with the GNU-specific option -d    echo   one  ntwo nthree and four    xargs -d  n -n1   show  - gt   quot one  quot   - gt   quot two quot   - gt   quot three and four quot

User · Answer

You can limit the number of lines  or arguments  if there are spaces between each argument  using the --max-lines or --max-args flags  respectively     -L max-lines          Use at most max-lines nonblank input lines per command line   Trailing blanks cause an input line to be logically continued on the next  input          line   Implies -x     --max-lines  max-lines   -l max-lines           Synonym  for  the -L option   Unlike -L  the max-lines argument is optional   If max-args is not specified  it defaults to one   The -l option          is deprecated since the POSIX standard specifies -L instead     --max-args max-args  -n max-args          Use at most max-args arguments per command line   Fewer than max-args arguments will be used if the size  see  the  -s  option   is  exceeded           unless the -x option is given  in which case xargs will exit

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The following command will find all the files  -type f  in  path and then copy them using cp to the current folder   Note the use if -I   to specify a placeholder character in the cp command line so that arguments can be placed after the file name   find  path -type f -print0   xargs -0 -I   cp      Tested with xargs  GNU findutils  4 4 0

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If you want to run the command for every line  i e  result  coming from find  then what do you need the xargs for   Try   find path -type f -exec your-command        where the literal    gets substituted by the filename and the literal    is needed for find to know that the custom command ends there   EDIT    after the edit of your question clarifying that you know about -exec   From man xargs      -L max-lines    Use at most max-lines nonblank input lines per command line   Trailing    blanks cause an input line to be logically continued on the next input line     Implies -x    Note that filenames ending in blanks would cause you trouble if you use xargs     mkdir  tmp bax  cd  tmp bax   touch a   b c   c   find   -type f -print   xargs -L1 wc -l 0   c 0   c 0 total 0   b wc    a  No such file or directory   So if you don t care about the -exec option  you better use -print0 and -0     find   -type f -print0   xargs -0L1 wc -l 0   c 0   c 0   b 0   a

User · Answer

In your example  the point of piping the output of find to xargs is that the standard behavior of find s -exec option is to execute the command once for each found file  If you re using find  and you want its standard behavior  then the answer is simple - don t use xargs to begin with

[xargs] Make xargs execute the command once for each line of input

Examples related to xargs