Multiline shebang: Difference between revisions
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=={{header|Phix}}==
<!--(notonline)-->
Obviously this is not pwa/p2js compatible, since you cannot run bash or sed (with redirection) or phix or 'rm tmp.eu' from within a browser, and is only intended to be run on Linux, though you could perhaps run it on Windows but only in some kind of bash shell.
<lang Phix>#!/bin/bash
sed -n -e '7,$p' < "$0" > tmp.eu
|
Revision as of 17:10, 31 January 2022
Simple shebangs can help with scripting, e.g., #!/usr/bin/env python
at the top of a Python script will allow it to be run in a terminal as "./script.py
".
Occasionally, a more complex shebang line is needed. For example, some languages do not include the program name in ARGV; a multiline shebang can reorder the arguments so that the program name is included in ARGV.
The syntax for a multiline shebang is complicated. The shebang lines must be simultaneously commented away from the main language and revealed to some shell (perhaps Bash) so that they can be executed. In other words, Polyglots.
Warning: Using a multiline shebang of the form #!/bin/sh ... exec ... !#
will set the code's mimetype to text/x-shellscript
, which creates problems such as Emacs treating the file as a shell script, no matter which language and file extension it really uses.
- See also
- Native shebang - where the "program loaded" is of the actual native task language.
Ada
<lang Ada>#!/bin/bash sed -n -e '7,$p' < "$0" > mulshbang.adb gnatmake -q mulshbang ./mulshbang $* rm mulshbang* exit with Ada.Text_IO, Ada.Command_Line; -- first line of Ada program
procedure Mulshbang is
use Ada.Text_IO;
begin
Put_Line("Name: " & Ada.Command_Line.Command_Name); for I in 1 .. Ada.Command_Line.Argument_Count loop Put_Line(" Arg" & Integer'Image(I) & ": " & Ada.Command_Line.Argument(I)); end loop;
end Mulshbang;</lang>
- Output:
>./adamulshbang Name: ./mulshbang >./adamulshbang one two three Name: ./mulshbang Arg 1: one Arg 2: two Arg 3: three
C
#!/bin/bash sed -n -e '7,$p' < "$0" | /usr/bin/gcc -x c -o "$0.$$.out" - $0.$$.out "$0" "$@" STATUS=$? rm $0.$$.out exit $STATUS #include <stdio.h> int main(int argc, char **argv) { int i; for (i = 0; i < argc; i++) printf("argv[%d] -> %s\n", i, argv[i]); return 0; }
Test runs:
$ ./cmulshbang.c argv[0] -> ./cmulshbang.c.4062.out argv[1] -> ./cmulshbang.c $ ./cmulshbang.c 1 argv[0] -> ./cmulshbang.c.4071.out argv[1] -> ./cmulshbang.c argv[2] -> 1 $ ./cmulshbang.c 1 2 argv[0] -> ./cmulshbang.c.4080.out argv[1] -> ./cmulshbang.c argv[2] -> 1 argv[3] -> 2
Student exercise: use a stable filename for the executable, e.g. "$0.out"
. Do not remove it, and only recompile it if the script's timestamp is newer than that of the executable.
Clojure
The namespace = basename = filename minus the extension must be passed as a value to Clojure's -m flag.
<lang clojure>":";exec clj -m `basename $0 .clj` $0 ${1+"$@"}</lang>
Alternate shebang, using the Leiningen 'exec' plugin:
<lang clojure>":";exec lein exec $0 ${1+"$@"}</lang>
Common Lisp
Here, the script name is passed once to CLISP and once to ext:*args*, which normally omits it.
<lang lisp>#!/bin/sh
- |
exec clisp -q -q $0 $0 ${1+"$@"} |#</lang>
E
E uses only “#” for line comments, like the shell, so there is no straightforward answer. We can abuse the fact that “>” is also a line comment to achieve this effect. Note that a “>” line comment should ordinarily only occur as part of Updoc (test/documentation) text, so this is not good practice.
In this example, we are including the command name itself in the argument list, which would ordinarily not include it.
<lang e>#!/bin/sh >/dev/null; exec rune $0 $0 ${1+"$@"}
println(`I was called as ${interp.getArgs()[0]}.`)</lang>
Emacs Lisp
<lang lisp>:;exec emacs -batch -l $0 -f main $*</lang>
Erlang
hello.erl
<lang Erlang>#!/usr/bin/env escript
-module(hello). -export([main/1]).
main(_) -> io:format("Hello World!~n", []).</lang>
This works fine when the module is run by itself with dot slash:
<lang sh>$ ./hello.erl Hello World!</lang>
But when another Erlang module tries to import the code, or you try to compile manually in erl, you get a syntax error.
<lang sh>$ erl Erlang R14B03 (erts-5.8.4) [source] [64-bit] [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false]
Eshell V5.8.4 (abort with ^G) 1> c(hello). ./hello.erl:1: syntax error before: '#' ./hello.erl:4: no module definition error</lang>
F#
F# scripts may be run with dot-slash notation using the following multiline shebang:
<lang f#>#light (* exec fsharpi --exec "$0" --quiet
- )
let main = printfn "Hello World"</lang>
However, if a script has any dependencies that need to be compiled in, the fsharpi interpreter will not understand how to import them. This means dot-slashing is no longer viable, and the script must be compiled in order to run properly. The shebang can stay, but it is best to remove it, to make clear to users that the script should not be dot-slashed.
Factor
Factor no longer requires a space after #!
as of v0.95.
<lang factor>#!/usr/bin/env factor -script</lang>
Forth
We can use Gforth's (non-ANS standard) support for shebangs and the '#' number prefix to make Gforth skip over the shebang without interfering with shell script interpretation.
<lang forth>#! /bin/sh
- 0 [IF] \ lines below read by shell but ignored by Gforth
exec gforth \ -m 256M \ -d 16M \ "$0" "$@"
[THEN] .( hello world) CR BYE </lang>
Go
<lang go>#!/bin/bash sed -n -e '12,$p' < "$0" > ttmmpp.go go build ttmmpp.go rm ttmmpp.go binfile="${0%.*}" mv ttmmpp $binfile $binfile "$@" STATUS=$? rm $binfile exit $STATUS
- Go Code start on line 12
package main import (
"fmt" "os"
)
func main() {
for i, x := range os.Args { if i == 0 { fmt.Printf("This program is named %s.\n", x) } else { fmt.Printf("the argument #%d is %s\n", i, x) } }
} </lang>
Groovy
<lang groovy>#!/bin/bash script_dir="$(cd $(dirname $0) >/dev/null; pwd -P)"
if [ -z "${GROOVY_HOME}" ] then
echo 'GROOVY_HOME must be defined.' >&2 exit 1
fi
CLASSPATH="${script_dir}" "${GROOVY_HOME}/bin/groovy" -e "$(sed -e '1,/^!#$/d' $0)" "${@:1}" exit !# println 'aoeu' </lang>
Haskell
<lang Haskell>#!/bin/bash sed -n -e '7,$p' < "$0" > $0.$$.hs ghc $0.$$.hs > /dev/null ./$0.$$ "$0" "$@" rm $0.$$* exit import Text.Printf import System.Environment
main :: IO () main = getArgs >>= mapM_ (uncurry $ printf "argv[%d] -> %s\n") . zip ([0..] :: [Int])</lang>
- Output:
$ ./multibang.hs argv[0] -> ./multibang.hs $ ./multibang.hs Goodbye, World! argv[0] -> ./multibang.hs argv[1] -> Goodbye, argv[2] -> World!
Or you can 'cheat' by ignoring Bash's complaints about Haskell comments (gives the exact same output as above):
<lang Haskell>#!/bin/bash {- 2> /dev/null exec runghc $0 $0 $@ -} import Text.Printf import System.Environment
main :: IO () main = getArgs >>= mapM_ (uncurry $ printf "argv[%d] -> %s\n") . zip ([0..] :: [Int])</lang>
J
Assuming this task is asking for a mix of unix shell commands and J, and also that the J binary directory is listed in $PATH
<lang J>#!/bin/sh
- 0 :0
echo unix shell commands go here echo presumably this will condition the environment echo for example: cd working-directory echo or maybe you want to modify $PATH, ... whatever... echo then start up J: exec jconsole "$0" "$@"
)
NB. exit on error onfail_z_=:3 :0
1!:2&2 ARGV 1!:2&2]13!:12 NB. display error message 2!:55>:13!:11 NB. exit with 1 origin error number
) 9!:27 'onfail 1' 9!:29]1
NB. and then the rest of the file is J echo 'hi!' echo 'your command line arguments were:' echo ARGV echo p:i. 3 4 exit 0 </lang>
Notes:
The #!/bin/sh
line is interpreted by J as a verb train with no arguments - in other words, it is ignored.
The # 0 :0
line is interpreted by shell as a comment and by J as the beginning of a multiline "hereis" script which basically ignores everything up to the lone right parenthesis.
So then it's just regular shell script up until the line where we turn control over to J. On that line, we use exec
(so that the shell process does not hang around, waiting for J to finish - J takes over the current process). And we pass any shell script command line arguments on to J.
On the J side of the fence, we presumably want this code to behave like a normal unix module, so we need to override J's default behavior (which is to provide the J command line). 9!:29]1[9!:27'2!:55]1
is a bit of magic that accomplishes that: it stacks a command to exit with exit code 1 to be executed when we reach the command line. So any errors will terminate the program.
Next, we run the system J profile so that we have all of the standard stuff that that provides. (Or leave this out if that's what you want.)
Finally we do some J stuff and then exit. If everything goes right, the command line exit we stacked earlier just gets ignored.
Here's a variant where the shell script tests J's exit code and does something different based on success or failure.
<lang J>#!/bin/sh
- 0 :0
echo unix shell commands go here echo presumably this will condition the environment echo for example: cd working-directory echo or maybe you want to modify $PATH, ... whatever... echo then start up J: if jconsole -jprofile "$0" "$@"; then echo success else echo failure fi exit $?
)
9!:29]1[9!:27'2!:55]1' NB. exit on error (3 :'0!:0 y')<BINPATH,'/profile.ijs'
NB. and then the rest of the file is J echo 'hi!' echo 'your command line arguments were:' echo ARGV echo p:i. 3 4 exit 0 </lang>
The exit $?
line tells the shell interpreter to ignore the J part of the file, and the $?
reuses J's exit code as the exit code from the shell instance.
Note that we've left off the onfail handler within J, and just used a minimal definition to give us a non-zero exit code for the error case. Mostly, the assumption here would be that the error message would not be interesting, and that any failure should be handled by a retry. But you could replace the exit on error line here with the full definition and 9!:
preparatory bit from the previous example and you could also of course change the 1!:2&2
lines (1!:2&2
is the "low-level" write to stdout mechanism for J - and, yes, those numbers are part of the definition of the language - or at least the "Foreigns" part of the language - note that ultimately all computer languages resolve to things which can be thought of as numbers or sequences of numbers, though some people will vigorously assert other things).
Julia
<lang julia>
- !/bin/sh
- =
echo Julia will ignore as commented all text between #= and =# echo which allows us to place arbitrary unix shell code here echo perhaps to change environment settings for Julia or echo set the directory prior to starting the Julia program. echo for example: cd /user/meeting/working echo then start the Julia program exec julia "$0" "$@"
- comments ignored by Julia end here --> =#
function countto(n)
i = zero(n) println("Counting to $n...") while i < n i += 1 end println("Done!")
end
@time countto(10^10) </lang>
MATLAB
Unlike Octave, MATLAB has no built-in support for shebangs. In fact, several tricks are required to even approximate a shebang, due to the byzantine way that MATLAB structures scripts and function files.
~/bin/shmatlab%:
<lang bash>#!/bin/sh matlab -nojvm -nodisplay -nosplash -r "varargin = regexp('${1+"$@"}', ' ', 'split'); nvarargin = length(varargin); run('$1'); exit" | tail -n +16 </lang>
args.m:
<lang matlab>'shmatlab'% $0 ${1+"$@"} 'exit';
for i = 1:nvarargin
disp(varargin{i});
end</lang>
Example:
$ ./args.m a b c ./args.m a b c
Nim
In Nim, multiline comments start with #[
and end with ]#
. This allows to build a polyglot program which can be run as a shell script and compiled as a Nim program.
<lang Nim>#!/bin/bash
- [
echo Put here code to run as a shell script. exit # This is needed to ignore last part of the file. ]#
- Nim program
echo "Executing Nim program"</lang>
OCaml
ocamlc hates shebangs, so much trickery is needed. The number of underscores in the dummy kkkk identifier corresponds to the number of bash strings in the shebang. Thus, core library .cma files can be specified this way in interpreted mode, though accessing other OCaml scripts requires compiling them first, and referencing the .cmo's here.
<lang ocaml>if true then ignore begin let kkkk _ _ _ _ = 0 in kkkk "exec" "ocaml" "$0" "$@" + let fi = 0 and exit _ _ = 0 in if false then exit fi true else 0 end;;
let main = print_endline "Hello World!"</lang>
Example:
$ head -n 2 she.ml if true then ignore begin let kkkk _ _ _ _ _ _ = 0 in kkkk "exec" "ocaml" "$0" "unix.cma" "graphics.cma" "$@" + let fi = 0 and exit _ _ = 0 in if false $ ocaml she.ml Hello World! $ /bin/bash she.ml Hello World! $ ocamlc -o she.byte she.ml $ ./she.byte Hello World! $ ocamlopt -o she.opt she.ml $ ./she.opt Hello World!
PARI/GP
The PARI equivalent to a multiline shebang is a collection of GP;
lines:
<lang C>/*
GP;install("C_function_name","G","GP_name","./filename.gp.so");
GP;addhelp(GP_name, "GP_name(n): Computes the foo of bar(n).");
- /</lang>
These commands are passed to GP when invoked by gp2c.
Perl
From perldoc perlrun
, the following is supposed to find perl one way or another under sh, csh or perl.
<lang perl>#!/usr/bin/perl
eval '(exit $?0)' && eval 'exec perl -wS $0 ${1+"$@"}'
& eval 'exec /usr/bin/perl -wS $0 $argv:q'
if $running_under_some_shell;</lang>
Phix
Obviously this is not pwa/p2js compatible, since you cannot run bash or sed (with redirection) or phix or 'rm tmp.eu' from within a browser, and is only intended to be run on Linux, though you could perhaps run it on Windows but only in some kind of bash shell. <lang Phix>#!/bin/bash sed -n -e '7,$p' < "$0" > tmp.eu \path\to\phix tmp.eu "$@" STATUS=$? rm tmp.eu exit $STATUS ?command_line()</lang>
PicoLisp
We can use a multi-line comment #{ ... }# to hide the shell commands from Lisp. The opening #{ in turn is a coment for the shell. <lang PicoLisp>#!/bin/bash
- {
exec pil $0 foo bar
- }#
- Lisp code
(println (cadr (file)) (opt) (opt)) (bye)</lang>
- Output:
$ ./myScript "myScript" "foo" "bar"
Pike
we use a multiline comment to hide the shell command from pike, and we can use a preprocessor directive to hide the comment begin from the shell. <lang Pike>#!/bin/bash
- define foo foo /*
exec pike $0 hello world
- /
int main(int argc, array argv) {
write("%O\n", argv);
}</lang>
- Output:
({ /* 3 elements */ "/local/users/mbaehr/src/pike/multiline-shebang/multiline-shebang.pike", "hello", "world" })
PostgreSQL
This style of shebang would also work with other languages that use double dashes for comments, though most of them (Lua, Haskell) already support traditional #!... shebangs.
<lang postgresql>--() { :; }; exec psql -f "$0"
SELECT 'Hello World!';</lang>
Python
We can use multiple strings to make the shell commands do nothing from Python (actually they become the module docstring.). <lang Python>#!/bin/bash "exec" "python" "$0"
print "Hello World"</lang>
- Output:
$ ./myScript Hello World
Control structures (if/for/etc.) can't be quoted, but one can use the following to embed any script: <lang Python>#!/bin/sh "true" \' if [ -L $0 ]; then ... exec "$interpreter" "$@" exit 127
__doc__ = """module docstring"""
print "Hello World"</lang>
Here we use a) the code '''\' translates to \ in shell, but opens a multi-line string in Python; b) the true command ignores its argument, c) we always exit before the ending ''' so that the shell interpreter never reads it. Also, remember to set any docstrings by assigning to __doc__ since the docstring is already used for the shell script.
Racket
<lang Racket>
- !/bin/sh
- | -*- scheme -*-
- this is sh code
echo running "$0", passing it into itself as an argument exec racket -tm "$0" "$0" |#
- lang racket
(provide main) (define (main arg)
(printf "argument: ~a\nexecuted as: ~a\n" arg (find-system-path 'exec-file)))
</lang>
Raku
(formerly Perl 6)
<lang perl6>#!/usr/local/bin/raku use MONKEY; EVAL '(exit $?0)' && EVAL 'exec rake $0 ${1+"$@"}' & EVAL 'exec raku $0 $argv:q'
if 0;</lang>
Ruby
One can use a single-line shebang, like #!/usr/bin/env ruby
,
and use Kernel#system or `backquotes` to run any extra shell commands.
A multi-line shebang is possible, but not necessary.
This script works both ways: either /bin/sh script.rb
or ruby script.rb
would run multiple lines of shell commands, and then start Ruby.
<lang ruby>#!/bin/sh
- Insert shell code here!
printf '%s\n' "Shell running $0" i=1 for arg do
printf ' %s\n' "\${$i}: $arg" i=`expr $i + 1`
done
- Switch from shell to Ruby.
exec ${RUBY-ruby} -x "$0" --coming-from-sh "$@"
- !ruby
ARGV[0] == "--coming-from-sh" or exec "/bin/sh", $0, *ARGV ARGV.shift
- Insert Ruby code here!
puts "Ruby running #$0" ARGV.each_with_index do |arg, i|
puts " ARGV[#{i}]: #{arg}"
end</lang>
When running /bin/sh scratch.rb
, the shell:
- ignores
#!/bin/sh
, because it is a comment. - runs multiple lines of shell code.
- executes
ruby -x
; user can set RUBY environment variable to pick different Ruby, like RUBY=ruby19 or RUBY=jruby.
ruby -x
skips every line until the first Ruby shebang. This line must start with "#!" and must contain "ruby". (So "#!ruby" is the shortest shebang to work.)
When running ruby scratch.rb
(without -x option), Ruby notices that the first line "#!/bin/sh" is a foreign shebang.
- Ruby 1.8 then interprets this shebang and executes /bin/sh.
- Ruby 1.9 then assumes -x option and skips to the first Ruby shebang. The script is not
--coming-from-sh
, so it executes /bin/sh.
Scala
The scala(1) interpreter parses a header section. The scalac compiler does not.
<lang scala>
- !/bin/bash
FOO=bar scala $0 $@ exit !# def fact(n : Int) : Int = {
var i = n ; var a = 1 ; while (i > 0) { a = a*i ; i -= 1 ; } return a ;
}
println("fact(5) = " + fact(5));</lang>
Scheme
<lang scheme>#!/usr/bin/env csi -ss</lang>
Sidef
<lang ruby>#!/bin/sh
- `(if running under some shell) {
eval 'exec /usr/bin/sidef $0 ${1+"$@"} "world"'
}
say "Hello, #{ARGV[0]}!"</lang>
- Output:
$ ./script.sf Hello, world! $ ./script.sf Sidef Hello, Sidef! $ sidef script.sf RosettaCode Hello, RosettaCode!
Smalltalk
<lang smalltalk>"exec" "gst" "-f" "$0" "$0" "$@"</lang>
SQL PL
Based on the Postgres shebang, it works the same with IBM Db2.
<lang sql pl> --() { :; }; exec db2 -txf "$0"
get instance; connect to sample; select 'Hello' from sysibm.sysdummy1; values current date; </lang> Output:
$ ./myScript The current database manager instance is: db2inst1 Database Connection Information Database server = DB2/LINUXX8664 11.1.1 SQL authorization ID = DB2INST1 Local database alias = SAMPLE Hello 04/22/2018
The db2profile should be loaded before executing the 'db2' command (. ~db2inst1/sqllib/db2profile).
The options used in the example are: t - delimited by semi colon, x - Suppress printing of column headings, f - Read from input file. For other options, you can execute 'db2 ? options', and change the shebang.
Tcl
It is normal to use a line like this: <lang tcl>#!/usr/bin/env tclsh</lang> But in cases where that is not enough perhaps because it needs some logic to locate the Tcl interpreter to use the differences in the way Tcl and the Bourne shell interpret end-of-line backslashes in comments can be used: <lang tcl>#!/bin/sh
- Next line is comment in Tcl, but not in sh... \
exec tclsh "$0" ${1+"$@"}</lang> Additional complexity can be added so long as the lines for the shell are commented in a Tcl sense.
TXR
#!/bin/sh sed -n -e '4,$p' < "$0" | /usr/bin/txr -B - "$0" "$@" exit $? @(next :args) @(collect) @arg @(end)
Test run:
$ ./multilineshebang.txr arg[0]="./multilineshebang.txr" $ ./multilineshebang.txr 1 arg[0]="./multilineshebang.txr" arg[1]="1" $ ./multilineshebang.txr 1 2 3 arg[0]="./multilineshebang.txr" arg[1]="1" arg[2]="2" arg[3]="3" $
Wren
Wren doesn't support multiline shebangs as such. Anything after the first line is always interpreted as Wren code.
You can get around this by placing shell commands in a block comment after a single line shebang. So (ignoring the strange error message) the following works: <lang ecmascript>#!/bin/bash /* echo "Hello from bash" /bin/wren multiline_shebang.wren exit
- /
System.print("Hello from Wren")</lang>
- Output:
$ chmod +x multiline_shebang.wren $ ./multiline_shebang.wren ./multiline_shebang.wren: line 2: /bin: Is a directory Hello from bash Hello from Wren
However, we don't actually need a multiline shebang to get the script name as this is always passed automatically as the second command line argument when the Wren process is spawned, the first argument being the Wren executable itself. Moreover, if a single line shebang is used, the third argument will be the shell command used to execute the script.
<lang ecmascript>#!/bin/wren multiline_shebang.wren
import "os" for Process
var args = Process.allArguments System.print("Executable : %(args[0])") System.print("Script name : %(args[1])") System.print("Shell command : %(args[2])") if (args.count > 3) {
for (i in 3...args.count) System.print("Argument %(i-2) : %(args[i])")
}</lang>
- Output:
$ ./multiline_shebang.wren one two three Executable : /bin/wren Script name : multiline_shebang.wren Shell command : ./multiline_shebang.wren Argument 1 : one Argument 2 : two Argument 3 : three
zkl
zkl has a variant of the here doc that means ignore the doc, as in "#if 0" but more so. But that doesn't mean a shell has to ignore it.
File foo.zkl (the .zkl extension is needed): <lang zkl>#!/bin/sh
- <<<#
echo "A shell script in a zkl program ($0)" echo "Now run zkl <this file> with Hello World as args" zkl $0 Hello World! exit
- <<<#
println("The shell script says ",vm.arglist.concat(" "));</lang>
- Output:
$ ./foo.zkl A shell script in a zkl program (./foo.zkl) Now run zkl <this file> with Hello World as args The shell script says Hello World! $
- Draft Programming Tasks
- Basic language learning
- Ada
- C
- Clojure
- Common Lisp
- E
- Emacs Lisp
- Erlang
- F Sharp
- Factor
- Forth
- Go
- Groovy
- Haskell
- J
- Julia
- MATLAB
- Nim
- OCaml
- PARI/GP
- Perl
- Phix
- PicoLisp
- Pike
- PostgreSQL
- Python
- Racket
- Raku
- Ruby
- Scala
- Scheme
- Sidef
- Smalltalk
- SQL PL
- Tcl
- TXR
- Wren
- Zkl
- BASIC/Omit
- BBC BASIC/Omit
- Blast/Omit
- Brlcad/Omit
- GUISS/Omit
- Locomotive Basic/Omit
- Nemerle/Omit
- Openscad/Omit
- Z80A/Omit
- ZX Spectrum Basic/Omit