How to iterate over arguments in a Bash script

Question

I have a complex command that I d like to make a shell bash script of   I can write it in terms of  1 easily   foo  1 args -o  1 ext   I want to be able to pass multiple input names to the script  What s the right way to do it     And  of course  I want to handle filenames with spaces in them

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aparse     while        gt  0      do   case   1  in     --arg1        varg1   2        shift              --arg2        varg2 true            esac   shift done    aparse

User · Answer

Amplifying on baz s answer  if you need to enumerate the argument list with an index  such as to search for a specific word   you can do this without copying the list or mutating it   Say you want to split an argument list at a double-dash   --   and pass the arguments before the dashes to one command  and the arguments after the dashes to another    toolwrapper        for i in   seq 1      do             i       --      amp  amp  break    done    return      returns error status if we don t  break      echo  dashes at  i     echo  Before dashes      1 i-1      echo  After dashes      i 1           Results should look like this      toolwrapper args for first tool -- and these are for the second  dashes at 5  Before dashes  args for first tool  After dashes  and these are for the second

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For simple cases you can also use shift  It treats the argument list like a queue  Each shift throws the first argument out and the index of each of the remaining arguments is decremented    this prints all arguments while test    -gt 0 do     echo   1      shift done

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You can also access them as an array elements  for example if you don t want to iterate through all of them  argc    argv         for    j 0  j lt argc  j       do     echo    argv j    done

User · Answer

Use      to represent all the arguments   for var in      do     echo   var  done   This will iterate over each argument and print it out on a separate line      behaves like    except that when quoted the arguments are broken up properly if there are spaces in them   sh test sh 1 2  3 4  1 2 3 4

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For simple cases you can also use shift  It treats the argument list like a queue  Each shift throws the first argument out and the index of each of the remaining arguments is decremented    this prints all arguments while test    -gt 0 do     echo   1      shift done

User · Answer

Amplifying on baz s answer  if you need to enumerate the argument list with an index  such as to search for a specific word   you can do this without copying the list or mutating it   Say you want to split an argument list at a double-dash   --   and pass the arguments before the dashes to one command  and the arguments after the dashes to another    toolwrapper        for i in   seq 1      do             i       --      amp  amp  break    done    return      returns error status if we don t  break      echo  dashes at  i     echo  Before dashes      1 i-1      echo  After dashes      i 1           Results should look like this      toolwrapper args for first tool -- and these are for the second  dashes at 5  Before dashes  args for first tool  After dashes  and these are for the second

User · Answer

getopt Use command in your scripts to format any command line options or parameters      bin bash   Extract command line options  amp  values with getopt   set --   getopt -q ab cd         echo while   -n   1    do case   1  in -a  echo  Found the -a option     -b  param   2  echo  Found the -b option  with parameter value  param  shift    -c  echo  Found the -c option     --  shift break       echo   1 is not an option    esac shift

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Use      to represent all the arguments   for var in      do     echo   var  done   This will iterate over each argument and print it out on a separate line      behaves like    except that when quoted the arguments are broken up properly if there are spaces in them   sh test sh 1 2  3 4  1 2 3 4

User · Answer

aparse     while        gt  0      do   case   1  in     --arg1        varg1   2        shift              --arg2        varg2 true            esac   shift done    aparse

User · Answer

Rewrite of a now-deleted answer by VonC   Robert Gamble s succinct answer deals directly with the question  This one amplifies on some issues with filenames containing spaces   See also    1        in  bin sh  Basic thesis       is correct  and     unquoted  is almost always wrong  This is because      works fine when arguments contain spaces  and works the same as    when they don t  In some circumstances       is OK too  but      usually  but not always  works in the same places  Unquoted     and    are equivalent  and almost always wrong    So  what is the difference between               and        They are all related to  all the arguments to the shell   but they do different things  When unquoted     and    do the same thing   They treat each  word   sequence of non-whitespace  as a separate argument   The quoted forms are quite different  though       treats the argument list as a single space-separated string  whereas      treats the arguments almost exactly as they were when specified on the command line       expands to nothing at all when there are no positional arguments       expands to an empty string  mdash  and yes  there s a difference  though it can be hard to perceive it  See more information below  after the introduction of the  non-standard  command al   Secondary thesis  if you need to process arguments with spaces and then pass them on to other commands  then you sometimes need non-standard tools to assist   Or you should use arrays  carefully     array      behaves analogously to         Example         mkdir  my dir  anotherdir       ls     anotherdir      my dir       cp  dev null  my dir my file        cp  dev null  anotherdir myfile        ls -Fltr     total 0     drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 my dir      drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 anotherdir        ls -Fltr       my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file      anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile       ls -Fltr    my dir     anotherdir        my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file        anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile       var     my dir     anotherdir    amp  amp  echo  var        my dir     anotherdir        ls -Fltr  var     ls     anotherdir   No such file or directory     ls     my  No such file or directory     ls  dir   No such file or directory         Why doesn t that work  It doesn t work because the shell processes quotes before it expands variables  So  to get the shell to pay attention to the quotes embedded in  var  you have to use eval         eval ls -Fltr  var       my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file        anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile          This gets really tricky when you have file names such as  He said   Don t do this     with quotes and double quotes and spaces          cp  dev null  He said    Don t do this           ls     He said   Don t do this         anotherdir                      my dir       ls -l     total 0     -rw-r--r--   1 jleffler  staff    0 Nov  1 15 54 He said   Don t do this       drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 anotherdir     drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 my dir          The shells  all of them  do not make it particularly easy to handle such stuff  so  funnily enough  many Unix programs do not do a good job of handling them  On Unix  a filename  single component  can contain any characters except slash and NUL   0   However  the shells strongly encourage no spaces or newlines or tabs anywhere in a path names  It is also why standard Unix file names do not contain spaces  etc   When dealing with file names that may contain spaces and other troublesome characters  you have to be extremely careful  and I found long ago that I needed a program that is not standard on Unix  I call it escape  version 1 1 was dated 1989-08-23T16 01 45Z    Here is an example of escape in use - with the SCCS control system  It is a cover script that does both a delta  think check-in  and a get  think check-out   Various arguments  especially -y  the reason why you made the change  would contain blanks and newlines  Note that the script dates from 1992  so it uses back-ticks instead of   cmd      notation and does not use    bin sh on the first line             Id  delget sh v 1 8 1992 12 29 10 46 21 jl Exp          Delta and get files     Uses escape to allow for all weird combinations of quotes in arguments  case  basename  0  sh  in deledit     eflag  -e    esac  sflag  -s  for arg in      do     case   arg  in     -r      gargs   gargs  escape    arg                 dargs   dargs  escape    arg                        -e      gargs   gargs  escape    arg                 sflag                eflag                       -       dargs   dargs  escape    arg                                gargs   gargs  escape    arg                 dargs   dargs  escape    arg                        esac done  eval delta   dargs   amp  amp  eval get  eflag  sflag   gargs     I would probably not use escape quite so thoroughly these days - it is not needed with the -e argument  for example - but overall  this is one of my simpler scripts using escape    The escape program simply outputs its arguments  rather like echo does  but it ensures that the arguments are protected for use with eval  one level of eval  I do have a program which did remote shell execution  and that needed to escape the output of escape          escape  var         my   dir       anotherdir         escape   var          my dir     anotherdir         escape x y z     x y z          I have another program called al that lists its arguments one per line  and it is even more ancient  version 1 1 dated 1987-01-27T14 35 49   It is most useful when debugging scripts  as it can be plugged into a command line to see what arguments are actually passed to the command         echo   var         my dir     anotherdir        al  var        my     dir         anotherdir        al   var         my dir     anotherdir           Added  And now to show the difference between the various      notations  here is one more example     cat xx sh set -x al    al    al      al        sh xx sh                  al He said    Don    t  do  this    anotherdir my dir xx sh anotherdir myfile my dir my file He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al He said    Don    t  do  this    anotherdir my dir xx sh anotherdir myfile my dir my file He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al  He said   Don    t do this   anotherdir my dir xx sh anotherdir myfile my dir my file  He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al  He said   Don    t do this    anotherdir  my dir  xx sh anotherdir myfile  my dir my file  He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file     Notice that nothing preserves the original blanks between the   and     on the command line   Also  note that you can change the  command line arguments  in the shell by using   set -- -new -opt and  arg with space    This sets 4 options   -new    -opt    and   and  arg with space       Hmm  that s quite a long answer - perhaps exegesis is the better term  Source code for escape available on request  email to firstname dot lastname at gmail dot com   The source code for al is incredibly simple    include  lt stdio h gt  int main int argc  char   argv        while     argv    0          puts  argv       return 0       That s all   It is equivalent to the test sh script that Robert Gamble showed  and could be written as a shell function  but shell functions didn t exist in the local version of Bourne shell when I first wrote al    Also note that you can write al as a simple shell script           0    amp  amp  printf   s n         The conditional is needed so that it produces no output when passed no arguments   The printf command will produce a blank line with only the format string argument  but the C program produces nothing

User · Answer

getopt Use command in your scripts to format any command line options or parameters      bin bash   Extract command line options  amp  values with getopt   set --   getopt -q ab cd         echo while   -n   1    do case   1  in -a  echo  Found the -a option     -b  param   2  echo  Found the -b option  with parameter value  param  shift    -c  echo  Found the -c option     --  shift break       echo   1 is not an option    esac shift

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Rewrite of a now-deleted answer by VonC   Robert Gamble s succinct answer deals directly with the question  This one amplifies on some issues with filenames containing spaces   See also    1        in  bin sh  Basic thesis       is correct  and     unquoted  is almost always wrong  This is because      works fine when arguments contain spaces  and works the same as    when they don t  In some circumstances       is OK too  but      usually  but not always  works in the same places  Unquoted     and    are equivalent  and almost always wrong    So  what is the difference between               and        They are all related to  all the arguments to the shell   but they do different things  When unquoted     and    do the same thing   They treat each  word   sequence of non-whitespace  as a separate argument   The quoted forms are quite different  though       treats the argument list as a single space-separated string  whereas      treats the arguments almost exactly as they were when specified on the command line       expands to nothing at all when there are no positional arguments       expands to an empty string  mdash  and yes  there s a difference  though it can be hard to perceive it  See more information below  after the introduction of the  non-standard  command al   Secondary thesis  if you need to process arguments with spaces and then pass them on to other commands  then you sometimes need non-standard tools to assist   Or you should use arrays  carefully     array      behaves analogously to         Example         mkdir  my dir  anotherdir       ls     anotherdir      my dir       cp  dev null  my dir my file        cp  dev null  anotherdir myfile        ls -Fltr     total 0     drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 my dir      drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 anotherdir        ls -Fltr       my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file      anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile       ls -Fltr    my dir     anotherdir        my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file        anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile       var     my dir     anotherdir    amp  amp  echo  var        my dir     anotherdir        ls -Fltr  var     ls     anotherdir   No such file or directory     ls     my  No such file or directory     ls  dir   No such file or directory         Why doesn t that work  It doesn t work because the shell processes quotes before it expands variables  So  to get the shell to pay attention to the quotes embedded in  var  you have to use eval         eval ls -Fltr  var       my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file        anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile          This gets really tricky when you have file names such as  He said   Don t do this     with quotes and double quotes and spaces          cp  dev null  He said    Don t do this           ls     He said   Don t do this         anotherdir                      my dir       ls -l     total 0     -rw-r--r--   1 jleffler  staff    0 Nov  1 15 54 He said   Don t do this       drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 anotherdir     drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 my dir          The shells  all of them  do not make it particularly easy to handle such stuff  so  funnily enough  many Unix programs do not do a good job of handling them  On Unix  a filename  single component  can contain any characters except slash and NUL   0   However  the shells strongly encourage no spaces or newlines or tabs anywhere in a path names  It is also why standard Unix file names do not contain spaces  etc   When dealing with file names that may contain spaces and other troublesome characters  you have to be extremely careful  and I found long ago that I needed a program that is not standard on Unix  I call it escape  version 1 1 was dated 1989-08-23T16 01 45Z    Here is an example of escape in use - with the SCCS control system  It is a cover script that does both a delta  think check-in  and a get  think check-out   Various arguments  especially -y  the reason why you made the change  would contain blanks and newlines  Note that the script dates from 1992  so it uses back-ticks instead of   cmd      notation and does not use    bin sh on the first line             Id  delget sh v 1 8 1992 12 29 10 46 21 jl Exp          Delta and get files     Uses escape to allow for all weird combinations of quotes in arguments  case  basename  0  sh  in deledit     eflag  -e    esac  sflag  -s  for arg in      do     case   arg  in     -r      gargs   gargs  escape    arg                 dargs   dargs  escape    arg                        -e      gargs   gargs  escape    arg                 sflag                eflag                       -       dargs   dargs  escape    arg                                gargs   gargs  escape    arg                 dargs   dargs  escape    arg                        esac done  eval delta   dargs   amp  amp  eval get  eflag  sflag   gargs     I would probably not use escape quite so thoroughly these days - it is not needed with the -e argument  for example - but overall  this is one of my simpler scripts using escape    The escape program simply outputs its arguments  rather like echo does  but it ensures that the arguments are protected for use with eval  one level of eval  I do have a program which did remote shell execution  and that needed to escape the output of escape          escape  var         my   dir       anotherdir         escape   var          my dir     anotherdir         escape x y z     x y z          I have another program called al that lists its arguments one per line  and it is even more ancient  version 1 1 dated 1987-01-27T14 35 49   It is most useful when debugging scripts  as it can be plugged into a command line to see what arguments are actually passed to the command         echo   var         my dir     anotherdir        al  var        my     dir         anotherdir        al   var         my dir     anotherdir           Added  And now to show the difference between the various      notations  here is one more example     cat xx sh set -x al    al    al      al        sh xx sh                  al He said    Don    t  do  this    anotherdir my dir xx sh anotherdir myfile my dir my file He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al He said    Don    t  do  this    anotherdir my dir xx sh anotherdir myfile my dir my file He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al  He said   Don    t do this   anotherdir my dir xx sh anotherdir myfile my dir my file  He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al  He said   Don    t do this    anotherdir  my dir  xx sh anotherdir myfile  my dir my file  He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file     Notice that nothing preserves the original blanks between the   and     on the command line   Also  note that you can change the  command line arguments  in the shell by using   set -- -new -opt and  arg with space    This sets 4 options   -new    -opt    and   and  arg with space       Hmm  that s quite a long answer - perhaps exegesis is the better term  Source code for escape available on request  email to firstname dot lastname at gmail dot com   The source code for al is incredibly simple    include  lt stdio h gt  int main int argc  char   argv        while     argv    0          puts  argv       return 0       That s all   It is equivalent to the test sh script that Robert Gamble showed  and could be written as a shell function  but shell functions didn t exist in the local version of Bourne shell when I first wrote al    Also note that you can write al as a simple shell script           0    amp  amp  printf   s n         The conditional is needed so that it produces no output when passed no arguments   The printf command will produce a blank line with only the format string argument  but the C program produces nothing

User · Answer

Use      to represent all the arguments   for var in      do     echo   var  done   This will iterate over each argument and print it out on a separate line      behaves like    except that when quoted the arguments are broken up properly if there are spaces in them   sh test sh 1 2  3 4  1 2 3 4

User · Answer

Loop against     the number of arguments variable  works too      bin bash  for   i 1  i lt      i     do   printf  quot    i  n quot  done  test sh 1 2  3 4   Ouput  1 2 3 4

User · Answer

Rewrite of a now-deleted answer by VonC   Robert Gamble s succinct answer deals directly with the question  This one amplifies on some issues with filenames containing spaces   See also    1        in  bin sh  Basic thesis       is correct  and     unquoted  is almost always wrong  This is because      works fine when arguments contain spaces  and works the same as    when they don t  In some circumstances       is OK too  but      usually  but not always  works in the same places  Unquoted     and    are equivalent  and almost always wrong    So  what is the difference between               and        They are all related to  all the arguments to the shell   but they do different things  When unquoted     and    do the same thing   They treat each  word   sequence of non-whitespace  as a separate argument   The quoted forms are quite different  though       treats the argument list as a single space-separated string  whereas      treats the arguments almost exactly as they were when specified on the command line       expands to nothing at all when there are no positional arguments       expands to an empty string  mdash  and yes  there s a difference  though it can be hard to perceive it  See more information below  after the introduction of the  non-standard  command al   Secondary thesis  if you need to process arguments with spaces and then pass them on to other commands  then you sometimes need non-standard tools to assist   Or you should use arrays  carefully     array      behaves analogously to         Example         mkdir  my dir  anotherdir       ls     anotherdir      my dir       cp  dev null  my dir my file        cp  dev null  anotherdir myfile        ls -Fltr     total 0     drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 my dir      drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 anotherdir        ls -Fltr       my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file      anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile       ls -Fltr    my dir     anotherdir        my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file        anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile       var     my dir     anotherdir    amp  amp  echo  var        my dir     anotherdir        ls -Fltr  var     ls     anotherdir   No such file or directory     ls     my  No such file or directory     ls  dir   No such file or directory         Why doesn t that work  It doesn t work because the shell processes quotes before it expands variables  So  to get the shell to pay attention to the quotes embedded in  var  you have to use eval         eval ls -Fltr  var       my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file        anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile          This gets really tricky when you have file names such as  He said   Don t do this     with quotes and double quotes and spaces          cp  dev null  He said    Don t do this           ls     He said   Don t do this         anotherdir                      my dir       ls -l     total 0     -rw-r--r--   1 jleffler  staff    0 Nov  1 15 54 He said   Don t do this       drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 anotherdir     drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 my dir          The shells  all of them  do not make it particularly easy to handle such stuff  so  funnily enough  many Unix programs do not do a good job of handling them  On Unix  a filename  single component  can contain any characters except slash and NUL   0   However  the shells strongly encourage no spaces or newlines or tabs anywhere in a path names  It is also why standard Unix file names do not contain spaces  etc   When dealing with file names that may contain spaces and other troublesome characters  you have to be extremely careful  and I found long ago that I needed a program that is not standard on Unix  I call it escape  version 1 1 was dated 1989-08-23T16 01 45Z    Here is an example of escape in use - with the SCCS control system  It is a cover script that does both a delta  think check-in  and a get  think check-out   Various arguments  especially -y  the reason why you made the change  would contain blanks and newlines  Note that the script dates from 1992  so it uses back-ticks instead of   cmd      notation and does not use    bin sh on the first line             Id  delget sh v 1 8 1992 12 29 10 46 21 jl Exp          Delta and get files     Uses escape to allow for all weird combinations of quotes in arguments  case  basename  0  sh  in deledit     eflag  -e    esac  sflag  -s  for arg in      do     case   arg  in     -r      gargs   gargs  escape    arg                 dargs   dargs  escape    arg                        -e      gargs   gargs  escape    arg                 sflag                eflag                       -       dargs   dargs  escape    arg                                gargs   gargs  escape    arg                 dargs   dargs  escape    arg                        esac done  eval delta   dargs   amp  amp  eval get  eflag  sflag   gargs     I would probably not use escape quite so thoroughly these days - it is not needed with the -e argument  for example - but overall  this is one of my simpler scripts using escape    The escape program simply outputs its arguments  rather like echo does  but it ensures that the arguments are protected for use with eval  one level of eval  I do have a program which did remote shell execution  and that needed to escape the output of escape          escape  var         my   dir       anotherdir         escape   var          my dir     anotherdir         escape x y z     x y z          I have another program called al that lists its arguments one per line  and it is even more ancient  version 1 1 dated 1987-01-27T14 35 49   It is most useful when debugging scripts  as it can be plugged into a command line to see what arguments are actually passed to the command         echo   var         my dir     anotherdir        al  var        my     dir         anotherdir        al   var         my dir     anotherdir           Added  And now to show the difference between the various      notations  here is one more example     cat xx sh set -x al    al    al      al        sh xx sh                  al He said    Don    t  do  this    anotherdir my dir xx sh anotherdir myfile my dir my file He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al He said    Don    t  do  this    anotherdir my dir xx sh anotherdir myfile my dir my file He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al  He said   Don    t do this   anotherdir my dir xx sh anotherdir myfile my dir my file  He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al  He said   Don    t do this    anotherdir  my dir  xx sh anotherdir myfile  my dir my file  He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file     Notice that nothing preserves the original blanks between the   and     on the command line   Also  note that you can change the  command line arguments  in the shell by using   set -- -new -opt and  arg with space    This sets 4 options   -new    -opt    and   and  arg with space       Hmm  that s quite a long answer - perhaps exegesis is the better term  Source code for escape available on request  email to firstname dot lastname at gmail dot com   The source code for al is incredibly simple    include  lt stdio h gt  int main int argc  char   argv        while     argv    0          puts  argv       return 0       That s all   It is equivalent to the test sh script that Robert Gamble showed  and could be written as a shell function  but shell functions didn t exist in the local version of Bourne shell when I first wrote al    Also note that you can write al as a simple shell script           0    amp  amp  printf   s n         The conditional is needed so that it produces no output when passed no arguments   The printf command will produce a blank line with only the format string argument  but the C program produces nothing

User · Answer

Use      to represent all the arguments   for var in      do     echo   var  done   This will iterate over each argument and print it out on a separate line      behaves like    except that when quoted the arguments are broken up properly if there are spaces in them   sh test sh 1 2  3 4  1 2 3 4

User · Answer

Loop against     the number of arguments variable  works too      bin bash  for   i 1  i lt      i     do   printf  quot    i  n quot  done  test sh 1 2  3 4   Ouput  1 2 3 4

User · Answer

Note that Robert s answer is correct  and it works in sh as well   You can  portably  simplify it even further   for i in        is equivalent to   for i   I e   you don t need anything   Testing    is command prompt      set a b  spaces here  d   for i  do echo   i   done a b spaces here d   for i in       do echo   i   done a b spaces here d   I first read about this in Unix Programming Environment by Kernighan and Pike   In bash  help for documents this      for NAME  in WORDS        do COMMANDS  done      If  in WORDS       is not present  then  in       is assumed

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Rewrite of a now-deleted answer by VonC   Robert Gamble s succinct answer deals directly with the question  This one amplifies on some issues with filenames containing spaces   See also    1        in  bin sh  Basic thesis       is correct  and     unquoted  is almost always wrong  This is because      works fine when arguments contain spaces  and works the same as    when they don t  In some circumstances       is OK too  but      usually  but not always  works in the same places  Unquoted     and    are equivalent  and almost always wrong    So  what is the difference between               and        They are all related to  all the arguments to the shell   but they do different things  When unquoted     and    do the same thing   They treat each  word   sequence of non-whitespace  as a separate argument   The quoted forms are quite different  though       treats the argument list as a single space-separated string  whereas      treats the arguments almost exactly as they were when specified on the command line       expands to nothing at all when there are no positional arguments       expands to an empty string  mdash  and yes  there s a difference  though it can be hard to perceive it  See more information below  after the introduction of the  non-standard  command al   Secondary thesis  if you need to process arguments with spaces and then pass them on to other commands  then you sometimes need non-standard tools to assist   Or you should use arrays  carefully     array      behaves analogously to         Example         mkdir  my dir  anotherdir       ls     anotherdir      my dir       cp  dev null  my dir my file        cp  dev null  anotherdir myfile        ls -Fltr     total 0     drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 my dir      drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 anotherdir        ls -Fltr       my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file      anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile       ls -Fltr    my dir     anotherdir        my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file        anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile       var     my dir     anotherdir    amp  amp  echo  var        my dir     anotherdir        ls -Fltr  var     ls     anotherdir   No such file or directory     ls     my  No such file or directory     ls  dir   No such file or directory         Why doesn t that work  It doesn t work because the shell processes quotes before it expands variables  So  to get the shell to pay attention to the quotes embedded in  var  you have to use eval         eval ls -Fltr  var       my dir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 my file        anotherdir      total 0     -rw-r--r--   1 jleffler  staff  0 Nov  1 14 55 myfile          This gets really tricky when you have file names such as  He said   Don t do this     with quotes and double quotes and spaces          cp  dev null  He said    Don t do this           ls     He said   Don t do this         anotherdir                      my dir       ls -l     total 0     -rw-r--r--   1 jleffler  staff    0 Nov  1 15 54 He said   Don t do this       drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 anotherdir     drwxr-xr-x   3 jleffler  staff  102 Nov  1 14 55 my dir          The shells  all of them  do not make it particularly easy to handle such stuff  so  funnily enough  many Unix programs do not do a good job of handling them  On Unix  a filename  single component  can contain any characters except slash and NUL   0   However  the shells strongly encourage no spaces or newlines or tabs anywhere in a path names  It is also why standard Unix file names do not contain spaces  etc   When dealing with file names that may contain spaces and other troublesome characters  you have to be extremely careful  and I found long ago that I needed a program that is not standard on Unix  I call it escape  version 1 1 was dated 1989-08-23T16 01 45Z    Here is an example of escape in use - with the SCCS control system  It is a cover script that does both a delta  think check-in  and a get  think check-out   Various arguments  especially -y  the reason why you made the change  would contain blanks and newlines  Note that the script dates from 1992  so it uses back-ticks instead of   cmd      notation and does not use    bin sh on the first line             Id  delget sh v 1 8 1992 12 29 10 46 21 jl Exp          Delta and get files     Uses escape to allow for all weird combinations of quotes in arguments  case  basename  0  sh  in deledit     eflag  -e    esac  sflag  -s  for arg in      do     case   arg  in     -r      gargs   gargs  escape    arg                 dargs   dargs  escape    arg                        -e      gargs   gargs  escape    arg                 sflag                eflag                       -       dargs   dargs  escape    arg                                gargs   gargs  escape    arg                 dargs   dargs  escape    arg                        esac done  eval delta   dargs   amp  amp  eval get  eflag  sflag   gargs     I would probably not use escape quite so thoroughly these days - it is not needed with the -e argument  for example - but overall  this is one of my simpler scripts using escape    The escape program simply outputs its arguments  rather like echo does  but it ensures that the arguments are protected for use with eval  one level of eval  I do have a program which did remote shell execution  and that needed to escape the output of escape          escape  var         my   dir       anotherdir         escape   var          my dir     anotherdir         escape x y z     x y z          I have another program called al that lists its arguments one per line  and it is even more ancient  version 1 1 dated 1987-01-27T14 35 49   It is most useful when debugging scripts  as it can be plugged into a command line to see what arguments are actually passed to the command         echo   var         my dir     anotherdir        al  var        my     dir         anotherdir        al   var         my dir     anotherdir           Added  And now to show the difference between the various      notations  here is one more example     cat xx sh set -x al    al    al      al        sh xx sh                  al He said    Don    t  do  this    anotherdir my dir xx sh anotherdir myfile my dir my file He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al He said    Don    t  do  this    anotherdir my dir xx sh anotherdir myfile my dir my file He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al  He said   Don    t do this   anotherdir my dir xx sh anotherdir myfile my dir my file  He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file   al  He said   Don    t do this    anotherdir  my dir  xx sh anotherdir myfile  my dir my file  He said   Don t do this   anotherdir my dir xx sh anotherdir myfile my dir my file     Notice that nothing preserves the original blanks between the   and     on the command line   Also  note that you can change the  command line arguments  in the shell by using   set -- -new -opt and  arg with space    This sets 4 options   -new    -opt    and   and  arg with space       Hmm  that s quite a long answer - perhaps exegesis is the better term  Source code for escape available on request  email to firstname dot lastname at gmail dot com   The source code for al is incredibly simple    include  lt stdio h gt  int main int argc  char   argv        while     argv    0          puts  argv       return 0       That s all   It is equivalent to the test sh script that Robert Gamble showed  and could be written as a shell function  but shell functions didn t exist in the local version of Bourne shell when I first wrote al    Also note that you can write al as a simple shell script           0    amp  amp  printf   s n         The conditional is needed so that it produces no output when passed no arguments   The printf command will produce a blank line with only the format string argument  but the C program produces nothing

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Note that Robert s answer is correct  and it works in sh as well   You can  portably  simplify it even further   for i in        is equivalent to   for i   I e   you don t need anything   Testing    is command prompt      set a b  spaces here  d   for i  do echo   i   done a b spaces here d   for i in       do echo   i   done a b spaces here d   I first read about this in Unix Programming Environment by Kernighan and Pike   In bash  help for documents this      for NAME  in WORDS        do COMMANDS  done      If  in WORDS       is not present  then  in       is assumed

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You can also access them as an array elements  for example if you don t want to iterate through all of them  argc    argv         for    j 0  j lt argc  j       do     echo    argv j    done

[bash] How to iterate over arguments in a Bash script

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