Executing Python multi-line statements in the one-

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 "<string>", 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.

Answer 1

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

Answer 2

single/double quotes and backslash everywhere:

$ python -c 'exec("import sys\nfor i in range(10): print \"bob\"")'

Much better:

$ python -c '
> import sys
> for i in range(10):
>   print "bob"
> '

Answer 3

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.

Answer 4

This script provides a Perl-like command line interface:

Pyliner - Script to run arbitrary Python code on the command line (Python recipe)

Answer 5

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  <(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.

Answer 6

<sup>- 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.</sup>

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.
  • \<char> 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.
  • \<char> 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., <<'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 (<<<...):

python - <<<$'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' <<<$'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'