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I am currently taking a Controlled Assessment in a Computing GCSE and this is the task.

At the command prompt, type ls -a. Demonstrate and explain what happens. Modify this command so that it only shows hidden files beginning with the letter ‘b’.

I have already done ls -a and I tried ls -b, but it didn't work.

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  • ls -a | grep .b* should do I think – ddnomad Feb 23 '17 at 9:24
  • that's good. Please set my answer below as approved then :) – ddnomad Feb 23 '17 at 9:29
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    @ddnomad greping an ls output is unnecessarily complex, when you can specify the pattern with ls -a -d .b* - note that you need -d for not listing contents of the results. Also that grep will show files like 123.bWRONG. – Fiximan Feb 23 '17 at 9:35
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    All the information you need is in man ls. I suggest you read it. – terdon♦ Feb 23 '17 at 9:54
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The names of hidden files start with . (dot), there are none that start with b. To list names starting with .b use

$ ls .b*

This will also list the contents of any directory whose name starts with .b. Note that -a is not needed here as we explicitly give a filename pattern for the shell to match. Since the pattern starts with . (dot), it will match hidden files. The expanded pattern will be given to ls for processing.

To avoid listing the contents of directories, use

$ ls -d .b*

The above solutions will give an error if no name matches the pattern.

To only list the names of regular files whose names start with .b, use

$ for name in .b*; do test -f "$name" && printf '%s\n' "$name"; done

To get the output in a similar way as with plain ls (note that column is a non-standard utility):

$ for name in .b*; do test -f "$name" && printf '%s\n' "$name"; done | column

The last couple of solutions will not print anything of no name matches the pattern.

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  • When worrying about file type regular, a find command would be much simpler: find -maxdepth 1 -type f -name '.b*'. Also faster than a for loop. However, I assume ls-usage was intended. – Fiximan Feb 23 '17 at 10:02
  • @Fiximan If your find is able to do it that way, of course. Standard find needs a search path, and doesn't understand -maxdepth. This will also generate output with ./ prepended to the name (with GNU find). – Kusalananda♦ Feb 23 '17 at 10:06
  • I was aware of the implied . serach path being a GNU find variation, but not that even -maxdepth is, since BSD find had it (see man find )- good to know! – Fiximan Feb 23 '17 at 10:17
  • @Fiximan See pubs.opengroup.org/onlinepubs/9699919799/utilities/find.html – Kusalananda♦ Feb 23 '17 at 10:19
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ls is the command, and -a is the flag for the command. In order to see the files staring from b one can specify a pattern - .b* Where . means that the files are hidden and the * means everything else...

and in general when you don't know what a command does, read the manual - man ls

For avoiding listing of the contents of the listed items, use the -d option.

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