Re: bash scripts and files
michael wrote: On Wed, 2008-01-09 at 13:26 +0100, Dan H wrote: On Wed, 09 Jan 2008 12:03:07 + michael <[EMAIL PROTECTED]> wrote: .bashrc and .bash_profile are different. They are only reasonably invoked by a bash shell, so it is safe to assume they are written using bash syntax. They are, after all, configuration files for bash, so what other language would they be written in? "reasonably"?! and where is it stated they are different? surely they should have the !# at the start too it's this implicitness that upsets me! They aren't even executable, so why should they have hash-bang? aha, now that's a very good point! and perhaps the clearest reason: scripts are executable and require hash-bang (strictly they don't have to have that but it's useful to ensure they will run if they contain shell specifics) files associated with the innovation of a shell (such as .bashrc, .cshrc, .bash_profile) are not shells and are not executable and thus do not require hash-bang M This is just the tip of the iceberg, that is to say, the subject is a bit complex, requiring some knowledge of system calls, and history. So this will be a bit long. UNIX/Linux systems use the fork/exec system calls to handle execution of a program (binary executable). A shell will fork a copy of itself, the copy gets a new PID but is otherwise the same as the parent. The copy (child) then uses exec to overlay itself with the new program code. But, if the program code is a shell script, the exec will return an error, which the shell will detect. The child shell will then try to read the file as text, treating it as a shell script. Two things to note in the above: there is no way for what is found in the file and executed in the child, to pollute the parent; and the shell simply assumes the syntax is correct. The script may be as simple as one line, invoking some other command (awk, sed, chmod) with arguments (this is how non-shell scripts were usually handled before hash/bang was invented). Start up files need to pollute the shell, so they must be sourced. This happens automatically for the start up files the shell knows about, and can be done manually by the user, using the 'dot' (.) or 'source' command, depending on the shell in use. In the case of sourcing, just as for the case with the failed exec, above, the shell assumes the file format is its own. And, sourced files do *not* need to be made executable. Technically, scripts don't either, you can run them as 'shell script' without doing a chmod. Now, the history. This rounds out the picture, but is not really necessary for understanding startup scripts. The original UNIX shell was a loner, there were no other shells, so just reading the file and running the commands was enough. But then came the C shell and it had different syntax. So, the C shell had an extra bit added to it. Reading the first line, if it has a single character and that character is a colon, then the file is not a C shell script, exec a "standard" shell to run it. Otherwise, treat it as a C shell script. And this worked fine, for a time. But then there were awk and sed, then Perl, Python, and so on. And an easier way was needed to make scripts with these languages work. The standard, with awk and sed, started out to be writing a file with the script, and running awk or sed with an option and script file name, similar to using 'shell script'. But that wasn't good enough, too much typing. So the exec system call was modified to deal with scripts directly. It will read the first two characters of the executable file and if they are hash/bang, it will use the rest of the line to find the actual file to exec, passing that program the name of the script with any arguments. -- Bob McGowan smime.p7s Description: S/MIME Cryptographic Signature
Re: bash scripts and files
On Wed, 2008-01-09 at 13:26 +0100, Dan H wrote: > On Wed, 09 Jan 2008 12:03:07 + > michael <[EMAIL PROTECTED]> wrote: > > > > .bashrc and .bash_profile are different. They are only reasonably > > > invoked by a bash shell, so it is safe to assume they are written > > > using bash syntax. They are, after all, configuration files for > > > bash, so what other language would they be written in? > > > > "reasonably"?! > > and where is it stated they are different? > > surely they should have the !# at the start too > > it's this implicitness that upsets me! > > They aren't even executable, so why should they have hash-bang? aha, now that's a very good point! and perhaps the clearest reason: scripts are executable and require hash-bang (strictly they don't have to have that but it's useful to ensure they will run if they contain shell specifics) files associated with the innovation of a shell (such as .bashrc, .cshrc, .bash_profile) are not shells and are not executable and thus do not require hash-bang M -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
Re: bash scripts and files
On Wed, 09 Jan 2008 12:03:07 + michael <[EMAIL PROTECTED]> wrote: > > .bashrc and .bash_profile are different. They are only reasonably > > invoked by a bash shell, so it is safe to assume they are written > > using bash syntax. They are, after all, configuration files for > > bash, so what other language would they be written in? > > "reasonably"?! > and where is it stated they are different? > surely they should have the !# at the start too > it's this implicitness that upsets me! They aren't even executable, so why should they have hash-bang? --D. -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
Re: bash scripts and files
On Mon, 2007-12-31 at 18:51 +, Tyler Smith wrote:
> On 2007-12-31, michael <[EMAIL PROTECTED]> wrote:
> >
> > Thanks, probably the previous chapter ("she-bang") was of more use
> > but a useful ref. However, I'm still trying to understand why it's
> > not usual to have a she-bang for the .bash_profile and .bashrc files.
> > That documentation reads as if it's expected - they are scripts and
> > contain shell specific syntax.
>
> Regular shell scripts could be called from any number of places. If
> you're running a bash shell, you could run a csh or zsh or python
> script. Similarly any of these scripts could be called from another
> process, such as from a program written in C, or Lisp, or whatever. In
> any of these cases the language of the script has no relation to the
> environment it is called from. All the caller knows is that they are
> executable files - any details are hidden. That means the pertinent
> information needs to be stored in the script itself, and that has to
> happen on the first line so the proper interpreter is invoked.
>
> Imagine what would happen if you didn't do this. You call a script
> from your terminal running bash, and that script is written in Perl.
> Without the #! the terminal could either assume it's written in bash,
> and choke on the syntax, or try and guess the language, which gets
> hairy very quickly.
Yes, all this I understand and appreciate
>
> .bashrc and .bash_profile are different. They are only reasonably
> invoked by a bash shell, so it is safe to assume they are written
> using bash syntax. They are, after all, configuration files for bash,
> so what other language would they be written in?
"reasonably"?!
and where is it stated they are different?
surely they should have the !# at the start too
it's this implicitness that upsets me!
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Re: bash scripts and files
On 2007-12-31, michael <[EMAIL PROTECTED]> wrote:
>
> Thanks, probably the previous chapter ("she-bang") was of more use
> but a useful ref. However, I'm still trying to understand why it's
> not usual to have a she-bang for the .bash_profile and .bashrc files.
> That documentation reads as if it's expected - they are scripts and
> contain shell specific syntax.
Regular shell scripts could be called from any number of places. If
you're running a bash shell, you could run a csh or zsh or python
script. Similarly any of these scripts could be called from another
process, such as from a program written in C, or Lisp, or whatever. In
any of these cases the language of the script has no relation to the
environment it is called from. All the caller knows is that they are
executable files - any details are hidden. That means the pertinent
information needs to be stored in the script itself, and that has to
happen on the first line so the proper interpreter is invoked.
Imagine what would happen if you didn't do this. You call a script
from your terminal running bash, and that script is written in Perl.
Without the #! the terminal could either assume it's written in bash,
and choke on the syntax, or try and guess the language, which gets
hairy very quickly.
.bashrc and .bash_profile are different. They are only reasonably
invoked by a bash shell, so it is safe to assume they are written
using bash syntax. They are, after all, configuration files for bash,
so what other language would they be written in?
HTH,
Tyler
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Re: bash scripts and files
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Hash: SHA1
On 12/31/07 05:07, michael wrote:
>
> On 30 Dec 2007, at 18:11, Gerard Robin wrote:
>
>> On Sun, Dec 30, 2007 at 05:17:43PM +, michael wrote:
>>> From: michael <[EMAIL PROTECTED]>
>>> To: debian user
>>> Subject: bash scripts and files
>>>
>>> Folks, can somebody point me to an authorative reference that
>>> explains when one needs to put, eg,
>>> #!/bin/bash
>>> as the first line of a script and whether or not it's
>>> required/surplus/ignored for bash specific files such as .bashrc and
>>> .bash_profile
>> have look at:
>> http://tldp.org/LDP/abs/html/invoking.html
>> The whole tutorial is in the package: abs-guide
>
> Thanks, probably the previous chapter ("she-bang") was of more use but a
> useful ref. However, I'm still trying to understand why it's not usual
> to have a she-bang for the .bash_profile and .bashrc files. That
> documentation reads as if it's expected - they are scripts and contain
> shell specific syntax.
Probably because those files are "sourced" from within another
process instead of directly executable from the command line.
- --
Ron Johnson, Jr.
Jefferson LA USA
"Your mistletoe is no match for my TOW missile." Santa-bot
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Re: bash scripts and files
On 30 Dec 2007, at 18:11, Gerard Robin wrote:
On Sun, Dec 30, 2007 at 05:17:43PM +, michael wrote:
From: michael <[EMAIL PROTECTED]>
To: debian user
Subject: bash scripts and files
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Folks, can somebody point me to an authorative reference that
explains when one needs to put, eg,
#!/bin/bash
as the first line of a script and whether or not it's required/
surplus/ignored for bash specific files such as .bashrc
and .bash_profile
have look at:
http://tldp.org/LDP/abs/html/invoking.html
The whole tutorial is in the package: abs-guide
Thanks, probably the previous chapter ("she-bang") was of more use
but a useful ref. However, I'm still trying to understand why it's
not usual to have a she-bang for the .bash_profile and .bashrc files.
That documentation reads as if it's expected - they are scripts and
contain shell specific syntax.
Thanks, Michael
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Re: bash scripts and files
On Sun, Dec 30, 2007 at 05:17:43PM +, michael wrote: From: michael <[EMAIL PROTECTED]> To: debian user Subject: bash scripts and files X-Spam-Virus: No X-Spam-Checker-Version: SpamAssassin 3.2.3 (2007-08-08) on liszt.debian.org X-Spam-Level: X-Spam-Status: No, score=-6.6 required=4.0 tests=AWL,LDO_WHITELIST, RCVD_IN_DNSWL_MED autolearn=failed version=3.2.3 X-Mailer: Apple Mail (2.752.3) Folks, can somebody point me to an authorative reference that explains when one needs to put, eg, #!/bin/bash as the first line of a script and whether or not it's required/surplus/ignored for bash specific files such as .bashrc and .bash_profile have look at: http://tldp.org/LDP/abs/html/invoking.html The whole tutorial is in the package: abs-guide hth. -- Gérard
Re: bash scripts and files
2007/12/30, michael <[EMAIL PROTECTED]>: > Folks, can somebody point me to an authorative reference that > explains when one needs to put, eg, > #!/bin/bash > as the first line of a script and whether or not it's required/ > surplus/ignored for bash specific files such as .bashrc > and .bash_profile > > many thanks but couldn't find it quickly using 'oogle. M In a script that line specifies the interpreter to use to execute the following lines on the script. It may be any interpreter that you want: bash, sh, ksh, perl, python,etc.. In .bashrc, .bash_profile or other files that are "included" from other interpreter/scripts you dont need the interpreter line. As a note, if you are planning to write portable scripts, please use #!/bin/sh and avoid "bashism" (like [ $foo -ge 1 ]) in the syntax. Greetings -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
bash scripts and files
Folks, can somebody point me to an authorative reference that explains when one needs to put, eg, #!/bin/bash as the first line of a script and whether or not it's required/ surplus/ignored for bash specific files such as .bashrc and .bash_profile many thanks but couldn't find it quickly using 'oogle. M -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
