Executing multi-line statements in the one-line command-line

Question

I m using Python with -c to execute a one-liner loop  i e      python -c  for r in range 10   print  rob     This works fine  However  if I import a module before the for loop  I get a syntax error     python -c  import sys  for r in range 10   print  rob     File   lt string gt    line 1     import sys  for r in range 10   print  rob                  SyntaxError  invalid syntax   Any idea how this can be fixed   It s important to me to have this as a one-liner so that I can include it in a Makefile

User · Answer

just use return and type it on the next line   user host    python -c  import sys  gt  for r in range 10   print  rob   rob rob

User · Answer

Any idea how this can be fixed    Your problem is created by the fact that Python statements  separated by    are only allowed to be  small statements   which are all one-liners  From the grammar file in the Python docs    stmt  simple stmt   compound stmt simple stmt  small stmt      small stmt         NEWLINE small stmt   expr stmt   del stmt   pass stmt   flow stmt                import stmt   global stmt   nonlocal stmt   assert stmt     Compound statements can t be included on the same line with other statements via semicolons - so doing this with the -c flag becomes very inconvenient    When demonstrating Python while in a bash shell environment  I find it very useful to include compound statements  The only simple way of doing this reliably is with heredocs  a posix shell thing    Heredocs  Use a heredoc  created with  lt  lt   and Python s command line interface option  -     python -  lt  lt - EOF          import sys                      1 tab indent         for r in range 10               1 tab indent             print  rob                  1 tab indent and 4 spaces EOF   Adding the - after  lt  lt   the  lt  lt -  allows you to use tabs to indent  Stackoverflow converts tabs to spaces  so I ve indented 8 spaces to emphasize this   The leading tabs will be stripped   You can do it without the tabs with just  lt  lt      python -  lt  lt   EOF  import sys for r in range 10       print  rob   EOF   Putting quotes around EOF prevents parameter and arithmetic expansion  This makes the heredoc more robust   Bash multiline strings  If you use double-quotes  you ll get shell-expansion     python -c    gt  import sys  gt  for p in   PATH  split        gt      print p   gt     usr sbin  usr bin  sbin  bin       To avoid shell expansion use single-quotes     python -c    gt  import sys  gt  for p in   PATH  split        gt      print p   gt     PATH   Note that we need to swap the quote characters on the literals in Python - we basically can t use quote character being interpreted by BASH  We can alternate them though  like we can in Python - but this already looks quite confusing  which is why I don t recommend this     python -c   import sys for p in     PATH    split           print p     usr sbin  usr bin  sbin  bin       Critique of the accepted answer  and others   This is not very readable    echo -e  import sys nfor r in range 10   print  rob     python    Not very readable  and additionally difficult to debug in the case of an error    python -c  exec   import sys  nfor r in range 10   print  rob         Perhaps a bit more readable  but still quite ugly     echo  import sys    echo  for r in range 10   print  rob      python    You ll have a bad time if you have   s in your python      python -c  import sys  gt  for r in range 10   print  rob      Don t abuse map or list comprehensions to get for-loops    python -c  import sys  map lambda x  sys stdout write  rob d n    x   range 10       These are all sad and bad  Don t do them

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answered Nov 23  10 at 19 48  I m not really a big Pythoner - but I found this syntax once  forgot where from  so I thought I d document it    if you use sys stdout write instead of print  the difference being  sys stdout write takes arguments as a function  in parenthesis - whereas print doesn t   then for a one-liner  you can get away with inverting the order of the command and the for  removing the semicolon  and enclosing the command in square brackets  i e     python -c  import sys   sys stdout write  rob n   for r in range 10      Have no idea how this syntax would be called in Python      Hope this helps    Cheers       EDIT Tue Apr 9 20 57 30 2013  Well  I think I finally found what these square brackets in one-liners are about  they are  list comprehensions   apparently   first note this in Python 2 7     STR abc   echo  STR   python -c  import sys re  a  sys stdout write line  for line in sys stdin   print a   lt generator object  lt genexpr gt  at 0xb771461c gt    So the command in round brackets parenthesis is seen as a  generator object   if we  iterate  through it by calling next   - then the command inside the parenthesis will be executed  note the  abc  in the output      echo  STR   python -c  import sys re  a  sys stdout write line  for line in sys stdin   a next     print a  abc  lt generator object  lt genexpr gt  at 0xb777b734 gt    If we now use square brackets - note that we don t need to call next   to have the command execute  it executes immediately upon assignment  however  later inspection reveals that a is None     echo  STR   python -c  import sys re  a  sys stdout write line  for line in sys stdin   print a  abc  None    This doesn t leave much info to look for  for the square brackets case - but I stumbled upon this page which I think explains    Python Tips And Tricks     First Edition - Python Tutorials   Dream In Code      If you recall  the standard format of a single line generator is a kind of one line  for  loop inside brackets  This will produce a  one-shot  iterable object which is an object you can iterate over in only one direction and which you can t re-use once you reach the end       A  list comprehension  looks almost the same as a regular one-line generator  except that the regular brackets -     - are replaced by square brackets -      The major advanatge of alist comprehension is that produces a  list   rather than a  one-shot  iterable object  so that you can go back and forth through it  add elements  sort  etc    And indeed it is a list - it s just its first element becomes none as soon as it is executed     echo  STR   python -c  import sys re  print  sys stdout write line  for line in sys stdin    class    abc  lt type  list  gt    echo  STR   python -c  import sys re  print  sys stdout write line  for line in sys stdin  0   abc None   List comprehensions are otherwise documented in 5  Data Structures  5 1 4  List Comprehensions     Python v2 7 4 documentation as  List comprehensions provide a concise way to create lists   presumably  that s where the limited  executability  of lists comes into play in one-liners   Well  hope I m not terribly too off the mark here      EDIT2  and here is a one-liner command line with two non-nested for-loops  both enclosed within  list comprehension  square brackets     echo  STR   python -c  import sys re  a  sys stdout write line  for line in sys stdin   b  sys stdout write str x   for x in range 2     print a   print b  abc 01 None   None  None    Notice that the second  list  b now has two elements  since its for loop explicitly ran twice  however  the result of sys stdout write   in both cases was  apparently  None

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- To make this answer work with Python 3 x as well  print is called as a function  in 3 x  only print  foo   works  whereas 2 x also accepts print  foo   - For a cross-platform perspective that includes Windows  see kxr s helpful answer   In bash  ksh  or zsh   Use an ANSI C-quoted string           which allows using  n to represent newlines that are expanded to actual newlines before the string is passed to python   python -c   import sys nfor r in range 10   print  rob      Note the  n between the import and for statements to effect a line break   To pass shell-variable values to such a command  it is safest to use arguments and access them via sys argv inside the Python script     name  rob    value to pass to the Python script python -c   import sys nfor r in range 10   print sys argv 1      name    See below for a discussion of the pros and cons of using an  escape sequence-preprocessed  double-quoted command string with embedded shell-variable references   To work safely with        strings    Double   instances in your original source code      lt char gt  sequences - such as  n in this case  but also the usual suspects such as  t   r   b - are expanded by         see man printf for the supported escapes   Escape   instances as         If you must remain POSIX-compliant   Use printf with a command substitution   python -c    printf  b  import sys nfor r in range 10   print  rob        To work safely with this type of string    Double   instances in your original source code      lt char gt  sequences - such as  n in this case  but also the usual suspects such as  t   r   b - are expanded by printf  see man printf for the supported escape sequences    Pass a single-quoted string to printf  b and escape embedded single quotes as       sic     Using single quotes protects the string s contents from interpretation by the shell    That said  for short Python scripts  as in this case  you can use a double-quoted string to incorporate shell variable values into your scripts - as long as you re aware of the associated pitfalls  see next point   e g   the shell expands  HOME to the current user s home dir  in the following command    python -c    printf  b  import sys nfor r in range 10   print  rob is  HOME       However  the generally preferred approach is to pass values from the shell via arguments  and access them via sys argv in Python  the equivalent of the above command is    python -c    printf  b  import sys nfor r in range 10   print  rob is     sys argv 1        HOME    While using a double-quoted string is more convenient - it allows you to use embedded single quotes unescaped and embedded double quotes as    - it also makes the string subject to interpretation by the shell  which may or may not be the intent    and   characters in your source code that are not meant for the shell may cause a syntax error or alter the string unexpectedly    Additionally  the shell s own   processing in double-quoted strings can get in the way  for instance  to get Python to produce literal output ro b  you must pass ro  b to it  with a       shell string and doubled   instances  we get  python -c    printf  b  import sys nprint  ro    bs        ok   ro bs  By contrast  this does not work as intended with a       shell string  python -c    printf  b  import sys nprint  ro    bs           INCORRECT   rs  The shell interprets both   b  and    b  as literal  b  requiring a dizzying number of additional   instances to achieve the desired effect  python -c    printf  b  import sys nprint  ro        bs            To pass the code via stdin rather than -c   Note  I m focusing on single-line solutions here  xorho s answer shows how to use a multi-line here-document - be sure to quote the delimiter  however  e g    lt  lt  EOF   unless you explicitly want the shell to expand the string up front  which comes with the caveats noted above      In bash  ksh  or zsh   Combine an ANSI C-quoted string          with a here-string   lt  lt  lt        python -  lt  lt  lt   import sys nfor r in range 10   print  rob      - tells python explicitly to read from stdin  which it does by default   - is optional in this case  but if you also want to pass arguments to the scripts  you do need it to disambiguate the argument from a script filename   python -  rob   lt  lt  lt   import sys nfor r in range 10   print sys argv 1        If you must remain POSIX-compliant   Use printf as above  but with a pipeline so as to pass its output via stdin   printf  b  import sys nfor r in range 10   print  rob      python   With an argument   printf  b  import sys nfor r in range 10   print sys argv 1      python -  rob

User · Answer

This script provides a Perl-like command line interface   Pyliner - Script to run arbitrary Python code on the command line  Python recipe

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I wanted a solution with the following properties    Readable Read stdin for processing output of other tools   Both requirements were not provided in the other answers  so here s how to read stdin while doing everything on the command line   grep special string -r   sort   python3  lt  cat  lt  lt EOF import sys for line in sys stdin      tokens   line split       if len tokens     4          print   -45s  7 3f     s     s     tokens 0   float tokens 1    tokens 2   tokens 3    EOF

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If your system is Posix 2 compliant it should supply the printf utility     printf  print  zap  nfor r in range 3   print  rob     python zap rob rob rob

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This variant is most portable for putting multi-line scripts on command-line on Windows and  nix  py2 3  without pipes   python -c  exec   import sys  nfor r in range 10   print  rob           None of the other examples seen here so far did so    Neat on Windows is   python -c exec   import sys  nfor r in range 10   print  rob      python -c exec    import sys  nfor r in range 10   print  rob          Neat on bash  nix is   python -c   import sys  nfor r in range 10   print  rob        This function turns any multiline-script into a portable command-one-liner   def py2cmdline script       exs    exec  r     re sub   r n  r     n   script rstrip        print  python -c   s     exs replace      r         Usage    gt  gt  gt  py2cmdline getcliptext    python -c  exec  print   AA tA   ntry  n for i in 1  2  3  n  print i   0 nexcept  n print       longer nmessage            Input was   print  AA   A  try   for i in 1  2  3    print i   0 except   print    longer message

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this style can be used in makefiles too  and in fact it is used quite often    python -  lt  lt EOF import sys for r in range 3   print  rob  EOF   or  python -  lt  lt -EOF     import sys     for r in range 3   print  rob  EOF   in latter case leading tab characters are removed too  and some structured outlook can be achieved   instead of EOF can stand any marker word not appearing in the here document at a beginning of a line  see also here documents in the bash manpage or here

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The issue is not actually with the import statement  it s with anything being before the for loop  Or more specifically  anything appearing before an inlined block   For example  these all work   python -c  import sys  print  rob   python -c  import sys  sys stdout write  rob n      If import being a statement were an issue  this would work  but it doesn t   python -c    import    sys    for r in range 10   print  rob     For your very basic example  you could rewrite it as this   python -c  import sys  map lambda x  sys stdout write  rob d n    x   range 10      However  lambdas can only execute expressions  not statements or multiple statements  so you may still be unable to do the thing you want to do   However  between generator expressions  list comprehension  lambdas  sys stdout write  the  map  builtin  and some creative string interpolation  you can do some powerful one-liners   The question is  how far do you want to go  and at what point is it not better to write a small  py file which your makefile executes instead

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If you don t want to touch stdin and simulate as if you had passed  python cmdfile py   you can do the following from a bash shell     python   lt  printf  word raw input  Enter word     nimport sys nfor i in range 5   n    print word      As you can see  it allows you to use stdin for reading input data  Internally the shell creates the temporary file for the input command contents

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you could do  echo -e  import sys nfor r in range 10   print  rob     python   or w out pipes   python -c  exec   import sys nfor r in range 10   print  rob         or   echo  import sys    echo  for r in range 10   print  rob      python   or  SilentGhost s answer    Crast s answer

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use python -c with triple-quotes python -c  quot  quot  quot  import os os system  pwd   os system  ls -l   print  Hello World    for   in range 5       print     quot  quot  quot

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python2 6 -c  import sys   sys stdout write  rob n   for r in range 10     Works fine  Use       to inline your for loop

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When I needed to do this  I use  python -c    echo -e  import sys nsys stdout write  Hello World    n        Note the triple backslash for the newline in the sys stdout write statement

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The problem is not with the import statement   The problem is that the control flow statements don t work inlined in a python command  Replace that import statement with any other statement and you ll see the same problem   Think about it  python can t possibly inline everything   It uses indentation to group control-flow

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single double quotes and backslash everywhere     python -c  exec  import sys nfor i in range 10   print   bob        Much better     python -c    gt  import sys  gt  for i in range 10    gt    print  bob   gt

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there is one more option  sys stdout write returns None  which keep the list empty    cat somefile log python -c  import sys  line for line in sys stdin if sys stdout write line 2

[python] Executing multi-line statements in the one-line command-line?

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