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I think the Shebang thing, although valid, is a red herring.

Other things may happen:

Bad interpreter, i.e. the program after #! could not be found. The Mac error message is at least similar.

/tmp>cat #!/no/such/perl -w use strict; use warnings; print 'Hello\n'; /tmp>chmod +x /tmp>./ -bash: ./ /no/such/perl: bad interpreter: No such file or d +irectory /tmp>

Interpreter not executable:

/tmp>cat #!/etc/passwd use strict; use warnings; print 'Hello\n';pstree -al /tmp>chmod +x /tmp>./ -bash: ./ /etc/passwd: bad interpreter: Permission denied /tmp>

Shebang not identified as such:

/tmp>cat #!/usr/bin/perl -w # ^- note: Shebang on second line, first line is empty! use strict; use warnings; print 'Hello\n'; /tmp>chmod +x /tmp>./ ./ line 5: use: command not found ./ line 6: use: command not found ./ line 8: print: command not found /tmp>

This also happens when there is an (invisible) Byte Order Mark (BOM) at the start of the file. What happens here?

The shell attempts to start ./ via fork() and exec(), as usual. This will fail, because the kernel can't identify the file as binary executable or script with some interpreter (first two bytes aren't #!). At this point, a legacy mechanism in the shell kicks in. In the very early days of Unix, shell scripts did not have to have the shebang. If you chmod +x any text file and try to run it, but exec() fails, the shell will attempt to read it as a shell script. A little experiment shows this:

/tmp>echo 'pstree -Aal' >> /tmp>./ ./ line 5: use: command not found ./ line 6: use: command not found ./ line 8: print: command not found init . . . |-sshd | `-sshd | `-sshd | `-bash | `-bash | `-pstree -Aal . . .


A little trick to ensure you don't run into the BOM trap:

/tmp>perl -e '$_=<STDIN>;print ord $_' < 10 /tmp>

This test must return 35 or the script does not start with the shebang. 10 is a LF, the end of the first line. 13 is CR, the end of the first line with MS-DOS or classic Mac line-endings, 32 is a space, 9 is a tab. Byte Order Marks may show up as 239 (UTF-8), 254 (UTF-16 BE), 255 (UTF-16 LE or UTF-32 LE), 0 (UTF-32 BE), 43 (UTF-7), 247 (UTF-1).


See also Re^2: Shebang behavior with perl


Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

In reply to Re^2: open and read text file by afoken
in thread open and read text file by hchana

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