I wonder why systems don't link /bin/sh to BASH rather than DASH by default if BASH is a better shell?
bash is no better (or worse) than dash - just different. Every UNIX system has some default shell, which you can reach under "/bin/sh". In many Linux-variants this is bash (RedHat-based variants, Slackware, ....), in some others (debian-based variants) it is dash, and in my beloved IBM AIX Unix it is a ksh88.
This is why you can specify explicitly by which shell your script should be run using the "shebang", as it is called: if the absolute first 2 bytes of an executable file are "#!" then the named executable following this is run and fed the following text as input.
Code:
#! /bin/bash
<... here comes some shell script...>
means: load "/bin/bash" and feed it the rest of the text as input. You can even force the system to use your own version if you want to try something with a special version you installed:
Code:
#! /my/private/version/of/bash
<... here comes some shell script...>
and you can specify any other executable as well, for instance awk:
Thank you, it's good to know the best practice. It's interesting that there is an error when using DASH, but no error when using BASH.
I wonder why systems don't link /bin/sh to BASH rather than DASH by default if BASH is a better shell?
dash may have less functionality than bash but it is a POSIX compliant and it is smaller and faster than bash, so systems startup scripts will run faster which leads to shorter boot times for example..
bash is no better (or worse) than dash - just different. Every UNIX system has some default shell, which you can reach under "/bin/sh". In many Linux-variants this is bash (RedHat-based variants, Slackware, ....), in some others (debian-based variants) it is dash, and in my beloved IBM AIX Unix it is a ksh88.
This is why you can specify explicitly by which shell your script should be run using the "shebang", as it is called: if the absolute first 2 bytes of an executable file are "#!" then the named executable following this is run and fed the following text as input.
Code:
#! /bin/bash
<... here comes some shell script...>
means: load "/bin/bash" and feed it the rest of the text as input. You can even force the system to use your own version if you want to try something with a special version you installed:
Code:
#! /my/private/version/of/bash
<... here comes some shell script...>
and you can specify any other executable as well, for instance awk:
Code:
#! /usr/bin/awk
<... some awk-script here ...>
I hope this helps.
bakunin
Thank you for the well though out explanation, I really appreciate you taking the time to write it. As someone who only dabbles in Linux very occasional it can get very daunting
---------- Post updated at 08:29 AM ---------- Previous update was at 08:28 AM ----------
Quote:
Originally Posted by Scrutinizer
dash may have less functionality than bash but it is a POSIX compliant and it is smaller and faster than bash, so systems startup scripts will run faster which leads to shorter boot times for example..
And now I know what POSIX means, thanks to Google. This has been a very informative thread, thank you!
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01-25-2015
