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Re: Determine if a file is a valid Bash script


From: Eric Blake
Subject: Re: Determine if a file is a valid Bash script
Date: Mon, 19 Mar 2012 14:46:23 -0600
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On 03/19/2012 02:15 PM, Stefano Lattarini wrote:
> On 03/19/2012 08:54 PM, Lane Schwartz wrote:
>> Hi,
>>
>> If I have a file that contains a bash script, is there any
>> straightforward way of determining whether that script can be parsed
>> successfully as a Bash script, without actually running the file?
>>
> Yes: the "-n" option.  Simple examples:
> 
>   $ echo 'if :; then echo not seen; fi' | bash -n; echo status: $?
>   status: 0
>   $ echo 'if :; then echo not seen' | bash -n; echo status: $?
>   bash: line 2: syntax error: unexpected end of file
>   status: 2

Support for -n is required by POSIX for all sh-like shells.  But it
comes with some caveats - on Solaris 8, the implementation of '/bin/sh
-n' is extremely inefficient, and can take several minutes on complex
scripts.  And even older, on SunOS 4, you could make '/bin/sh -n' go
into an infinite loop on a script as simple a while loop that never
executes.  More recently, modern ksh '-n' warns about every suspicious
construct, such as complaining about `` instead of $().  And don't ever
try 'set -n' in an interactive script or in the middle of a shell, as
you can't use 'set +n' to turn it back off :)

-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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