#!/usr/bin/env foo #!vs /usr/bin/foo [duplicate]

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  • Why is it better to use “#!/usr/bin/env NAME” instead of “#!/path/to/NAME” as my shebang?

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Which of the above forms is "better" for running bash, python etc. scripts? Why can't I just do #!$(which foo)? Is it neccecery to specify full path to env? I gather from this answer, that the path /usr/bin/env is set in stone for all *nix-es, much more than /usr/bin/python3 for example. Is that so?




scripting path shebang




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marked as duplicate by muru, Hunter.S.Thompson, peterh, jimmij, Raphael Ahrens Nov 19 '17 at 15:01


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    up vote
    0
    down vote

    favorite













    This question already has an answer here:



    • Why is it better to use “#!/usr/bin/env NAME” instead of “#!/path/to/NAME” as my shebang?

      9 answers



    Which of the above forms is "better" for running bash, python etc. scripts? Why can't I just do #!$(which foo)? Is it neccecery to specify full path to env? I gather from this answer, that the path /usr/bin/env is set in stone for all *nix-es, much more than /usr/bin/python3 for example. Is that so?




    scripting path shebang




    share|improve this question














    marked as duplicate by muru, Hunter.S.Thompson, peterh, jimmij, Raphael Ahrens Nov 19 '17 at 15:01


    This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
















      up vote
      0
      down vote

      favorite









      up vote
      0
      down vote

      favorite












      This question already has an answer here:



      • Why is it better to use “#!/usr/bin/env NAME” instead of “#!/path/to/NAME” as my shebang?

        9 answers



      Which of the above forms is "better" for running bash, python etc. scripts? Why can't I just do #!$(which foo)? Is it neccecery to specify full path to env? I gather from this answer, that the path /usr/bin/env is set in stone for all *nix-es, much more than /usr/bin/python3 for example. Is that so?




      scripting path shebang




      share|improve this question















      This question already has an answer here:



      • Why is it better to use “#!/usr/bin/env NAME” instead of “#!/path/to/NAME” as my shebang?

        9 answers



      Which of the above forms is "better" for running bash, python etc. scripts? Why can't I just do #!$(which foo)? Is it neccecery to specify full path to env? I gather from this answer, that the path /usr/bin/env is set in stone for all *nix-es, much more than /usr/bin/python3 for example. Is that so?





      This question already has an answer here:



      • Why is it better to use “#!/usr/bin/env NAME” instead of “#!/path/to/NAME” as my shebang?

        9 answers





      scripting path shebang





      share|improve this question













      share|improve this question




      share|improve this question








      edited Nov 19 '17 at 11:00









      Jeff Schaller

      32.1k849109




      32.1k849109










      asked Nov 19 '17 at 10:49









      Vorac

      94621732




      94621732




      marked as duplicate by muru, Hunter.S.Thompson, peterh, jimmij, Raphael Ahrens Nov 19 '17 at 15:01


      This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.






      marked as duplicate by muru, Hunter.S.Thompson, peterh, jimmij, Raphael Ahrens Nov 19 '17 at 15:01


      This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.






















          1 Answer
          1






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          1
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          You can’t just write #!$(which foo) because that line is interpreted by the kernel, which does not understand complex syntaxes like $().



          The kernel does not search for the command in the PATH environment variable. That’s why you have to specify the full path to the command.



          The use of /usr/bin/env is a clever hack used to search the command in the PATH. Even if there is a /usr/bin/python3 program, you may for example have installed a more recent version of Python in a different path, for example in you home directory.






          share|improve this answer




















          • Ahaa, so $() is a shell feature. As well as searching the path, consequently I can't just write #!python3. What about the cross-platform issue. Do we get /usr/bin/env on MacOS? FreeBSD? QNX?
            – Vorac
            Nov 19 '17 at 11:03










          • Searching the PATH is not exactly a shell feature; it is a libc feature. That’s only a guess, but /usr/bin/env might be required by the POSIX standard.
            – user2233709
            Nov 19 '17 at 11:13










          • You can't use #!$(which foo) because shell expansion does not occur for comments... as in #! (a comment)... This is by specific design. There is no "better" or "best" way to set your interpreter. I tend to use #!/usr/bin/env perl + #!/usr/bin/env ffmpeg, because I build these nightly, against latest source. So in general, you'll use /usr/bin/env when you have multiple copies of a program in your $PATH + you'd like to take the highest precedence version (one appearing first in your $PATH variable).
            – David Favor
            Nov 19 '17 at 13:01










          • @DavidFavor It does not matter that it’s a comment, it matters that it is a special kernel feature.
            – user2233709
            Nov 19 '17 at 13:08










          • @MarkPlotnick Are you sure it is a feature of the shell? I just gave it a try, and could also run that shell script through /usr/bin/env…
            – user2233709
            Nov 19 '17 at 14:23

















          1 Answer
          1






          active

          oldest

          votes








          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes








          up vote
          1
          down vote













          You can’t just write #!$(which foo) because that line is interpreted by the kernel, which does not understand complex syntaxes like $().



          The kernel does not search for the command in the PATH environment variable. That’s why you have to specify the full path to the command.



          The use of /usr/bin/env is a clever hack used to search the command in the PATH. Even if there is a /usr/bin/python3 program, you may for example have installed a more recent version of Python in a different path, for example in you home directory.






          share|improve this answer




















          • Ahaa, so $() is a shell feature. As well as searching the path, consequently I can't just write #!python3. What about the cross-platform issue. Do we get /usr/bin/env on MacOS? FreeBSD? QNX?
            – Vorac
            Nov 19 '17 at 11:03










          • Searching the PATH is not exactly a shell feature; it is a libc feature. That’s only a guess, but /usr/bin/env might be required by the POSIX standard.
            – user2233709
            Nov 19 '17 at 11:13










          • You can't use #!$(which foo) because shell expansion does not occur for comments... as in #! (a comment)... This is by specific design. There is no "better" or "best" way to set your interpreter. I tend to use #!/usr/bin/env perl + #!/usr/bin/env ffmpeg, because I build these nightly, against latest source. So in general, you'll use /usr/bin/env when you have multiple copies of a program in your $PATH + you'd like to take the highest precedence version (one appearing first in your $PATH variable).
            – David Favor
            Nov 19 '17 at 13:01










          • @DavidFavor It does not matter that it’s a comment, it matters that it is a special kernel feature.
            – user2233709
            Nov 19 '17 at 13:08










          • @MarkPlotnick Are you sure it is a feature of the shell? I just gave it a try, and could also run that shell script through /usr/bin/env…
            – user2233709
            Nov 19 '17 at 14:23














          up vote
          1
          down vote













          You can’t just write #!$(which foo) because that line is interpreted by the kernel, which does not understand complex syntaxes like $().



          The kernel does not search for the command in the PATH environment variable. That’s why you have to specify the full path to the command.



          The use of /usr/bin/env is a clever hack used to search the command in the PATH. Even if there is a /usr/bin/python3 program, you may for example have installed a more recent version of Python in a different path, for example in you home directory.






          share|improve this answer




















          • Ahaa, so $() is a shell feature. As well as searching the path, consequently I can't just write #!python3. What about the cross-platform issue. Do we get /usr/bin/env on MacOS? FreeBSD? QNX?
            – Vorac
            Nov 19 '17 at 11:03










          • Searching the PATH is not exactly a shell feature; it is a libc feature. That’s only a guess, but /usr/bin/env might be required by the POSIX standard.
            – user2233709
            Nov 19 '17 at 11:13










          • You can't use #!$(which foo) because shell expansion does not occur for comments... as in #! (a comment)... This is by specific design. There is no "better" or "best" way to set your interpreter. I tend to use #!/usr/bin/env perl + #!/usr/bin/env ffmpeg, because I build these nightly, against latest source. So in general, you'll use /usr/bin/env when you have multiple copies of a program in your $PATH + you'd like to take the highest precedence version (one appearing first in your $PATH variable).
            – David Favor
            Nov 19 '17 at 13:01










          • @DavidFavor It does not matter that it’s a comment, it matters that it is a special kernel feature.
            – user2233709
            Nov 19 '17 at 13:08










          • @MarkPlotnick Are you sure it is a feature of the shell? I just gave it a try, and could also run that shell script through /usr/bin/env…
            – user2233709
            Nov 19 '17 at 14:23












          up vote
          1
          down vote










          up vote
          1
          down vote









          You can’t just write #!$(which foo) because that line is interpreted by the kernel, which does not understand complex syntaxes like $().



          The kernel does not search for the command in the PATH environment variable. That’s why you have to specify the full path to the command.



          The use of /usr/bin/env is a clever hack used to search the command in the PATH. Even if there is a /usr/bin/python3 program, you may for example have installed a more recent version of Python in a different path, for example in you home directory.






          share|improve this answer












          You can’t just write #!$(which foo) because that line is interpreted by the kernel, which does not understand complex syntaxes like $().



          The kernel does not search for the command in the PATH environment variable. That’s why you have to specify the full path to the command.



          The use of /usr/bin/env is a clever hack used to search the command in the PATH. Even if there is a /usr/bin/python3 program, you may for example have installed a more recent version of Python in a different path, for example in you home directory.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Nov 19 '17 at 10:56









          user2233709

          603310




          603310











          • Ahaa, so $() is a shell feature. As well as searching the path, consequently I can't just write #!python3. What about the cross-platform issue. Do we get /usr/bin/env on MacOS? FreeBSD? QNX?
            – Vorac
            Nov 19 '17 at 11:03










          • Searching the PATH is not exactly a shell feature; it is a libc feature. That’s only a guess, but /usr/bin/env might be required by the POSIX standard.
            – user2233709
            Nov 19 '17 at 11:13










          • You can't use #!$(which foo) because shell expansion does not occur for comments... as in #! (a comment)... This is by specific design. There is no "better" or "best" way to set your interpreter. I tend to use #!/usr/bin/env perl + #!/usr/bin/env ffmpeg, because I build these nightly, against latest source. So in general, you'll use /usr/bin/env when you have multiple copies of a program in your $PATH + you'd like to take the highest precedence version (one appearing first in your $PATH variable).
            – David Favor
            Nov 19 '17 at 13:01










          • @DavidFavor It does not matter that it’s a comment, it matters that it is a special kernel feature.
            – user2233709
            Nov 19 '17 at 13:08










          • @MarkPlotnick Are you sure it is a feature of the shell? I just gave it a try, and could also run that shell script through /usr/bin/env…
            – user2233709
            Nov 19 '17 at 14:23
















          • Ahaa, so $() is a shell feature. As well as searching the path, consequently I can't just write #!python3. What about the cross-platform issue. Do we get /usr/bin/env on MacOS? FreeBSD? QNX?
            – Vorac
            Nov 19 '17 at 11:03










          • Searching the PATH is not exactly a shell feature; it is a libc feature. That’s only a guess, but /usr/bin/env might be required by the POSIX standard.
            – user2233709
            Nov 19 '17 at 11:13










          • You can't use #!$(which foo) because shell expansion does not occur for comments... as in #! (a comment)... This is by specific design. There is no "better" or "best" way to set your interpreter. I tend to use #!/usr/bin/env perl + #!/usr/bin/env ffmpeg, because I build these nightly, against latest source. So in general, you'll use /usr/bin/env when you have multiple copies of a program in your $PATH + you'd like to take the highest precedence version (one appearing first in your $PATH variable).
            – David Favor
            Nov 19 '17 at 13:01










          • @DavidFavor It does not matter that it’s a comment, it matters that it is a special kernel feature.
            – user2233709
            Nov 19 '17 at 13:08










          • @MarkPlotnick Are you sure it is a feature of the shell? I just gave it a try, and could also run that shell script through /usr/bin/env…
            – user2233709
            Nov 19 '17 at 14:23















          Ahaa, so $() is a shell feature. As well as searching the path, consequently I can't just write #!python3. What about the cross-platform issue. Do we get /usr/bin/env on MacOS? FreeBSD? QNX?
          – Vorac
          Nov 19 '17 at 11:03




          Ahaa, so $() is a shell feature. As well as searching the path, consequently I can't just write #!python3. What about the cross-platform issue. Do we get /usr/bin/env on MacOS? FreeBSD? QNX?
          – Vorac
          Nov 19 '17 at 11:03












          Searching the PATH is not exactly a shell feature; it is a libc feature. That’s only a guess, but /usr/bin/env might be required by the POSIX standard.
          – user2233709
          Nov 19 '17 at 11:13




          Searching the PATH is not exactly a shell feature; it is a libc feature. That’s only a guess, but /usr/bin/env might be required by the POSIX standard.
          – user2233709
          Nov 19 '17 at 11:13












          You can't use #!$(which foo) because shell expansion does not occur for comments... as in #! (a comment)... This is by specific design. There is no "better" or "best" way to set your interpreter. I tend to use #!/usr/bin/env perl + #!/usr/bin/env ffmpeg, because I build these nightly, against latest source. So in general, you'll use /usr/bin/env when you have multiple copies of a program in your $PATH + you'd like to take the highest precedence version (one appearing first in your $PATH variable).
          – David Favor
          Nov 19 '17 at 13:01




          You can't use #!$(which foo) because shell expansion does not occur for comments... as in #! (a comment)... This is by specific design. There is no "better" or "best" way to set your interpreter. I tend to use #!/usr/bin/env perl + #!/usr/bin/env ffmpeg, because I build these nightly, against latest source. So in general, you'll use /usr/bin/env when you have multiple copies of a program in your $PATH + you'd like to take the highest precedence version (one appearing first in your $PATH variable).
          – David Favor
          Nov 19 '17 at 13:01












          @DavidFavor It does not matter that it’s a comment, it matters that it is a special kernel feature.
          – user2233709
          Nov 19 '17 at 13:08




          @DavidFavor It does not matter that it’s a comment, it matters that it is a special kernel feature.
          – user2233709
          Nov 19 '17 at 13:08












          @MarkPlotnick Are you sure it is a feature of the shell? I just gave it a try, and could also run that shell script through /usr/bin/env…
          – user2233709
          Nov 19 '17 at 14:23




          @MarkPlotnick Are you sure it is a feature of the shell? I just gave it a try, and could also run that shell script through /usr/bin/env…
          – user2233709
          Nov 19 '17 at 14:23


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